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+   "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd" >
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+  <head>
+    <title>
+      The Project Gutenberg eBook of The Radio Amateur's Hand Book, by A.
+      Frederick Collins
+    </title>
+  </head>
+  <body>
+    <h1>
+      The Project Gutenberg eBook of The Radio Amateur's Hand Book, by A.
+      Frederick Collins
+    </h1>
+<pre xml:space="preserve">
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+**Welcome To The World of Free Plain Vanilla Electronic Texts**
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+**eBooks Readable By Both Humans and By Computers, Since 1971**
+
+*****These eBooks Were Prepared By Thousands of Volunteers!*****
+
+
+Title: The Radio Amateur's Hand Book
+
+Author: A. Frederick Collins
+
+Release Date: November, 2004  [EBook #6935]
+[This file was first posted on February 13, 2003]
+
+Edition: 10a
+
+Language: English
+
+Character set encoding: iso-8859-1
+
+*** START OF THE PROJECT GUTENBERG EBOOK, THE RADIO AMATEUR'S HAND BOOK ***
+
+
+
+
+Produced by Alan Millar and the Online Distributed Proofreading Team.
+
+
+
+</pre>
+    <p>
+      <b>THE RADIO AMATEUR'S HAND BOOK</b>
+    </p>
+    <table cellspacing="20" summary="Illustration">
+      <tr>
+        <td align="center">
+          <i>Photograph unavailable</i>
+        </td>
+      </tr>
+      <tr>
+        <td align="center">
+          A. Frederick Collins, Inventor of the Wireless Telephone, 1899.
+          Awarded Gold Medal for same, Alaska Yukon Pacific Exposition, 1909.
+        </td>
+      </tr>
+    </table>
+    <hr />
+    <h1>
+      THE RADIO AMATEUR'S HAND BOOK
+    </h1>
+    <p>
+      <i>A Complete, Authentic and Informative Work on Wireless Telegraphy and
+      Telephony</i>
+    </p>
+    <p>
+      BY<br /> FREDERICK COLLINS
+    </p>
+    <p>
+      Inventor of the Wireless Telephone 1899; Historian of Wireless 1901-1910;
+      Author of "Wireless Telegraphy" 1905
+    </p>
+    <p>
+      1922
+    </p>
+    <hr />
+    <p>
+      TO<br /> WILLIAM MARCONI<br /> INVENTOR OF THE WIRELESS TELEGRAPH
+    </p>
+    <hr />
+    <h2>
+      <a name="intro" id="intro">INTRODUCTION</a>
+    </h2>
+    <p>
+      Before delving into the mysteries of receiving and sending messages
+      without wires, a word as to the history of the art and its present day
+      applications may be of service. While popular interest in the subject has
+      gone forward by leaps and bounds within the last two or three years, it
+      has been a matter of scientific experiment for more than a quarter of a
+      century.
+    </p>
+    <p>
+      The wireless telegraph was invented by William Marconi, at Bologna, Italy,
+      in 1896, and in his first experiments he sent dot and dash signals to a
+      distance of 200 or 300 feet. The wireless telephone was invented by the
+      author of this book at Narberth, Penn., in 1899, and in his first
+      experiments the human voice was transmitted to a distance of three blocks.
+    </p>
+    <p>
+      The first vital experiments that led up to the invention of the wireless
+      telegraph were made by Heinrich Hertz, of Germany, in 1888 when he showed
+      that the spark of an induction coil set up electric oscillations in an
+      open circuit, and that the energy of these waves was, in turn, sent out in
+      the form of electric waves. He also showed how they could be received at a
+      distance by means of a ring detector, which he called a <i>resonator</i>.
+    </p>
+    <p>
+      In 1890, Edward Branly, of France, showed that metal filings in a tube
+      cohered when electric waves acted on them, and this device he termed a <i>radio
+      conductor</i>; this was improved upon by Sir Oliver Lodge, who called it a
+      coherer. In 1895, Alexander Popoff, of Russia, constructed a receiving set
+      for the study of atmospheric electricity, and this arrangement was the
+      earliest on record of the use of a detector connected with an aerial and
+      the earth.
+    </p>
+    <p>
+      Marconi was the first to connect an aerial to one side of a spark gap and
+      a ground to the other side of it. He used an induction coil to energize
+      the spark gap, and a telegraph key in the primary circuit to break up the
+      current into signals. Adding a Morse register, which printed the dot and
+      dash messages on a tape, to the Popoff receptor he produced the first
+      system for sending and receiving wireless telegraph messages.
+    </p>
+    <table cellspacing="20" summary="Illustration">
+      <tr>
+        <td align="center">
+          <i>Photograph unavailable</i>
+        </td>
+      </tr>
+      <tr>
+        <td align="center">
+          Collins' Wireless Telephone Exhibited at the Madison Square Garden,
+          October 1908.
+        </td>
+      </tr>
+    </table>
+    <p>
+      After Marconi had shown the world how to telegraph without connecting
+      wires it would seem, on first thought, to be an easy matter to telephone
+      without wires, but not so, for the electric spark sets up damped and
+      periodic oscillations and these cannot be used for transmitting speech.
+      Instead, the oscillations must be of constant amplitude and continuous.
+      That a direct current arc light transforms a part of its energy into
+      electric oscillations was shown by Firth and Rogers, of England, in 1893.
+    </p>
+    <p>
+      The author was the first to connect an arc lamp with an aerial and a
+      ground, and to use a microphone transmitter to modulate the sustained
+      oscillations so set up. The receiving apparatus consisted of a variable
+      contact, known as a <i>pill-box</i> detector, which Sir Oliver Lodge had
+      devised, and to this was connected an Ericsson telephone receiver, then
+      the most sensitive made. A later improvement for setting up sustained
+      oscillations was the author's <i>rotating oscillation arc.</i>
+    </p>
+    <p>
+      Since those memorable days of more than two decades ago, wonderful
+      advances have been made in both of these methods of transmitting
+      intelligence, and the end is as yet nowhere in sight. Twelve or fifteen
+      years ago the boys began to get fun out of listening-in to what the ship
+      and shore stations were sending and, further, they began to do a little
+      sending on their own account. These youngsters, who caused the
+      professional operators many a pang, were the first wireless amateurs, and
+      among them experts were developed who are foremost in the practice of the
+      art today.
+    </p>
+    <p>
+      Away back there, the spark coil and the arc lamp were the only known means
+      for setting up oscillations at the sending end, while the electrolytic and
+      crystal detectors were the only available means for the amateur to receive
+      them. As it was next to impossible for a boy to get a current having a
+      high enough voltage for operating an oscillation arc lamp, wireless
+      telephony was out of the question for him, so he had to stick to the spark
+      coil transmitter which needed only a battery current to energize it, and
+      this, of course, limited him to sending Morse signals. As the electrolytic
+      detector was cumbersome and required a liquid, the crystal detector which
+      came into being shortly after was just as sensitive and soon displaced the
+      former, even as this had displaced the coherer.
+    </p>
+    <p>
+      A few years ahead of these amateurs, that is to say in 1905, J. A.
+      Fleming, of England, invented the vacuum tube detector, but ten more years
+      elapsed before it was perfected to a point where it could compete with the
+      crystal detector. Then its use became general and workers everywhere
+      sought to, and did improve it. Further, they found that the vacuum tube
+      would not only act as a detector, but that if energized by a direct
+      current of high voltage it would set up sustained oscillations like the
+      arc lamp, and the value of sustained oscillations for wireless telegraphy
+      as well as wireless telephony had already been discovered.
+    </p>
+    <p>
+      The fact that the vacuum tube oscillator requires no adjustment of its
+      elements, that its initial cost is much less than the oscillation arc,
+      besides other considerations, is the reason that it popularized wireless
+      telephony; and because continuous waves have many advantages over periodic
+      oscillations is the reason the vacuum tube oscillator is replacing the
+      spark coil as a wireless telegraph transmitter. Moreover, by using a
+      number of large tubes in parallel, powerful oscillations can be set up
+      and, hence, the waves sent out are radiated to enormous distances.
+    </p>
+    <p>
+      While oscillator tubes were being experimented with in the research
+      laboratories of the General Electric, the Westinghouse, the Radio
+      Corporation of America, and other big companies, all the youthful amateurs
+      in the country had learned that by using a vacuum tube as a detector they
+      could easily get messages 500 miles away. The use of these tubes as
+      amplifiers also made it possible to employ a loud speaker, so that a room,
+      a hall, or an out-of-door audience could hear clearly and distinctly
+      everything that was being sent out.
+    </p>
+    <p>
+      The boy amateur had only to let father or mother listen-in, and they were
+      duly impressed when he told them they were getting it from KDKA (the
+      Pittsburgh station of the Westinghouse Co.), for was not Pittsburgh 500
+      miles away! And so they, too, became enthusiastic wireless amateurs. This
+      new interest of the grown-ups was at once met not only by the
+      manufacturers of apparatus with complete receiving and sending sets, but
+      also by the big companies which began broadcasting regular programs
+      consisting of music and talks on all sorts of interesting subjects.
+    </p>
+    <p>
+      This is the wireless, or radio, as the average amateur knows it today. But
+      it is by no means the limit of its possibilities. On the contrary, we are
+      just beginning to realize what it may mean to the human race. The
+      Government is now utilizing it to send out weather, crop and market
+      reports. Foreign trade conditions are being reported. The Naval
+      Observatory at Arlington is wirelessing time signals.
+    </p>
+    <p>
+      Department stores are beginning to issue programs and advertise by radio!
+      Cities are also taking up such programs, and they will doubtless be
+      included soon among the regular privileges of the tax-payers. Politicians
+      address their constituents. Preachers reach the stay-at-homes. Great
+      singers thrill thousands instead of hundreds. Soon it will be possible to
+      hear the finest musical programs, entertainers, and orators, without
+      budging from one's easy chair.
+    </p>
+    <p>
+      In the World War wireless proved of inestimable value. Airplanes, instead
+      of flying aimlessly, kept in constant touch with headquarters. Bodies of
+      troops moved alertly and intelligently. Ships at sea talked freely, over
+      hundreds of miles. Scouts reported. Everywhere its invisible aid was
+      invoked.
+    </p>
+    <p>
+      In time of peace, however, it has proved and will prove the greatest
+      servant of mankind. Wireless messages now go daily from continent to
+      continent, and soon will go around the world with the same facility. Ships
+      in distress at sea can summon aid. Vessels everywhere get the day's news,
+      even to baseball scores. Daily new tasks are being assigned this tireless,
+      wireless messenger.
+    </p>
+    <p>
+      Messages have been sent and received by moving trains, the Lackawanna and
+      the Rock Island railroads being pioneers in this field. Messages have also
+      been received by automobiles, and one inventor has successfully
+      demonstrated a motor car controlled entirely by wireless. This method of
+      communication is being employed more and more by newspapers. It is also of
+      great service in reporting forest fires.
+    </p>
+    <p>
+      Colleges are beginning to take up the subject, some of the first being
+      Tufts College, Hunter College, Princeton, Yale, Harvard, and Columbia,
+      which have regularly organized departments for students in wireless.
+    </p>
+    <p>
+      Instead of the unwieldy and formidable looking apparatus of a short time
+      ago, experimenters are now vying with each other in making small or novel
+      equipment. Portable sets of all sorts are being fashioned, from one which
+      will go into an ordinary suitcase, to one so small it will easily slip
+      into a Brownie camera. One receiver depicted in a newspaper was one inch
+      square! Another was a ring for the finger, with a setting one inch by
+      five-eighths of an inch, and an umbrella as a "ground." Walking sets with
+      receivers fastened to one's belt are also common. Daily new novelties and
+      marvels are announced.
+    </p>
+    <p>
+      Meanwhile, the radio amateur to whom this book is addressed may have his
+      share in the joys of wireless. To get all of these good things out of the
+      ether one does not need a rod or a gun--only a copper wire made fast at
+      either end and a receiving set of some kind. If you are a sheer beginner,
+      then you must be very careful in buying your apparatus, for since the
+      great wave of popularity has washed wireless into the hearts of the
+      people, numerous companies have sprung up and some of these are selling
+      the veriest kinds of junk.
+    </p>
+    <p>
+      And how, you may ask, are you going to be able to know the good from the
+      indifferent and bad sets? By buying a make of a firm with an established
+      reputation. I have given a few offhand at the end of this book. Obviously
+      there are many others of merit--so many, indeed, that it would be quite
+      impossible to get them all in such a list, but these will serve as a guide
+      until you can choose intelligently for yourself.
+    </p>
+    <p>
+      F. C.
+    </p>
+    <hr />
+    <h2>
+      <a name="contents" id="contents">CONTENTS</a>
+    </h2>
+    <p>
+      <b>CHAPTER</b>
+    </p>
+    <h3>
+      <a href="#chap01">I. HOW TO BEGIN WIRELESS</a>
+    </h3>
+    <p>
+      Kinds of Wireless Systems--Parts of a Wireless System--The Easiest Way to
+      Start--About Aerial Wire Systems--About the Receiving Apparatus--About
+      Transmitting Stations--Kinds of Transmitters--The Spark Gap Wireless
+      Telegraph Transmitter--The Vacuum Table Telegraph Transmitter--The
+      Wireless Telephone Transmitter.
+    </p>
+    <h3>
+      <a href="#chap02">II. PUTTING UP YOUR AERIAL</a>
+    </h3>
+    <p>
+      Kinds of Aerial Wire Systems--How to Put Up a Cheap Receiving Aerial--A
+      Two-wire Aerial--Connecting in the Ground--How to Put up a Good Aerial--An
+      Inexpensive Good Aerial--The Best Aerial That Can be Made--Assembling the
+      Aerial--Making a Good Ground.
+    </p>
+    <h3>
+      <a href="#chap03">III. SIMPLE TELEGRAPH AND TELEPHONE RECEIVING SETS</a>
+    </h3>
+    <p>
+      Assembled Wireless Receiving Sets--Assembling Your Own Receiving Set--The
+      Crystal Detector--The Tuning Coil--The Loose Coupled Tuning Coil--Fixed
+      and Variable Condensers--About Telephone Receivers-- Connecting Up the
+      Parts--Receiving Set No. 2--Adjusting the No. 1 Set--The Tuning
+      Coil--Adjusting the No. 2 Set.
+    </p>
+    <h3>
+      <a href="#chap04">IV. SIMPLE TELEGRAPH SENDING SETS</a>
+    </h3>
+    <p>
+      A Cheap Transmitting Set (No. 1)--The Spark Coil--The Battery--The
+      Telegraph Key--The Spark Gap--The Tuning Coil--The High-tension
+      Condenser--A Better Transmitting Set (No. 2)--The Alternating Current
+      Transformer--The Wireless Key--The Spark Gap--The High-tension
+      Condenser--The Oscillation Transformer--Connecting Up the Apparatus--For
+      Direct Current--How to Adjust Your Transmitter. Turning With a Hot Wire
+      Ammeter--To Send Out a 200-meter Wave Length--The Use of the Aerial
+      Switch--Aerial Switch for a Complete Sending and Receiving Set--Connecting
+      in the Lightning Switch.
+    </p>
+    <h3>
+      <a href="#chap05">V. ELECTRICITY SIMPLY EXPLAINED</a>
+    </h3>
+    <p>
+      Electricity at Rest and in Motion--The Electric Current and its
+      Circuit--Current and the Ampere--Resistance and the Ohm--What Ohm's Law
+      Is--What the Watt and Kilowatt Are--Electromagnetic Induction--Mutual
+      Induction--High-frequency Currents--Constants of an Oscillation
+      Circuit--What Capacitance Is--What Inductance Is--What Resistance Is--The
+      Effect of Capacitance.
+    </p>
+    <h3>
+      <a href="#chap06">VI. HOW THE TRANSMITTING AND RECEIVING SETS WORK</a>
+    </h3>
+    <p>
+      How Transmitting Set No. 1 Works--The Battery and Spark Coil
+      Circuit--Changing the Primary Spark Coil Current Into Secondary
+      Currents--What Ratio of Transformation Means--The Secondary Spark Coil
+      Circuit--The Closed Oscillation Circuit--How Transmitting Set No. 2
+      Works-With Alternating Current--With Direct Current--The Rotary Spark
+      Gap--The Quenched Spark Gap--The Oscillation Transformer--How Receiving
+      Set No. 1 Works--How Receiving Set No. 2 Works.
+    </p>
+    <h3>
+      <a href="#chap07">VII. MECHANICAL AND ELECTRICAL TUNING</a>
+    </h3>
+    <p>
+      Damped and Sustained Mechanical Vibrations--Damped and Sustained
+      Oscillations--About Mechanical Tuning--About Electric Tuning.
+    </p>
+    <h3>
+      <a href="#chap08">VIII. A SIMPLE VACUUM TUBE DETECTOR RECEIVING SET</a>
+    </h3>
+    <p>
+      Assembled Vacuum Tube Receiving Set--A Simple Vacuum Tube Receiving
+      Set--The Vacuum Tube Detector--Three Electrode Vacuum Tube Detector--The
+      Dry Cell and Storage Batteries--The Filament Rheostat--Assembling the
+      Parts--Connecting Up the Parts--Adjusting the Vacuum Tube Detector
+      Receiving Set.
+    </p>
+    <h3>
+      <a href="#chap09">IX. VACUUM TUBE AMPLIFIER RECEIVING SETS</a>
+    </h3>
+    <p>
+      A Grid Leak Amplifier Receiving Set. With Crystal Detector--The Fixed
+      Resistance Unit, or Grid Leak--Assembling the Parts for a Crystal Detector
+      Set--Connecting up the Parts for a Crystal Detector--A Grid Leak
+      Amplifying Receiving Set With Vacuum Tube Detector--A Radio Frequency
+      Transformer Amplifying Receiving Set--An Audio Frequency Transformer
+      Amplifying Receiving Set--A Six Step Amplifier Receiving Set with a Loop
+      Aerial--How to Prevent Howling.
+    </p>
+    <h3>
+      <a href="#chap10">X. REGENERATIVE AMPLIFICATION RECEIVING SETS</a>
+    </h3>
+    <p>
+      The Simplest Type of Regenerative Receiving Set--With Loose Coupled Tuning
+      Coil--Connecting Up the Parts--An Efficient Regenerative Receiving Set.
+      With Three Coil Loose Coupler--The A Battery Potentiometer--The Parts and
+      How to Connect Them Up--A Regenerative Audio Frequency Amplifier--The
+      Parts and How to Connect Them Up.
+    </p>
+    <h3>
+      <a href="#chap11">XI. SHORT WAVE REGENERATIVE RECEIVING SETS</a>
+    </h3>
+    <p>
+      A Short Wave Regenerative Receiver, with One Variometer and Three Variable
+      Condensers--The Variocoupler--The Variometer--Connecting Up the
+      Parts--Short Wave Regenerative Receiver with Two Variometers and Two
+      Variable Condensers--The Parts and How to Connect Them Up.
+    </p>
+    <h3>
+      <a href="#chap12">XII. INTERMEDIATE AND LONG WAVE REGENERATIVE RECEIVING
+      SETS</a>
+    </h3>
+    <p>
+      Intermediate Wave Receiving Sets--Intermediate Wave Set With Loading
+      Coils--The Parts and How to Connect Them Up--An Intermediate Wave Set with
+      Variocoupler Inductance Coils--The Parts and How to Connect Them Up--A
+      Long Wave Receiving Set--The Parts and How to Connect Them Up.
+    </p>
+    <h3>
+      <a href="#chap13">XIII. HETERODYNE OR BEAT LONG WAVE TELEGRAPH RECEIVING
+      SET</a>
+    </h3>
+    <p>
+      What the Heterodyne or Beat Method Is--The Autodyne or Self-heterodyne
+      Long Wave Receiving Set--The Parts and Connections of an Autodyne or
+      Self-heterodyne, Receiving Set--The Separate Heterodyne Long Wave
+      Receiving Set--The Parts and Connections of a Separate Heterodyne Long
+      Wave Receiving Set.
+    </p>
+    <h3>
+      <a href="#chap14">XIV. HEADPHONES AND LOUD SPEAKERS</a>
+    </h3>
+    <p>
+      Wireless Headphones--How a Bell Telephone Receiver is Made--How a Wireless
+      Headphone is Made--About Resistance, Turns of Wire and Sensitivity of
+      Headphones--The Impedance of Headphones--How the Headphones Work--About
+      Loud Speakers--The Simplest Type of Loud Speaker--Another Simple Kind of
+      Loud Speaker--A Third Kind of Simple Loud Speaker--A Super Loud Speaker.
+    </p>
+    <h3>
+      <a href="#chap15">XV. OPERATION OF VACUUM TUBE RECEPTORS</a>
+    </h3>
+    <p>
+      What is Meant by Ionization--How Electrons are Separated from
+      Atoms--Action of the Two Electrode Vacuum Tube--How the Two Electrode Tube
+      Acts as a Detector--How the Three Electrode Tube Acts as a Detector--How
+      the Vacuum Tube Acts as an Amplifier--The Operation of a Simple Vacuum
+      Tube Receiving Set--Operation of a Regenerative Vacuum Tube Receiving
+      Set--Operation of Autodyne and Heterodyne Receiving Sets--The Autodyne, or
+      Self-Heterodyne Receiving Set--The Separate Heterodyne Receiving Set.
+    </p>
+    <h3>
+      <a href="#chap16">XVI. CONTINUOUS WAVE TELEGRAPH TRANSMITTING SETS WITH
+      DIRECT CURRENT</a>
+    </h3>
+    <p>
+      Sources of Current for Telegraph Transmitting Sets--An Experimental
+      Continuous Wave Telegraph Transmitter--The Apparatus You Need--The Tuning
+      Coil--The Condensers--The Aerial Ammeter--The Buzzer and Dry Cell--The
+      Telegraph Key--The Vacuum Tube Oscillator--The Storage Battery--The
+      Battery Rheostat--The Oscillation Choke Coil--Transmitter Connectors--The
+      Panel Cutout--Connecting Up the Transmitting Apparatus--A 100-mile C. W.
+      Telegraph Transmitter--The Apparatus You Need--The Tuning Coil--The Aerial
+      Condenser--The Aerial Ammeter--The Grid and Blocking Condensers--The Key
+      Circuit Apparatus--The 5 Watt Oscillator Vacuum Tube--The Storage Battery
+      and Rheostat--The Filament Voltmeter--The Oscillation Choke Coil--The
+      Motor-generator Set--The Panel Cut-out--The Protective
+      Condenser--Connecting Up the Transmitting Apparatus--A 200-mile C. W.
+      Telegraph Transmitter--A 500-mile C. W. Telegraph Transmitter--The
+      Apparatus and Connections-- The 50-watt Vacuum Tube Oscillator--The Aerial
+      Ammeter--The Grid Leak Resistance--The Oscillation Choke Coil--The
+      Filament Rheostat--The Filament Storage Battery--The Protective
+      Condenser--The Motor-generator--A 1000-mile C. W. Telegraph Transmitter.
+    </p>
+    <h3>
+      <a href="#chap17">XVII. CONTINUOUS WAVE TELEGRAPH TRANSMITTING SETS WITH
+      ALTERNATING CURRENT</a>
+    </h3>
+    <p>
+      A 100-mile C. W. Telegraph Transmitting Set--The Apparatus Required--The
+      Choke Coils--The Milli-ammeter--The A. C. Power Transformer--Connecting Up
+      the Apparatus--A 200- to 500-mile C. W. Telegraph Transmitting Set-A 500-
+      to 1000-mile C. W. Telegraph Transmitting Set--The Apparatus Required--The
+      Alternating Current Power Transformer-Connecting Up the Apparatus.
+    </p>
+    <h3>
+      <a href="#chap18">XVIII. WIRELESS TELEPHONE TRANSMITTING SETS WITH DIRECT
+      AND ALTERNATING CURRENTS</a>
+    </h3>
+    <p>
+      A Short Distance Wireless Telephone Transmitting Set--With 110-volt Direct
+      Lighting Current--The Apparatus You Need--The Microphone
+      Transmitter--Connecting Up the Apparatus--A 25- to 50-mile Wireless
+      Telephone Transmitter--With Direct Current Motor Generator--The Apparatus
+      You Need--The Telephone Induction Coil--The Microphone Transformer--The
+      Magnetic Modulator--How the Apparatus is Connected Up--A 50- to 100-mile
+      Wireless Telephone Transmitter--With Direct Current Motor Generator--The
+      Oscillation Choke Coil--The Plate and Grid Circuit Reactance
+      Coils--Connecting up the Apparatus--A 100- to 200-mile Wireless Telephone
+      Transmitter--With Direct Current Motor Generator--A 50- to 100-mile
+      Wireless Telephone Transmitting Set--With 100-volt Alternating
+      Current--The Apparatus You Need--The Vacuum Tube Rectifier--The Filter
+      Condensers--The Filter Reactance Coil-- Connecting Up the Apparatus--A
+      100- to 200-mile Wireless Telephone Transmitting Set--With 110-volt
+      Alternating Current--Apparatus Required.
+    </p>
+    <h3>
+      <a href="#chap19">XIX. THE OPERATION OF VACUUM TUBE TRANSMITTERS</a>
+    </h3>
+    <p>
+      The Operation of the Vacuum Tube Oscillator--The Operation of C. W.
+      Telegraph Transmitters with Direct Current--Short Distance C. W.
+      Transmitter--The Operation of the Key Circuit--The Operation of C. W.
+      Telegraph Transmitting with Direct Current--The Operation of C. W.
+      Telegraph Transmitters with Alternating Current--With a Single Oscillator
+      Tube--Heating the Filament with Alternating Current--The Operation of C.
+      W. Telegraph Transmitters with Alternating Current-- With Two Oscillator
+      Tubes--The Operation of Wireless Telephone Transmitters with Direct
+      Current--Short Distance Transmitter--The Microphone Transmitter--The
+      Operation of Wireless Telephone Transmitters with Direct Current--Long
+      Distance Transmitters--The Operation of Microphone Modulators--The
+      Induction Coil--The Microphone Transformer--The Magnetic
+      Modulator--Operation of the Vacuum Tube as a Modulator--The Operation of
+      Wireless Telephone Transmitters with Alternating Current--The Operation of
+      Rectifier Vacuum Tubes--The Operation of Reactors and Condensers.
+    </p>
+    <h3>
+      <a href="#chap20">XX. HOW TO MAKE A RECEIVING SET FOR $5.00 OR LESS.</a>
+    </h3>
+    <p>
+      The Crystal Detector--The Tuning Coil--The Headphone--How to Mount the
+      Parts--The Condenser--How to Connect Up the Receptor.
+    </p>
+    <h3>
+      <a href="#appendix">APPENDIX</a>
+    </h3>
+    <p>
+      Useful Information--<a href="#glossary">Glossary</a>--<a href="#donts">Wireless
+      Don'ts</a>.
+    </p>
+    <h2>
+      LIST OF FIGURES
+    </h2>
+    <ul>
+      <li>
+        <a href="#fig001">Fig. 1.</a>--Simple Receiving Set
+      </li>
+      <li>
+        <a href="#fig001">Fig. 2.</a>--Simple Transmitting Set
+      </li>
+      <li>
+        <a href="#fig003">(A) Fig. 3.</a>--Flat Top, or Horizontal Aerial
+      </li>
+      <li>
+        <a href="#fig003">(B) Fig. 3.</a>--Inclined Aerial
+      </li>
+      <li>
+        <a href="#fig004">(A) Fig. 4.</a>--Inverted L Aerial
+      </li>
+      <li>
+        <a href="#fig004">(B) Fig. 4.</a>--T Aerial
+      </li>
+      <li>
+        <a href="#fig005">Fig. 5.</a>--Material for a Simple Aerial Wire System
+      </li>
+      <li>
+        <a href="#fig006a">(A) Fig. 6.</a>--Single Wire Aerial for Receiving
+      </li>
+      <li>
+        <a href="#fig006b">(B) Fig. 6.</a>--Receiving Aerial with Spark Gap
+        Lightning Arrester
+      </li>
+      <li>
+        <a href="#fig006c">(C) Fig. 6.</a>--Aerial with Lightning Switch
+      </li>
+      <li>
+        <a href="#fig007">Fig. 7.</a>--Two-wire Aerial
+      </li>
+      <li>
+        <a href="#fig008a">(A) Fig. 8.</a>--Part of a Good Aerial
+      </li>
+      <li>
+        <a href="#fig008b">(B) Fig. 8.</a>--The Spreaders
+      </li>
+      <li>
+        <a href="#fig009ab">(A) Fig. 9.</a>--The Middle Spreader
+      </li>
+      <li>
+        <a href="#fig009ab">(B) Fig. 9.</a>--One End of Aerial Complete
+      </li>
+      <li>
+        <a href="#fig009c">(C) Fig. 9.</a>--The Leading in Spreader
+      </li>
+      <li>
+        <a href="#fig010ab">(A) Fig. 10.</a>--Cross Section of Crystal Detector
+      </li>
+      <li>
+        <a href="#fig010ab">(B) Fig. 10.</a>--The Crystal Detector Complete
+      </li>
+      <li>
+        <a href="#fig011ab">(A) Fig. 11.</a>--Schematic Diagram of a Double
+        Slide Tuning Coil
+      </li>
+      <li>
+        <a href="#fig011ab">(B) Fig. 11.</a>--Double Slide Tuning Coil Complete
+      </li>
+      <li>
+        <a href="#fig012ab">(A) Fig. 12.</a>--Schematic Diagram of a Loose
+        Coupler
+      </li>
+      <li>
+        <a href="#fig012ab">(B) Fig. 12.</a>--Loose Coupler Complete
+      </li>
+      <li>
+        <a href="#fig013ab">(A) Fig. 13.</a>--How a Fixed Receiving Condenser is
+        Built up
+      </li>
+      <li>
+        <a href="#fig013ab">(B) Fig. 13.</a>--The Fixed Condenser Complete
+      </li>
+      <li>
+        <a href="#fig013cd">(C) and (D) Fig. 13.</a>--Variable Rotary Condenser
+      </li>
+      <li>
+        <a href="#fig014">Fig. 14.</a>--Pair of Wireless Headphones
+      </li>
+      <li>
+        <a href="#fig015a">(A) Fig. 15.</a>--Top View of Apparatus Layout for
+        Receiving Set No. 1
+      </li>
+      <li>
+        <a href="#fig015b">(B) Fig. 15.</a>--Wiring Diagram for Receiving Set
+        No. 1
+      </li>
+      <li>
+        <a href="#fig016a">(A) Fig. 16.</a>--Top View of Apparatus Layout for
+        Receiving Set No. 2
+      </li>
+      <li>
+        <a href="#fig016b">(B) Fig. 16.</a>--Wiring Diagram for Receiving Set
+        No. 2
+      </li>
+      <li>
+        <a href="#fig017">Fig. 17.</a>--Adjusting the Receiving Set
+      </li>
+      <li>
+        <a href="#fig018ab">(A) and (B) Fig. 18.</a>--Types of Spark Coils for
+        Set No. 1
+      </li>
+      <li>
+        <a href="#fig018c">(C) Fig. 18.</a>--Wiring Diagram of Spark Coil
+      </li>
+      <li>
+        <a href="#fig019">Fig. 19.</a>--Other Parts for Transmitting Set No. 1
+      </li>
+      <li>
+        <a href="#fig020a">(A) Fig. 20.</a>--Top View of Apparatus Layout for
+        Sending Set No. 1
+      </li>
+      <li>
+        <a href="#fig020b">(B) Fig. 20.</a>--Wiring of Diagram for Sending Set
+        No. 1
+      </li>
+      <li>
+        <a href="#fig021">Fig. 21.</a>--Parts for Transmitting Set No. 2
+      </li>
+      <li>
+        <a href="#fig022a">(A) Fig. 22.</a>--Top View of Apparatus Layout for
+        Sending Set No. 2
+      </li>
+      <li>
+        <a href="#fig022b">(B) Fig. 22.</a>--Wiring Diagram for Sending Set No.
+        2
+      </li>
+      <li>
+        <a href="#fig023">Fig. 23.</a>--Using a 110-volt Direct Current with an
+        Alternating current Transformer
+      </li>
+      <li>
+        <a href="#fig024">Fig. 24.</a>--Principle of the Hot Wire Ammeter
+      </li>
+      <li>
+        <a href="#fig025">Fig. 25.</a>--Kinds of Aerial Switches
+      </li>
+      <li>
+        <a href="#fig026">Fig. 26.</a>--Wiring Diagram for a Complete Sending
+        and Receiving Set No. 1
+      </li>
+      <li>
+        <a href="#fig027">Fig. 27.</a>--Wiring Diagram for Complete Sending and
+        Receiving Set No. 2
+      </li>
+      <li>
+        <a href="#fig028">Fig. 28.</a>--Water Analogue for Electric Pressure
+      </li>
+      <li>
+        <a href="#fig029">Fig. 29.</a>--Water Analogues for Direct and
+        Alternating Currents
+      </li>
+      <li>
+        <a href="#fig030">Fig. 30.</a>--How the Ammeter and Voltmeter are Used
+      </li>
+      <li>
+        <a href="#fig031">Fig. 31.</a>--Water Valve Analogue of Electric
+        Resistance
+      </li>
+      <li>
+        <a href="#fig032ab">(A) and (B) Fig. 32.</a>--How an Electric Current is
+        Changed into Magnetic Lines of Force and These into an Electric Current
+      </li>
+      <li>
+        <a href="#fig032cd">(C) and (D) Fig. 32.</a>--How an Electric Current
+        Sets up a Magnetic Field
+      </li>
+      <li>
+        <a href="#fig033">Fig. 33.</a>--The Effect of Resistance on the
+        Discharge of an Electric Current
+      </li>
+      <li>
+        <a href="#fig034">Fig. 34.</a>--Damped and Sustained Mechanical
+        Vibrations
+      </li>
+      <li>
+        <a href="#fig035">Fig. 35.</a>--Damped and Sustained Electric
+        Oscillations
+      </li>
+      <li>
+        <a href="#fig036">Fig. 36.</a>--Sound Wave and Electric Wave Tuned
+        Senders and Receptors
+      </li>
+      <li>
+        <a href="#fig037">Fig. 37.</a>--Two Electrode Vacuum Tube Detectors
+      </li>
+      <li>
+        <a href="#fig038">Fig. 38.</a>--Three Electrode Vacuum Tube Detector and
+        Battery Connections
+      </li>
+      <li>
+        <a href="#fig039">Fig. 39.</a>--A and B Batteries for Vacuum Tube
+        Detectors
+      </li>
+      <li>
+        <a href="#fig040">Fig. 40.</a>--Rheostat for the A or Storage-battery
+        Current
+      </li>
+      <li>
+        <a href="#fig041a">(A) Fig. 41.</a>--Top View of Apparatus Layout for
+        Vacuum Tube Detector Receiving Set
+      </li>
+      <li>
+        <a href="#fig041b">(B) Fig. 41.</a>--Wiring Diagram of a Simple Vacuum
+        Tube Receiving Set
+      </li>
+      <li>
+        <a href="#fig042">Fig. 42.</a>--Grid Leaks and How to Connect them Up
+      </li>
+      <li>
+        <a href="#fig043">Fig. 43.</a>--Crystal Detector Receiving Set with
+        Vacuum Tube Amplifier (Resistance Coupled)
+      </li>
+      <li>
+        <a href="#fig044a">(A) Fig. 44.</a>--Vacuum Tube Detector Receiving Set
+        with One Step Amplifier (Resistance Coupled)
+      </li>
+      <li>
+        <a href="#fig044b">(B) Fig. 44.</a>--Wiring Diagram for Using One A or
+        Storage Battery with an Amplifier and a Detector Tube
+      </li>
+      <li>
+        <a href="#fig045a">(A) Fig. 45.</a>--Wiring Diagram for Radio Frequency
+        Transformer Amplifying Receiving Set
+      </li>
+      <li>
+        <a href="#fig045b">(B) Fig. 45.</a>--Radio Frequency Transformer
+      </li>
+      <li>
+        <a href="#fig046a">(A) Fig. 46.</a>--Audio Frequency Transformer
+      </li>
+      <li>
+        <a href="#fig046b">(B) Fig. 46.</a>--Wiring Diagram for Audio Frequency
+        Transformer Amplifying Receiving Set. (With Vacuum Tube Detector and Two
+        Step Amplifier Tubes)
+      </li>
+      <li>
+        <a href="#fig047a">(A) Fig. 47.</a>--Six Step Amplifier with Loop Aerial
+      </li>
+      <li>
+        <a href="#fig047b">(B) Fig. 47.</a>--Efficient Regenerative Receiving
+        Set (With Three Coil Loose Coupler Tuner)
+      </li>
+      <li>
+        <a href="#fig048">Fig. 48.</a>--Simple Regenerative Receiving Set (With
+        Loose Coupler Tuner)
+      </li>
+      <li>
+        <a href="#fig049a">(A) Fig. 49.</a>--Diagram of Three Coil Loose Coupler
+      </li>
+      <li>
+        <a href="#fig049b">(B) Fig. 49.</a>--Three Coil Loose Coupler Tuner
+      </li>
+      <li>
+        <a href="#fig050">Fig. 50.</a>--Honeycomb Inductance Coil
+      </li>
+      <li>
+        <a href="#fig051a">Fig. 51.</a>--The Use of the Potentiometer
+      </li>
+      <li>
+        <a href="#fig052">Fig. 52.</a>--Regenerative Audio Frequency Amplifier
+        Receiving Set
+      </li>
+      <li>
+        <a href="#fig053">Fig. 53.</a>--How the Vario Coupler is Made and Works
+      </li>
+      <li>
+        <a href="#fig054">Fig. 54.</a>--How the Variometer is Made and Works
+      </li>
+      <li>
+        <a href="#fig055">Fig. 55.</a>--Short Wave Regenerative Receiving Set
+        (One Variometer and Three Variable Condensers)
+      </li>
+      <li>
+        <a href="#fig056">Fig. 56.</a>--Short Wave Regenerative Receiving Set
+        (Two Variometer and Two Variable Condensers)
+      </li>
+      <li>
+        <a href="#fig057">Fig. 57.</a>--Wiring Diagram Showing Fixed Loading
+        Coils for Intermediate Wave Set
+      </li>
+      <li>
+        <a href="#fig058">Fig. 58.</a>--Wiring Digram of Intermediate Wave
+        Receptor with One Vario Coupler and 12 Section Bank-wound Inductance
+        Coil
+      </li>
+      <li>
+        <a href="#fig059">Fig. 59.</a>--Wiring Diagram Showing Long Wave
+        Receptor with Vario Couplers and 8 Bank-wound Inductance Coils
+      </li>
+      <li>
+        <a href="#fig060">Fig. 60.</a>--Wiring Diagram of Long Wave Autodyne, or
+        Self-heterodyne Receptor (Compare with Fig. 77)
+      </li>
+      <li>
+        <a href="#fig061">Fig. 61.</a>--Wiring Diagram of Long Wave Separate
+        Heterodyne Receiving Set
+      </li>
+      <li>
+        <a href="#fig062">Fig. 62.</a>--Cross Section of Bell Telephone Receiver
+      </li>
+      <li>
+        <a href="#fig063">Fig. 63.</a>--Cross Section of Wireless Headphone
+      </li>
+      <li>
+        <a href="#fig064">Fig. 64.</a>--The Wireless Headphone
+      </li>
+      <li>
+        <a href="#fig065">Fig. 65.</a>--Arkay Loud Speaker
+      </li>
+      <li>
+        <a href="#fig066">Fig. 66.</a>--Amplitone Loud Speaker
+      </li>
+      <li>
+        <a href="#fig067">Fig. 67.</a>--Amplitron Loud Speaker
+      </li>
+      <li>
+        <a href="#fig068">Fig. 68.</a>--Magnavox Loud Speaker
+      </li>
+      <li>
+        <a href="#fig069">Fig. 69.</a>--Schematic Diagram of an Atom
+      </li>
+      <li>
+        <a href="#fig070">Fig. 70.</a>--Action of Two-electrode Vacuum Tube
+      </li>
+      <li>
+        <a href="#fig071ab">(A) and (B) Fig. 71.</a>--How a Two-electrode Tube
+        Acts as Relay or a Detector
+      </li>
+      <li>
+        <a href="#fig071c">(C) Fig. 71.</a>--Only the Positive Part of
+        Oscillations Goes through the Tube
+      </li>
+      <li>
+        <a href="#fig072ab">(A) and (B) Fig. 72.</a>--How the Positive and
+        Negative Voltages of the Oscillations Act on the Electrons
+      </li>
+      <li>
+        <a href="#fig072c">(C) Fig. 72.</a>--How the Three-electrode Tube Acts
+        as Detector and Amplifier
+      </li>
+      <li>
+        <a href="#fig072d">(D) Fig. 72.</a>--How the Oscillations Control the
+        Flow of the Battery Current through the Tube
+      </li>
+      <li>
+        <a href="#fig073">Fig. 73.</a>--How the Heterodyne Receptor Works
+      </li>
+      <li>
+        <a href="#fig074">Fig. 74.</a>--Separate Heterodyne Oscillator
+      </li>
+      <li>
+        <a href="#fig075a">(A) Fig. 75.</a>--Apparatus for Experimental C. W.
+        Telegraph Transmitter.
+      </li>
+      <li>
+        <a href="#fig075b">(B) Fig. 75.</a>--Apparatus for Experimental C. W.
+        Telegraph Transmitter.
+      </li>
+      <li>
+        <a href="#fig076">Fig. 76.</a>--Experimental C. W. Telegraph Transmitter
+      </li>
+      <li>
+        <a href="#fig077">Fig. 77.</a>--Apparatus of 100-mile C. W. Telegraph
+        Transmitter
+      </li>
+      <li>
+        <a href="#fig078">Fig. 78.</a>--5- to 50-watt C. W. Telegraph
+        Transmitter (with a Single Oscillation Tube)
+      </li>
+      <li>
+        <a href="#fig079">Fig. 79.</a>--200-mile C. W. Telegraph Transmitter
+        (with Two Tubes in Parallel)
+      </li>
+      <li>
+        <a href="#fig080">Fig. 80.</a>--50-watt Oscillator Vacuum Tube
+      </li>
+      <li>
+        <a href="#fig081">Fig. 81.</a>--Alternating Current Power Transformer
+        (for C. W. Telegraphy and Wireless Telephony)
+      </li>
+      <li>
+        <a href="#fig082">Fig. 82.</a>--Wiring Diagram for 200- to 500-mile C.
+        W. Telegraph Transmitting Set. (With Alternating Current.)
+      </li>
+      <li>
+        <a href="#fig083">Fig. 83.</a>--Wiring Diagram for 500- to 1000-mile C.
+        W. Telegraph Transmitter
+      </li>
+      <li>
+        <a href="#fig084">Fig. 84.</a>--Standard Microphone Transmitter
+      </li>
+      <li>
+        <a href="#fig085">Fig. 85.</a>--Wiring Diagram of Short Distance
+        Wireless Telephone Set. (Microphone in Aerial Wire.)
+      </li>
+      <li>
+        <a href="#fig086">Fig. 86.</a>--Telephone Induction Coil (used with
+        Microphone Transmitter).
+      </li>
+      <li>
+        <a href="#fig087">Fig. 87.</a>--Microphone Transformer Used with
+        Microphone Transmitter
+      </li>
+      <li>
+        <a href="#fig088">Fig. 88.</a>--Magnetic Modulator Used with Microphone
+        Transmitter
+      </li>
+      <li>
+        <a href="#fig089a">(A) Fig. 89.</a>--Wiring Diagram of 25--to 50-mile
+        Wireless Telephone. (Microphone Modulator Shunted Around Grid-leak
+        Condenser)
+      </li>
+      <li>
+        <a href="#fig089b">(B) Fig. 89.</a>--Microphone Modulator Connected in
+        Aerial Wire
+      </li>
+      <li>
+        <a href="#fig090">Fig. 90.</a>--Wiring Diagram of 50- to 100-mile
+        Wireless Telephone Transmitting Set
+      </li>
+      <li>
+        <a href="#fig091">Fig. 91.</a>--Plate and Grid Circuit Reactor
+      </li>
+      <li>
+        <a href="#fig092">Fig. 92.</a>--Filter Reactor for Smoothing Out
+        Rectified Currents
+      </li>
+      <li>
+        <a href="#fig093">Fig. 93.</a>--100- to 200-mile Wireless Telephone
+        Transmitter
+      </li>
+      <li>
+        <a href="#fig094ab">(A) and (B) Fig. 94.</a>--Operation of Vacuum Tube
+        Oscillators
+      </li>
+      <li>
+        <a href="#fig094c">(C) Fig. 94.</a>--How a Direct Current Sets up
+        Oscillations
+      </li>
+      <li>
+        <a href="#fig095">Fig. 95.</a>--Positive Voltage Only Sets up
+        Oscillations
+      </li>
+      <li>
+        <a href="#fig096">Fig. 96.</a>--Rasco Baby Crystal Detector
+      </li>
+      <li>
+        <a href="#fig097">Fig. 97.</a>--How the Tuning Coil is Made
+      </li>
+      <li>
+        <a href="#fig098">Fig. 98.</a>--Mesco loop-ohm Head Set
+      </li>
+      <li>
+        <a href="#fig099">Fig. 99.</a>--Schematic Layout of the $5.00 Receiving
+        Set
+      </li>
+      <li>
+        <a href="#fig100">Fig. 100.</a>--Wiring Diagram for the $5.00 Receiving
+        Set
+      </li>
+    </ul>
+    <h2>
+      LIST OF ILLUSTRATIONS
+    </h2>
+    <ul>
+      <li>
+        Frederick Collins, Inventor of the Wireless Telephone, 1899. Awarded
+        Gold Medal for same, Alaska Yukon Pacific Exposition, 1909
+      </li>
+      <li>
+        Collins' Wireless Telephone Exhibited at the Madison Square Garden,
+        October, 1908
+      </li>
+      <li>
+        General Pershing "Listening-in"
+      </li>
+      <li>
+        The World's Largest Radio Receiving Station. Owned by the Radio
+        Corporation of America at Rocky Point near Port Jefferson, L. I.
+      </li>
+      <li>
+        First Wireless College in the World, at Tufts College, Mass
+      </li>
+      <li>
+        Alexander Graham Bell, Inventor of the Telephone, now an ardent Radio
+        Enthusiast
+      </li>
+      <li>
+        World's Largest Loud Speaker ever made. Installed in Lytle Park,
+        Cincinnati, Ohio, to permit President Harding's Address at Point
+        Pleasant, Ohio, during the Grant Centenary Celebration to be heard
+        within a radius of one square
+      </li>
+      <li>
+        United States Naval High Power Station, Arlington, Va. General view of
+        Power Room. At the left can be seen the Control Switchboards, and
+        overhead, the great 30 K.W. Arc Transmitter with Accessories
+      </li>
+      <li>
+        The Transformer and Tuner of the World's Largest Radio Station. Owned by
+        the Radio Corporation of America at Rocky Point near Port Jefferson, L.
+        I.
+      </li>
+      <li>
+        Broadcasting Government Reports by Wireless from Washington. This shows
+        Mr. Gale at work with his set in the Post Office Department
+      </li>
+      <li>
+        Wireless Receptor, the size of a Safety Match Box. A Youthful Genius in
+        the person of Kenneth R. Hinman, who is only twelve years old, has made
+        a Wireless Receiving Set that fits neatly into a Safety Match Box. With
+        this Instrument and a Pair of Ordinary Receivers, he is able to catch
+        not only Code Messages but the regular Broadcasting Programs from
+        Stations Twenty and Thirty Miles Distant
+      </li>
+      <li>
+        Wireless Set made into a Ring, designed by Alfred G. Rinehart, of
+        Elizabeth, New Jersey. This little Receptor is a Practical Set; it will
+        receive Messages, Concerts, etc., measures 1" by 5/8" by 7/8". An
+        ordinary Umbrella is used as an Aerial
+      </li>
+    </ul>
+    <h2>
+      <a name="chap01" id="chap01">CHAPTER I</a>
+    </h2>
+    <h3>
+      HOW TO BEGIN WIRELESS
+    </h3>
+    <p>
+      In writing this book it is taken for granted that you are: <i>first</i>,
+      one of the several hundred thousand persons in the United States who are
+      interested in wireless telegraphy and telephony; <i>second</i>, that you
+      would like to install an apparatus in your home, and <i>third</i>, that it
+      is all new to you.
+    </p>
+    <p>
+      Now if you live in a city or town large enough to support an electrical
+      supply store, there you will find the necessary apparatus on sale, and
+      someone who can tell you what you want to know about it and how it works.
+      If you live away from the marts and hives of industry you can send to
+      various makers of wireless apparatus [Footnote: A list of makers of
+      wireless apparatus will be found in the <a href="#appendix">Appendix</a>.]
+      for their catalogues and price-lists and these will give you much useful
+      information. But in either case it is the better plan for you to know
+      before you start in to buy an outfit exactly what apparatus you need to
+      produce the result you have in mind, and this you can gain in easy steps
+      by reading this book.
+    </p>
+    <p>
+      <i>Kinds of Wireless Systems</i>.--There are two distinct kinds of
+      wireless systems and these are: the <i>wireless telegraph</i> system, and
+      the <i>wireless telephone</i> system. The difference between the wireless
+      telegraph and the wireless telephone is that the former transmits messages
+      by means of a <i>telegraph key</i>, and the latter transmits conversation
+      and music by means of a <i>microphone transmitter</i>. In other words, the
+      same difference exists between them in this respect as between the Morse
+      telegraph and the Bell telephone.
+    </p>
+    <p>
+      <i>Parts of a Wireless System</i>.--Every complete wireless station,
+      whether telegraph or telephone, consists of three chief separate and
+      distinct parts and these are: (<i>a</i>) the <i>aerial wire system</i>, or
+      <i>antenna</i> as it is often called, (<i>b</i>) the <i>transmitter</i>,
+      or <i>sender</i>, and (<i>c</i>) the <i>receiver</i>, or, more properly,
+      the <i>receptor</i>. The aerial wire is precisely the same for either
+      wireless telegraphy or wireless telephony. The transmitter of a wireless
+      telegraph set generally uses a <i>spark gap</i> for setting up the
+      electric oscillations, while usually for wireless telephony a <i>vacuum
+      tube</i> is employed for this purpose. The receptor for wireless
+      telegraphy and telephony is the same and may include either a <i>crystal
+      detector</i> or a <i>vacuum tube detector</i>, as will be explained
+      presently.
+    </p>
+    <p>
+      <i>The Easiest Way to Start.</i>--First of all you must obtain a
+      government license to operate a sending set, but you do not need a license
+      to put up and use a receiving set, though you are required by law to keep
+      secret any messages which you may overhear. Since no license is needed for
+      a receiving set the easiest way to break into the wireless game is to put
+      up an aerial and hook up a receiving set to it; you can then listen-in and
+      hear what is going on in the all-pervading ether around you, and you will
+      soon find enough to make things highly entertaining.
+    </p>
+    <p>
+      Nearly all the big wireless companies have great stations fitted with
+      powerful telephone transmitters and at given hours of the day and night
+      they send out songs by popular singers, dance music by jazz orchestras,
+      fashion talks by and for the ladies, agricultural reports, government
+      weather forecasts and other interesting features. Then by simply shifting
+      the slide on your tuning coil you can often tune-in someone who is sending
+      <i>Morse</i>, that is, messages in the dot and dash code, or, perhaps a
+      friend who has a wireless telephone transmitter and is talking. Of course,
+      if you want to <i>talk back</i> you must have a wireless transmitter,
+      either telegraphic or telephonic, and this is a much more expensive part
+      of the apparatus than the receptor, both in its initial cost and in its
+      operation. A wireless telegraph transmitter is less costly than a wireless
+      telephone transmitter and it is a very good scheme for you to learn to
+      send and receive telegraphic messages.
+    </p>
+    <p>
+      At the present time, however, there are fifteen amateur receiving stations
+      in the United States to every sending station, so you can see that the
+      majority of wireless folks care more for listening in to the broadcasting
+      of news and music than to sending out messages on their own account. The
+      easiest way to begin wireless, then, is to put up an aerial and hook up a
+      receiving set to it.
+    </p>
+    <p>
+      <i>About Aerial Wire Systems.</i>--To the beginner who wants to install a
+      wireless station the aerial wire system usually looms up as the biggest
+      obstacle of all, and especially is this true if his house is without a
+      flag pole, or other elevation from which the aerial wire can be
+      conveniently suspended.
+    </p>
+    <p>
+      If you live in the congested part of a big city where there are no yards
+      and, particularly, if you live in a flat building or an apartment house,
+      you will have to string your aerial wire on the roof, and to do this you
+      should get the owner's, or agent's, permission. This is usually an easy
+      thing to do where you only intend to receive messages, for one or two thin
+      wires supported at either end of the building are all that are needed. If
+      for any reason you cannot put your aerial on the roof then run a wire
+      along the building outside of your apartment, and, finally, if this is not
+      feasible, connect your receiver to a wire strung up in your room, or even
+      to an iron or a brass bed, and you can still get the near-by stations.
+    </p>
+    <p>
+      An important part of the aerial wire system is the <i>ground</i>, that is,
+      your receiving set must not only be connected with the aerial wire, but
+      with a wire that leads to and makes good contact with the moist earth of
+      the ground. Where a house or a building is piped for gas, water or steam,
+      it is easy to make a ground connection, for all you have to do is to
+      fasten the wire to one of the pipes with a clamp. [Footnote: Pipes are
+      often insulated from the ground, which makes them useless for this
+      purpose.] Where the house is isolated then a lot of wires or a sheet of
+      copper or of zinc must be buried in the ground at a sufficient depth to
+      insure their being kept moist.
+    </p>
+    <p>
+      <i>About the Receiving Apparatus</i>.--You can either buy the parts of the
+      receiving apparatus separate and hook them up yourself, or you can buy the
+      apparatus already assembled in a set which is, in the beginning, perhaps,
+      the better way.
+    </p>
+    <p>
+      The simplest receiving set consists of (1) a <i>detector</i>, (2) a <i>tuning
+      coil</i>, and (3) a <i>telephone receiver</i> and these three pieces of
+      apparatus are, of course, connected together and are also connected to the
+      aerial and ground as the diagram in <i>Fig. 1</i> clearly shows. There are
+      two chief kinds of detectors used at the present time and these are: (<i>a</i>)
+      the <i>crystal detector</i>, and (<i>b</i>) the <i>vacuum tube detector</i>.
+      The crystal detector is the cheapest and simplest, but it is not as
+      sensitive as the vacuum tube detector and it requires frequent adjustment.
+      A crystal detector can be used with or without a battery while the vacuum
+      tube detector requires two small batteries.
+    </p>
+    <p>
+      <a name="fig001" id="fig001"><img width="600" height="337"
+      src="images/fig001-002.jpg"
+      alt="Fig. 1.--Simple Receiving Set. Fig. 2.--Simple Transmitting Set." /></a>
+    </p>
+    <p>
+      A tuning coil of the simplest kind consists of a single layer of copper
+      wire wound on a cylinder with an adjustable, or sliding, contact, but for
+      sharp tuning you need a <i>loose coupled tuning coil</i>. Where a single
+      coil tuner is used a <i>fixed</i> condenser should be connected around the
+      telephone receivers. Where a loose coupled tuner is employed you should
+      have a variable condenser connected across the <i>closed oscillation
+      circuit</i> and a <i>fixed condenser</i> across the telephone receivers.
+    </p>
+    <p>
+      When listening-in to distant stations the energy of the received wireless
+      waves is often so very feeble that in order to hear distinctly an <i>amplifier</i>
+      must be used. To amplify the incoming sounds a vacuum tube made like a
+      detector is used and sometimes as many as half-a-dozen of these tubes are
+      connected in the receiving circuit, or in <i>cascade</i>, as it is called,
+      when the sounds are <i>amplified</i>, that is magnified, many hundreds of
+      times.
+    </p>
+    <p>
+      The telephone receiver of a receiving set is equally as important as the
+      detector. A single receiver can be used but a pair of receivers connected
+      with a head-band gives far better results. Then again the higher the
+      resistance of the receivers the more sensitive they often are and those
+      wound to as high a resistance as 3,200 ohms are made for use with the best
+      sets. To make the incoming signals, conversation or music, audible to a
+      room full of people instead of to just yourself you must use what is
+      called a <i>loud speaker</i>. In its simplest form this consists of a
+      metal cone like a megaphone to which is fitted a telephone receiver.
+    </p>
+    <p>
+      <i>About Transmitting Stations--Getting Your License.</i>--If you are
+      going to install a wireless sending apparatus, either telegraphic or
+      telephonic, you will have to secure a government license for which no fee
+      or charge of any kind is made. There are three classes of licenses issued
+      to amateurs who want to operate transmitting stations and these are: (1)
+      the <i>restricted amateur license</i>, (2) the <i>general amateur license</i>,
+      and (3) the <i>special amateur license</i>.
+    </p>
+    <p>
+      If you are going to set up a transmitter within five nautical miles of any
+      naval wireless station then you will have to get a <i>restricted amateur
+      license</i> which limits the current you use to half a <i>kilowatt</i>
+      [Footnote: A <i>Kilowatt</i> is 1,000 <i>watts</i>. There are 746 watts in
+      a horsepower.] and the wave length you send out to 200 <i>meters</i>.
+      Should you live outside of the five-mile range of a navy station then you
+      can get a general amateur license and this permits you to use a current of
+      1 kilowatt, but you are likewise limited to a wave length of 200 meters.
+      But if you can show that you are doing some special kind of wireless work
+      and not using your sending station for the mere pleasure you are getting
+      out of it you may be able to get a <i>special amateur license</i> which
+      gives you the right to send out wave lengths up to 375 meters.
+    </p>
+    <p>
+      When you are ready to apply for your license write to the <i>Radio
+      Inspector</i> of whichever one of the following districts you live in:
+    </p>
+<pre xml:space="preserve">
+  First District..............Boston, Mass.
+  Second   "    ..............New York City
+  Third    "    ..............Baltimore, Md.
+  Fourth   "    ..............Norfolk, Va.
+  Fifth    "    ..............New Orleans, La.
+  Sixth    "    ............. San Francisco, Cal.
+  Seventh  "    ............. Seattle, Wash.
+  Eighth   "    ............. Detroit, Mich.
+  Ninth    "    ..............Chicago, Ill.
+</pre>
+    <p>
+      <i>Kinds of Transmitters</i>.--There are two general types of transmitters
+      used for sending out wireless messages and these are: (1) <i>wireless
+      telegraph</i> transmitters, and (2) <i>wireless telephone</i>
+      transmitters. Telegraph transmitters may use either: (<i>a</i>) a <i>jump-spark</i>,
+      (<i>b</i>) an <i>electric arc</i>, or (<i>c</i>) a <i>vacuum tube</i>
+      apparatus for sending out dot and dash messages, while telephone
+      transmitters may use either, (<i>a</i>) an <i>electric arc</i>, or (<i>b</i>)
+      a <i>vacuum tube</i> for sending out vocal and musical sounds. Amateurs
+      generally use a <i>jump-spark</i> for sending wireless telegraph messages
+      and the <i>vacuum tube</i> for sending wireless telephone messages.
+    </p>
+    <p>
+      <i>The Spark Gap Wireless Telegraph Transmitter</i>.--The simplest kind of
+      a wireless telegraph transmitter consists of: (1) a <i>source of direct or
+      alternating current</i>, (2) a <i>telegraph key</i>, (3) a <i>spark-coil</i>
+      or a <i>transformer</i>, (4) a <i>spark gap</i>, (5) an <i>adjustable
+      condenser</i> and (6) an <i>oscillation transformer</i>. Where <i>dry
+      cells</i> or a <i>storage battery</i> must be used to supply the current
+      for energizing the transmitter a spark-coil can be employed and these may
+      be had in various sizes from a little fellow which gives 1/4-inch spark up
+      to a larger one which gives a 6-inch spark. Where more energy is needed it
+      is better practice to use a transformer and this can be worked on an
+      alternating current of 110 volts, or if only a 110 volt direct current is
+      available then an <i>electrolytic interrupter</i> must be used to make and
+      break the current. A simple transmitting set with an induction coil is
+      shown in <i>Fig. 2</i>.
+    </p>
+    <p>
+      A wireless key is made like an ordinary telegraph key except that where
+      large currents are to be used it is somewhat heavier and is provided with
+      large silver contact points. Spark gaps for amateur work are usually of:
+      (1) the <i>plain</i> or <i>stationary type</i>, (2) the <i>rotating type</i>,
+      and (3) the <i>quenched gap</i> type. The plain spark-gap is more suitable
+      for small spark-coil sets, and it is not so apt to break down the
+      transformer and condenser of the larger sets as the rotary gap. The rotary
+      gap on the other hand tends to prevent <i>arcing</i> and so the break is
+      quicker and there is less dragging of the spark. The quenched gap is more
+      efficient than either the plain or rotary gap and moreover it is
+      noiseless.
+    </p>
+    <p>
+      Condensers for spark telegraph transmitters can be ordinary Leyden jars or
+      glass plates coated with tin or copper foil and set into a frame, or they
+      can be built up of mica and sheet metal embedded in an insulating
+      composition. The glass plate condensers are the cheapest and will serve
+      your purpose well, especially if they are immersed in oil. Tuning coils,
+      sometimes called <i>transmitting inductances</i> and <i>oscillation
+      transformers</i>, are of various types. The simplest kind is a
+      transmitting inductance which consists of 25 or 30 turns of copper wire
+      wound on an insulating tube or frame. An oscillation transformer is a
+      loose coupled tuning coil and it consists of a primary coil formed of a
+      number of turns of copper wire wound on a fixed insulating support, and a
+      secondary coil of about twice the number of turns of copper wire which is
+      likewise fixed in an insulating support, but the coils are relatively
+      movable. An <i>oscillation transformer</i> (instead of a <i>tuning coil</i>),
+      is required by government regulations unless <i>inductively coupled</i>.
+    </p>
+    <p>
+      The <i>Vacuum Tube Telegraph Transmitter</i>.--This consists of: (1) a <i>source
+      of direct or alternating current</i>, (2) a <i>telegraph key</i>, (3) a <i>vacuum
+      tube oscillator</i>, (4) a <i>tuning coil</i>, and (5) a <i>condenser</i>.
+      This kind of a transmitter sets up <i>sustained</i> oscillations instead
+      of <i>periodic</i> oscillations which are produced by a spark gap set. The
+      advantages of this kind of a system will be found explained in <a
+      href="#chap16">Chapter XVI</a>.
+    </p>
+    <p>
+      <i>The Wireless Telephone Transmitter</i>.--Because a jump-spark sets up
+      <i>periodic oscillations</i>, that is, the oscillations are discontinuous,
+      it cannot be used for wireless telephony. An electric arc or a vacuum tube
+      sets up <i>sustained</i> oscillations, that is, oscillations which are
+      continuous. As it is far easier to keep the oscillations going with a
+      vacuum tube than it is with an arc the former means has all but supplanted
+      the latter for wireless telephone transmitters. The apparatus required and
+      the connections used for wireless telephone sets will be described in
+      later chapters.
+    </p>
+    <p>
+      <i>Useful Information</i>.--It would be wise for the reader to turn to the
+      <a href="#appendix">Appendix</a>, beginning with page 301 of this book,
+      and familiarize himself with the information there set down in tabular and
+      graphic form. For example, the first table gives abbreviations of
+      electrical terms which are in general use in all works dealing with the
+      subject. You will also find there brief definitions of electric and
+      magnetic units, which it would be well to commit to memory; or, at least,
+      to make so thoroughly your own that when any of these terms is mentioned,
+      you will know instantly what is being talked about.
+    </p>
+    <h2>
+      <a name="chap02" id="chap02">CHAPTER II</a>
+    </h2>
+    <h3>
+      PUTTING UP YOUR AERIAL
+    </h3>
+    <p>
+      As inferred in the first chapter, an aerial for receiving does not have to
+      be nearly as well made or put up as one for sending. But this does not
+      mean that you can slipshod the construction and installation of it, for
+      however simple it is, the job must be done right and in this case it is as
+      easy to do it right as wrong.
+    </p>
+    <p>
+      To send wireless telegraph and telephone messages to the greatest
+      distances and to receive them as distinctly as possible from the greatest
+      distances you must use for your aerial (1) copper or aluminum wire, (2)
+      two or more wires, (3) have them the proper length, (4) have them as high
+      in the air as you can, (5) have them well apart from each other, and (6)
+      have them well insulated from their supports. If you live in a flat
+      building or an apartment house you can string your aerial wires from one
+      edge of the roof to the other and support them by wooden stays as high
+      above it as may be convenient.
+    </p>
+    <p>
+      Should you live in a detached house in the city you can usually get your
+      next-door neighbor to let you fasten one end of the aerial to his house
+      and this will give you a good stretch and a fairly high aerial. In the
+      country you can stretch your wires between the house and barn or the
+      windmill. From this you will see that no matter where you live you can
+      nearly always find ways and means of putting up an aerial that will serve
+      your needs without going to the expense of erecting a mast.
+    </p>
+    <p>
+      <i>Kinds of Aerial Wire Systems</i>.--An amateur wireless aerial can be
+      anywhere from 25 feet to 100 feet long and if you can get a stretch of the
+      latter length and a height of from 30 to 75 feet you will have one with
+      which you can receive a thousand miles or more and send out as much energy
+      as the government will allow you to send.
+    </p>
+    <p>
+      The kind of an aerial that gives the best results is one whose wire, or
+      wires, are <i>horizontal</i>, that is, parallel with the earth under it as
+      shown at <i>A</i> in <i>Fig. 3.</i> If only one end can be fixed to some
+      elevated support then you can secure the other end to a post in the
+      ground, but the slope of the aerial should not be more than 30 or 35
+      degrees from the horizontal at most as shown at <i>B</i>.
+    </p>
+    <p>
+      <a name="fig003" id="fig003"><img width="600" height="262"
+      src="images/fig003.jpg"
+      alt="(A) Fig. 3.--Flat top, or Horizontal Aerial. (B) Fig. 3.--Inclined Aerial." />
+      </a>
+    </p>
+    <p>
+      The <i>leading-in wire</i>, that is, the wire that leads from and joins
+      the aerial wire with your sending and receiving set, can be connected to
+      the aerial anywhere it is most convenient to do so, but the best results
+      are had when it is connected to one end as shown at <i>A</i> in <i>Fig. 4</i>,
+      in which case it is called an <i>inverted L aerial</i>, or when it is
+      connected to it at the middle as shown at <i>B</i>, when it is called a <i>T
+      aerial</i>. The leading-in wire must be carefully insulated from the
+      outside of the building and also where it passes through it to the inside.
+      This is done by means of an insulating tube known as a <i>leading-in
+      insulator,</i> or <i>bulkhead insulator</i> as it is sometimes called.
+    </p>
+    <p>
+      <a name="fig004" id="fig004"><img width="532" height="160"
+      src="images/fig004.jpg"
+      alt="(A) Fig. 4.--Inverted L Aerial. (B) Fig. 4.--T Aerial." /></a>
+    </p>
+    <p>
+      As a protection against lightning burning out your instruments you can use
+      either: (1) an <i>air-gap lightning arrester,</i> (2) a <i>vacuum tube
+      protector,</i> or (3) a <i>lightning switch,</i> which is better.
+      Whichever of these devices is used it is connected in between the aerial
+      and an outside ground wire so that a direct circuit to the earth will be
+      provided at all times except when you are sending or receiving. So your
+      aerial instead of being a menace really acts during an electrical storm
+      like a lightning rod and it is therefore a real protection. The air-gap
+      and vacuum tube lightning arresters are little devices that can be used
+      only where you are going to receive, while the lightning switch must be
+      used where you are going to send; indeed, in some localities the <i>Fire
+      Underwriters</i> require a large lightning switch to be used for receiving
+      sets as well as sending sets.
+    </p>
+    <p>
+      <i>How to Put Up a Cheap Receiving Aerial.</i>--The kind of an aerial wire
+      system you put up will depend, chiefly, on two things, and these are: (1)
+      your pocketbook, and (2) the place where you live.
+    </p>
+    <p>
+      <i>A Single Wire Aerial.</i>--This is the simplest and cheapest kind of a
+      receiving aerial that can be put up. The first thing to do is to find out
+      the length of wire you need by measuring the span between the two points
+      of support; then add a sufficient length for the leading-in wire and
+      enough more to connect your receiving set with the radiator or water pipe.
+    </p>
+    <p>
+      You can use any size of copper or aluminum wire that is not smaller than
+      <i>No. 16 Brown and Sharpe gauge.</i> When you buy the wire get also the
+      following material: (1) two <i>porcelain insulators</i> as shown at <i>A</i>
+      in <i>Fig. 5</i>; (2) three or four <i>porcelain knob insulators</i>, see
+      <i>B</i>; (3) either (<i>a</i>) an <i>air gap lightning arrester,</i> see
+      <i>C</i>, or (<i>b</i>) a <i>lightning switch</i> see <i>D</i>; (4) a <i>leading-in
+      porcelain tube insulator,</i> see <i>E</i>, and (5) a <i>ground clamp</i>,
+      see <i>F</i>.
+    </p>
+    <p>
+      <a name="fig005" id="fig005"><img width="600" height="251"
+      src="images/fig005.jpg"
+      alt="Fig. 5.--Material for a Simple Aerial Wire System." /></a>
+    </p>
+    <p>
+      To make the aerial slip each end of the wire through a hole in each
+      insulator and twist it fast; next cut off and slip two more pieces of wire
+      through the other holes in the insulators and twist them fast and then
+      secure these to the supports at the ends of the building. Take the piece
+      you are going to use for the leading-in wire, twist it around the aerial
+      wire and solder it there when it will look like <i>A</i> in <i>Fig. 6</i>.
+      Now if you intend to use the <i>air gap lightning arrester</i> fasten it
+      to the wall of the building outside of your window, and bring the
+      leading-in wire from the aerial to the top binding post of your arrester
+      and keep it clear of everything as shown at <i>B</i>. If your aerial is on
+      the roof and you have to bring the leading-in wire over the cornice or
+      around a corner fix a porcelain knob insulator to the one or the other and
+      fasten the wire to it.
+    </p>
+    <p>
+      <a name="fig006a" id="fig006a"><img width="600" height="233"
+      src="images/fig006a.jpg"
+      alt="(A) Fig. 6.--Single Wire Aerial for Receiving." /></a> <a
+      name="fig006b" id="fig006b"><img width="600" height="711"
+      src="images/fig006b.jpg"
+      alt="(B) Fig. 6.--Receiving Aerial with Air Gap Lightning Arrester." /></a>
+      <a name="fig006c" id="fig006c"><img width="600" height="323"
+      src="images/fig006c.jpg" alt="(C) Fig. 6.--Aerial with Lightning Switch." /></a>
+    </p>
+    <p>
+      Next bore a hole through the frame of the window at a point nearest your
+      receiving set and push a porcelain tube 5/8 inch in diameter and 5 or 6
+      inches long, through it. Connect a length of wire to the top post of the
+      arrester or just above it to the wire, run this through the leading-in
+      insulator and connect it to the slider of your tuning coil. Screw the end
+      of a piece of heavy copper wire to the lower post of the arrester and run
+      it to the ground, on porcelain knobs if necessary, and solder it to an
+      iron rod or pipe which you have driven into the earth. Finally connect the
+      fixed terminal of your tuning coil with the water pipe or radiator inside
+      of the house by means of the ground clamp as shown in the diagrammatic
+      sketch at <i>B</i> in <i>Fig. 6</i> and you are ready to tune in.
+    </p>
+    <p>
+      If you want to use a lightning switch instead of the air-gap arrester then
+      fasten it to the outside wall instead of the latter and screw the free end
+      of the leading-in wire from the aerial to the middle post of it as shown
+      at <i>C</i> in <i>Fig. 6</i>. Run a wire from the top post through the
+      leading-in insulator and connect it with the slider of your tuning coil.
+      Next screw one end of a length of heavy copper wire to the lower post of
+      the aerial switch and run it to an iron pipe in the ground as described
+      above in connection with the spark-gap lightning arrester; then connect
+      the fixed terminal of your tuning coil with the radiator or water pipe and
+      your aerial wire system will be complete as shown at <i>C</i> in <i>Fig. 6</i>.
+    </p>
+    <p>
+      <i>A Two-wire Aerial.</i>--An aerial with two wires will give better
+      results than a single wire and three wires are better than two, but you
+      must keep them well apart. To put up a two-wire aerial get (1) enough <i>No.
+      16</i>, or preferably <i>No. 14</i>, solid or stranded copper or aluminum
+      wire, (2) four porcelain insulators, see <i>B</i> in <i>Fig. 5</i>, and
+      (3) two sticks about 1 inch thick, 3 inches wide and 3 or 4 feet long, for
+      the <i>spreaders</i>, and bore 1/8-inch hole through each end of each one.
+      Now twist the ends of the wires to the insulators and then cut off four
+      pieces of wire about 6 feet long and run them through the holes in the
+      wood spreaders. Finally twist the ends of each pair of short wires to the
+      free ends of the insulators and then twist the free ends of the wires
+      together.
+    </p>
+    <p>
+      For the leading-in wire that goes to the lightning switch take two lengths
+      of wire and twist one end of each one around the aerial wires and solder
+      them there. Twist the short wire around the long wire and solder this
+      joint also when the aerial will look like <i>Fig. 7</i>. Bring the free
+      end of the leading-in wire down to the middle post of the lightning switch
+      and fasten it there and connect up the receiver to it and the ground as
+      described under the caption of <i>A Single Wire Aerial</i>.
+    </p>
+    <p>
+      <a name="fig007" id="fig007"><img width="600" height="277"
+      src="images/fig007.jpg" alt="Fig. 7.--Two Wire Aerial." /></a>
+    </p>
+    <p>
+      <i>Connecting in the Ground.</i>--If there is a gas or water system or a
+      steam-heating plant in your house you can make your ground connection by
+      clamping a ground clamp to the nearest pipe as has been previously
+      described. Connect a length of bare or insulated copper wire with it and
+      bring this up to the table on which you have your receiving set. If there
+      are no grounded pipes available then you will have to make a good ground
+      which we shall describe presently and lead the ground wire from your
+      receiving set out of the window and down to it.
+    </p>
+    <p>
+      <i>How to Put Up a Good Aerial.</i>--While you can use the cheap aerial
+      already described for a small spark-coil sending set you should have a
+      better insulated one for a 1/2 or a 1 <i>kilowatt</i> transformer set. The
+      cost for the materials for a good aerial is small and when properly made
+      and well insulated it will give results that are all out of proportion to
+      the cost of it.
+    </p>
+    <p>
+      <i>An Inexpensive Good Aerial</i>.--A far better aerial, because it is
+      more highly insulated, can be made by using <i>midget insulators</i>
+      instead of the porcelain insulators described under the caption of <i>A
+      Single Wire Aerial</i> and using a small <i>electrose leading-in insulator</i>
+      instead of the porcelain bushing. This makes a good sending aerial for
+      small sets as well as a good receiving aerial.
+    </p>
+    <p>
+      <i>The Best Aerial that Can Be Made.</i>--To make this aerial get the
+      following material together: (1) enough <i>stranded or braided wire</i>
+      for three or four lengths of parallel wires, according to the number you
+      want to use (2) six or eight <i>electrose ball insulators</i>, see <i>B</i>,
+      <i>Fig. 8</i>; (3) two 5-inch or 10-inch <i>electrose strain insulators</i>,
+      see <i>C</i>; (4) six or eight <i>S-hooks</i>, <i>see D</i>; one large <i>withe</i>
+      with one eye for middle of end spreader, see <i>E</i>; (6) two smaller <i>withes</i>
+      with one eye each for end spreader, see <i>E</i>; (7) two still smaller <i>withes</i>,
+      with two eyes each for the ends of the end spreaders, see <i>E</i> (8) two
+      <i>thimbles</i>, see <i>F</i>, for 1/4-inch wire cable; (9) six or eight
+      <i>hard rubber tubes</i> or <i>bushings</i> as shown at <i>G</i>; and (10)
+      two <i>end spreaders</i>, see <i>H</i>; one <i>middle spreader, see I</i>;
+      and one <i>leading-in spreader</i>, see <i>J</i>.
+    </p>
+    <p>
+      <a name="fig008a" id="fig008a"><img width="595" height="480"
+      src="images/fig008a.jpg" alt="(A) Fig. 8--Part of a Good Aerial." /></a> <a
+      name="fig008b" id="fig008b"><img width="578" height="240"
+      src="images/fig008b.jpg" alt="(B) Fig. 8.--The Spreaders." /></a>
+    </p>
+    <p>
+      For this aerial any one of a number of kinds of wire can be used and among
+      these are (<i>a</i>) <i>stranded copper wire;</i> (<i>b</i>) <i>braided
+      copper wire;</i> (<i>c</i>) <i>stranded silicon bronze wire,</i> and (<i>d</i>)
+      <i>stranded phosphor bronze wire</i>. Stranded and braided copper wire is
+      very flexible as it is formed of seven strands of fine wire twisted or
+      braided together and it is very good for short and light aerials. Silicon
+      bronze wire is stronger than copper wire and should be used where aerials
+      are more than 100 feet long, while phosphor bronze wire is the strongest
+      aerial wire made and is used for high grade aerials by the commercial
+      companies and the Government for their high-power stations.
+    </p>
+    <p>
+      The spreaders should be made of spruce, and should be 4 feet 10 inches
+      long for a three-wire aerial and 7 feet 1 inch long for a four-wire aerial
+      as the distance between the wires should be about 27 inches. The end
+      spreaders can be turned cylindrically but it makes a better looking job if
+      they taper from the middle to the ends. They should be 2-1/4 inches in
+      diameter at the middle and 1-3/4 inches at the ends. The middle spreader
+      can be cylindrical and 2 inches in diameter. It must have holes bored
+      through it at equidistant points for the hard rubber tubes; each of these
+      should be 5/8 inch in diameter and have a hole 5/32 inch in diameter
+      through it for the aerial wire. The leading-in spreader is also made of
+      spruce and is 1-1/2 inches square and 26 inches long. Bore three or four
+      5/8-inch holes at equidistant points through this spreader and insert hard
+      rubber tubes in them as with the middle spreader.
+    </p>
+    <p>
+      <i>Assembling the Aerial.</i>--Begin by measuring off the length of each
+      wire to be used and see to it that all of them are of exactly the same
+      length. Now push the hard rubber insulators through the holes in the
+      middle spreader and thread the wires through the holes in the insulators
+      as shown at <i>A</i> in <i>Fig 9</i>.
+    </p>
+    <p>
+      Next twist the ends of each wire to the rings of the ball insulators and
+      then put the large withes on the middle of each of the end spreaders; fix
+      the other withes on the spreaders so that they will be 27 inches apart and
+      fasten the ball insulators to the eyes in the withes with the S-hooks. Now
+      slip a thimble through the eye of one of the long strain insulators,
+      thread a length of stranded steel wire 1/4 inch in diameter through it and
+      fasten the ends of it to the eyes in the withes on the ends of the
+      spreaders.
+    </p>
+    <p>
+      <a name="fig009ab" id="fig009ab"><img width="600" height="441"
+      src="images/fig009ab.jpg"
+      alt="(A) Fig. 9.--Middle Spreader. (B) Fig. 9.--One End of Aerial Complete." />
+      </a> <a name="fig009c" id="fig009c"><img width="600" height="422"
+      src="images/fig009c.jpg" alt="(C) Fig. 9.--Leading in Spreader." /></a>
+    </p>
+    <p>
+      Finally fasten a 40-inch length of steel stranded wire to each of the eyes
+      of the withes on the middle of each of the spreaders, loop the other end
+      over the thimble and then wrap the end around the wires that are fixed to
+      the ends of the spreaders. One end of the aerial is shown complete at <i>B</i>
+      in <i>Fig. 9</i>, and from this you can see exactly how it is assembled.
+      Now cut off three or four pieces of wire 15 or 20 feet long and twist and
+      solder each one to one of the aerial wires; then slip them through the
+      hard rubber tubes in the leading-in spreader, bring their free ends
+      together as at <i>C</i> and twist and solder them to a length of wire long
+      enough to reach to your lightning switch or instruments.
+    </p>
+    <p>
+      <i>Making a Good Ground</i>.--Where you have to make a <i>ground</i> you
+      can do so either by (1) burying sheets of zinc or copper in the moist
+      earth; (2) burying a number of wires in the moist earth, or (3) using a <i>counterpoise</i>.
+      To make a ground of the first kind take half a dozen large sheets of
+      copper or zinc, cut them into strips a foot wide, solder them all together
+      with other strips and bury them deeply in the ground.
+    </p>
+    <p>
+      It is easier to make a wire ground, say of as many or more wires as you
+      have in your aerial and connect them together with cross wires. To put
+      such a ground in the earth you will have to use a plow to make the furrows
+      deep enough to insure them always being moist. In the counterpoise ground
+      you make up a system of wires exactly like your aerial, that is, you
+      insulate them just as carefully; then you support them so that they will
+      be as close to the ground as possible and yet not touch it or anything
+      else. This and the other two grounds just described should be placed
+      directly under the aerial wire if the best results are to be had. In using
+      a counterpoise you must bring the wire from it up to and through another
+      leading-in insulator to your instruments.
+    </p>
+    <h2>
+      <a name="chap03" id="chap03">CHAPTER III</a>
+    </h2>
+    <h3>
+      SIMPLE TELEGRAPH AND TELEPHONE RECEIVING SETS
+    </h3>
+    <p>
+      With a crystal detector receiving set you can receive either telegraphic
+      dots and dashes or telephonic speech and music. You can buy a receiving
+      set already assembled or you can buy the different parts and assemble them
+      yourself. An assembled set is less bother in the beginning but if you like
+      to experiment you can <i>hook up</i>, that is, connect the separate parts
+      together yourself and it is perhaps a little cheaper to do it this way.
+      Then again, by so doing you get a lot of valuable experience in wireless
+      work and an understanding of the workings of wireless that you cannot get
+      in any other way.
+    </p>
+    <p>
+      <i>Assembled Wireless Receiving Sets</i>.--The cheapest assembled
+      receiving set [Footnote: The Marvel, made by the Radio Mfg. Co., New York
+      City.] advertised is one in which the detector and tuning coil is mounted
+      in a box. It costs $15.00, and can be bought of dealers in electric
+      supplies generally.
+    </p>
+    <p>
+      This price also includes a crystal detector, an adjustable tuning coil, a
+      single telephone receiver with head-band and the wire, porcelain
+      insulators, lightning switch and ground clamp for the aerial wire system.
+      It will receive wireless telegraph and telephone messages over a range of
+      from 10 to 25 miles.
+    </p>
+    <p>
+      Another cheap unit receptor, that is, a complete wireless receiving set
+      already mounted which can be used with a single aerial is sold for $25.00.
+      [Footnote: The Aeriola Jr., made by the Westinghouse Company, Pittsburgh,
+      Pa.] This set includes a crystal detector, a variable tuning coil, a fixed
+      condenser and a pair of head telephone receivers. It can also be used to
+      receive either telegraph or telephone messages from distances up to 25
+      miles. The aerial equipment is not included in this price, but it can be
+      bought for about $2.50 extra.
+    </p>
+    <p>
+      <i>Assembling Your Own Receiving Set</i>.--In this chapter we shall go
+      only into the apparatus used for two simple receiving sets, both of which
+      have a <i>crystal detector</i>. The first set includes a <i>double-slide
+      tuning coil</i> and the second set employs a <i>loose-coupled tuning coil</i>,
+      or <i>loose coupler</i>, as it is called for short. For either set you can
+      use a pair of 2,000- or 3,000-ohm head phones.
+    </p>
+    <table cellspacing="20" summary="Illustration">
+      <tr>
+        <td align="center">
+          <i>Photograph unavailable</i>
+        </td>
+      </tr>
+      <tr>
+        <td align="center">
+          original &copy; Underwood and Underwood.<br /> General Pershing
+          Listening In.
+        </td>
+      </tr>
+    </table>
+    <p>
+      <i>The Crystal Detector</i>.--A crystal detector consists of: (1) <i>the
+      frame</i>, (2) <i>the crystal</i>, and (3) <i>the wire point</i>. There
+      are any number of different designs for frames, the idea being to provide
+      a device that will (<i>a</i>) hold the sensitive crystal firmly in place,
+      and yet permit of its removal, (<i>b</i>) to permit the <i>wire point</i>,
+      or <i>electrode</i>, to be moved in any direction so that the free point
+      of it can make contact with the most sensitive spot on the crystal and (<i>c</i>)
+      to vary the pressure of the wire on the crystal.
+    </p>
+    <p>
+      A simple detector frame is shown in the cross-section at <i>A</i> in <i>Fig.
+      10</i>; the crystal, which may be <i>galena</i>, <i>silicon</i> or <i>iron
+      pyrites</i>, is held securely in a holder while the <i>phosphor-bronze
+      wire point</i> which makes contact with it, is fixed to one end of a
+      threaded rod on the other end of which is a knob. This rod screws into and
+      through a sleeve fixed to a ball that sets between two brass standards and
+      this permits an up and down or a side to side adjustment of the metal
+      point while the pressure of it on the crystal is regulated by the screw.
+    </p>
+    <p>
+      <a name="fig010ab" id="fig010ab"><img width="600" height="316"
+      src="images/fig010ab.jpg"
+      alt="(A) Fig. 10.--Cross Section of Crystal Detector. (B) Fig. 10.--The Crystal Detector Complete." />
+      </a>
+    </p>
+    <p>
+      A crystal of this kind is often enclosed in a glass cylinder and this
+      makes it retain its sensitiveness for a much longer time than if it were
+      exposed to dust and moisture. An upright type of this detector can be
+      bought for $2.25, while a horizontal type, as shown at <i>B</i>, can be
+      bought for $2.75. Galena is the crystal that is generally used, for, while
+      it is not quite as sensitive as silicon and iron pyrites, it is easier to
+      obtain a sensitive piece.
+    </p>
+    <p>
+      <i>The Tuning Coil</i>.--It is with the tuning coil that you <i>tune in</i>
+      and <i>tune out</i> different stations and this you do by sliding the
+      contacts to and fro over the turns of wire; in this way you vary the <i>inductance</i>
+      and <i>capacitance</i>, that is, the <i>constants</i> of the receiving
+      circuits and so make them receive <i>electric waves</i>, that is, wireless
+      waves, of different lengths.
+    </p>
+    <p>
+      <i>The Double Slide Tuning Coil</i>.--With this tuning coil you can
+      receive waves from any station up to 1,000 meters in length. One of the
+      ends of the coil of wire connects with the binding post marked <i>a</i> in
+      <i>Fig. 11</i>, and the other end connects with the other binding post
+      marked <i>b</i>, while one of the sliding contacts is connected to the
+      binding post <i>c</i>, and the <i>other sliding contact</i> is connected
+      with the binding post <i>d</i>.
+    </p>
+    <p>
+      <a name="fig011ab" id="fig011ab"><img width="600" height="234"
+      src="images/fig011ab.jpg"
+      alt="(A) Fig. 11.--Schematic Diagram of Double Slide Tuning Coil. (B) Fig. 11.--Double Slide Tuning Coil Complete." />
+      </a>
+    </p>
+    <p>
+      When connecting in the tuning coil, only the post <i>a</i> or the post <i>b</i>
+      is used as may be most convenient, but the other end of the wire which is
+      connected to a post is left free; just bear this point in mind when you
+      come to connect the tuning coil up with the other parts of your receiving
+      set. The tuning coil is shown complete at <i>B</i> and it costs $3.00 or
+      $4.00. A <i>triple slide</i> tuning coil constructed like the double slide
+      tuner just described, only with more turns of wire on it, makes it
+      possible to receive wave lengths up to 1,500 meters. It costs about $6.00.
+    </p>
+    <p>
+      <i>The Loose Coupled Tuning Coil</i>.--With a <i>loose coupler</i>, as
+      this kind of a tuning coil is called for short, very <i>selective tuning</i>
+      is possible, which means that you can tune in a station very sharply, and
+      it will receive any wave lengths according to size of coils. The primary
+      coil is wound on a fixed cylinder and its inductance is varied by means of
+      a sliding contact like the double slide tuning coil described above. The
+      secondary coil is wound on a cylinder that slides in and out of the
+      primary coil. The inductance of this coil is varied by means of a switch
+      that makes contact with the fixed points, each of which is connected with
+      every twentieth turn of wire as shown in the diagram <i>A</i> in <i>Fig.
+      12</i>. The loose coupler, which is shown complete at <i>B</i>, costs in
+      the neighborhood of $8.00 or $10.00.
+    </p>
+    <p>
+      <a name="fig012ab" id="fig012ab"><img width="600" height="326"
+      src="images/fig012ab.jpg"
+      alt="(A) Fig. 12.--Schematic Diagram of Loose Coupler. (B) Fig. 12.--Loose Coupler Complete." />
+      </a>
+    </p>
+    <p>
+      <i>Fixed and Variable Condensers</i>.--You do not require a condenser for
+      a simple receiving set, but if you will connect a <i>fixed condenser</i>
+      across your headphones you will get better results, while a <i>variable
+      condenser</i> connected in the <i>closed circuit of a direct coupled
+      receiving set</i>, that is, one where a double slide tuning coil is used,
+      makes it easy to tune very much more sharply; a variable condenser is
+      absolutely necessary where the circuits are <i>inductively coupled</i>,
+      that is, where a loose coupled tuner is used.
+    </p>
+    <p>
+      A fixed condenser consists of a number of sheets of paper with leaves of
+      tin-foil in between them and so built up that one end of every other leaf
+      of tin-foil projects from the opposite end of the paper as shown at <i>A</i>
+      in <i>Fig. 13</i>. The paper and tin-foil are then pressed together and
+      impregnated with an insulating compound. A fixed condenser of the exact
+      capacitance required for connecting across the head phones is mounted in a
+      base fitted with binding posts, as shown at <i>B</i>, and costs 75 cents.
+      (Paper ones 25 cents.)
+    </p>
+    <p>
+      <a name="fig013ab" id="fig013ab"><img width="593" height="240"
+      src="images/fig013ab.jpg"
+      alt="(A) Fig. 13.--How a Fixed Receiving Condenser is Built up. (B) Fig. 13.--The Fixed Condenser Complete." />
+      </a> <a name="fig013cd" id="fig013cd"><img width="584" height="280"
+      src="images/fig013cd.jpg"
+      alt="(C) and (D) Fig. 13.--The Variable Rotary Condenser." /></a>
+    </p>
+    <p>
+      A variable condenser, see <i>C</i>, of the rotating type is formed of a
+      set of fixed semi-circular metal plates which are slightly separated from
+      each other and between these a similar set of movable semi-circular metal
+      plates is made to interleave; the latter are secured to a shaft on the top
+      end of which is a knob and by turning it the capacitance of the condenser,
+      and, hence, of the circuit in which it is connected, is varied. This
+      condenser, which is shown at <i>D</i>, is made in two sizes, the smaller
+      one being large enough for all ordinary wave lengths while the larger one
+      is for proportionately longer wave lengths. These condensers cost $4.00
+      and $5.00 respectively.
+    </p>
+    <p>
+      <i>About Telephone Receivers.</i>--There are a number of makes of head
+      telephone receivers on the market that are designed especially for
+      wireless work. These phones are wound to <i>resistances</i> of from 75 <i>ohms</i>
+      to 8,000 <i>ohms</i>, and cost from $1.25 for a receiver without a cord or
+      headband to $15.00 for a pair of phones with a cord and head band. You can
+      get a receiver wound to any resistance in between the above values but for
+      either of the simple receiving sets such as described in this chapter you
+      ought to have a pair wound to at least 2,000 ohms and these will cost you
+      about $5.00. A pair of head phones of this type is shown in <i>Fig. 14.</i>
+    </p>
+    <p>
+      <a name="fig014" id="fig014"><img width="389" height="400"
+      src="images/fig014.jpg" alt="Fig. 14.--Pair of Wireless Head Phones." /></a>
+    </p>
+    <p>
+      <i>Connecting Up the Parts</i>--<i>Receiving Set No. 1.</i>--For this set
+      get (1) a <i>crystal detector</i>, (2) a <i>two-slide tuning coil</i>, (3)
+      a <i>fixed condenser</i>, and (4) a pair of 2,000 ohm head phones. Mount
+      the detector on the right-hand side of a board and the tuning coil on the
+      left-hand side. Screw in two binding posts for the cord ends of the
+      telephone receivers at <i>a</i> and <i>b</i> as shown at <i>A</i> in <i>Fig.
+      15</i>. This done connect one of the end binding posts of the tuning coil
+      with the ground wire and a post of one of the contact slides with the
+      lightning arrester or switch which leads to the aerial wire.
+    </p>
+    <p>
+      <a name="fig015a" id="fig015a"><img width="600" height="526"
+      src="images/fig015a.jpg"
+      alt="Fig. 15.--Top View of Apparatus Layout for Receiving Set No. 1." /></a>
+      <a name="fig015b" id="fig015b"><img width="516" height="520"
+      src="images/fig015b.jpg"
+      alt="(B) Fig. 15.--Wiring Diagram for Receiving Set No. 1." /></a>
+    </p>
+    <p>
+      Now connect the post of the other contact slide to one of the posts of the
+      detector and the other post of the latter with the binding post <i>a</i>,
+      then connect the binding post <i>b</i> to the ground wire and solder the
+      joint. Next connect the ends of the telephone receiver cord to the posts
+      <i>a</i> and <i>b</i> and connect a fixed condenser also with these posts,
+      all of which are shown in the wiring diagram at <i>B</i>, and you are
+      ready to adjust the set for receiving.
+    </p>
+    <p>
+      <i>Receiving Set No. 2.</i>--Use the same kind of a detector and pair of
+      head phones as for <i>Set No. 1</i>, but get (1) a <i>loose coupled tuning
+      coil</i>, and (2) a <i>variable condenser</i>. Mount the loose coupler at
+      the back of a board on the left-hand side and the variable condenser on
+      the right-hand side. Then mount the detector in front of the variable
+      condenser and screw two binding posts, <i>a</i> and <i>b</i>, in front of
+      the tuning coil as shown at <i>A</i> in <i>Fig. 16</i>.
+    </p>
+    <p>
+      <a name="fig016a" id="fig016a"><img width="600" height="598"
+      src="images/fig016a.jpg"
+      alt="Fig. 16.--Top view of Apparatus Layout for Receiving Set No. 2." /></a>
+      <a name="fig016b" id="fig016b"><img width="600" height="485"
+      src="images/fig016b.jpg"
+      alt="(B) Fig. 16.--Wiring Diagram for Receiving Set No. 2." /></a>
+    </p>
+    <p>
+      Now connect the post of the sliding contact of the loose coupler with the
+      wire that runs to the lightning switch and thence to the aerial; connect
+      the post of the primary coil, which is the outside coil, with the ground
+      wire; then connect the binding post leading to the switch of the secondary
+      coil, which is the inside coil, with one of the posts of the variable
+      condenser, and finally, connect the post that is joined to one end of the
+      secondary coil with the other post of the variable condenser.
+    </p>
+    <p>
+      This done, connect one of the posts of the condenser with one of the posts
+      of the detector, the other post of the detector with the binding post <i>a</i>,
+      and the post <i>b</i> to the other post of the variable condenser. Next
+      connect a fixed condenser to the binding posts <i>a</i> and <i>b</i> and
+      then connect the telephone receivers to these same posts, all of which is
+      shown in the wiring diagram at <i>B</i>. You are now ready to adjust the
+      instruments. In making the connections use No. 16 or 18 insulated copper
+      wire and scrape the ends clean where they go into the binding posts. See,
+      also, that all of the connections are tight and where you have to cross
+      the wires keep them apart by an inch or so and always cross them at right
+      angles.
+    </p>
+    <p>
+      <i>Adjusting the No. 1 Set</i>--<i>The Detector.</i>--The first thing to
+      do is to test the detector in order to find out if the point of the
+      contact wire is on a sensitive spot of the crystal. To do this you need a
+      <i>buzzer</i>, a <i>switch</i> and a <i>dry cell</i>. An electric bell
+      from which the gong has been removed will do for the buzzer, but you can
+      get one that is made specially for the purpose, for 75 cents, which gives
+      out a clear, high-pitched note that sounds like a high-power station.
+    </p>
+    <p>
+      Connect one of the binding posts of the buzzer with one post of the
+      switch, the other post of the latter with the zinc post of the dry cell
+      and the carbon post of this to the other post of the buzzer. Then connect
+      the post of the buzzer that is joined to the vibrator, to the ground wire
+      as shown in the wiring diagram, <i>Fig. 17.</i> Now close the switch of
+      the buzzer circuit, put on your head phones, and move the wire point of
+      the detector to various spots on the crystal until you hear the sparks
+      made by the buzzer in your phones.
+    </p>
+    <p>
+      <a name="fig017" id="fig017"><img width="434" height="640"
+      src="images/fig017.jpg" alt="Fig. 17.--Adjusting the Receiving Set." /></a>
+    </p>
+    <p>
+      Then vary the pressure of the point on the crystal until you hear the
+      sparks as loud as possible. After you have made the adjustment open the
+      switch and disconnect the buzzer wire from the ground wire of your set.
+      This done, be very careful not to jar the detector or you will throw it
+      out of adjustment and then you will have to do it all over again. You are
+      now ready to tune the set with the tuning coil and listen in.
+    </p>
+    <p>
+      <i>The Tuning Coil.</i>--To tune this set move the slide <i>A</i> of the
+      double-slide tuner, see <i>B</i> in <i>Fig. 15</i>, over to the end of the
+      coil that is connected with the ground wire and the slide <i>B</i> near
+      the opposite end of the coil, that is, the one that has the free end. Now
+      move the slide <i>A</i> toward the <i>B</i> slide and when you hear the
+      dots and dashes, or speech or music, that is coming in as loud as you can
+      move the <i>B</i> slide toward the <i>A</i> slide until you hear still
+      more loudly. A very few trials on your part and you will be able to tune
+      in or tune out any station you can hear, if not too close or powerful.
+    </p>
+    <table cellspacing="20" summary="Illustration">
+      <tr>
+        <td align="center">
+          <i>Photograph unavailable</i>
+        </td>
+      </tr>
+      <tr>
+        <td align="center">
+          original &copy; Underwood and Underwood.<br /> The World's Largest
+          Radio Receiving Station. Owned by the Radio Corporation of America at
+          Rocky Point near Point Jefferson, L.I.
+        </td>
+      </tr>
+    </table>
+    <p>
+      <i>Adjusting the No. 2 Set.</i>--First adjust the crystal detector with
+      the buzzer set as described above with <i>Set No. 1,</i> then turn the
+      knob of your variable condenser so that the movable plates are just
+      half-way in, pull the secondary coil of your loose-coupled tuner half way
+      out; turn the switch lever on it until it makes a contact with the middle
+      contact point and set the slider of the primary coil half way between the
+      ends.
+    </p>
+    <p>
+      Now listen in for telegraphic signals or telephonic speech or music; when
+      you hear one or the other slide the secondary coil in and out of the
+      primary coil until the sounds are loudest; now move the contact switch
+      over the points forth and back until the sounds are still louder, then
+      move the slider to and fro until the sounds are yet louder and, finally,
+      turn the knob of the condenser until the sounds are clear and crisp. When
+      you have done all of these things you have, in the parlance of the
+      wireless operator, <i>tuned in</i> and you are ready to receive whatever
+      is being sent.
+    </p>
+    <h2>
+      <a name="chap04" id="chap04">CHAPTER IV</a>
+    </h2>
+    <h3>
+      SIMPLE TELEGRAPH SENDING SETS
+    </h3>
+    <p>
+      A wireless telegraph transmitting set can be installed for a very small
+      amount of money provided you are content with one that has a limited
+      range. Larger and better instruments can, of course, be had for more
+      money, but however much you are willing to spend still you are limited in
+      your sending radius by the Government's rules and regulations. The best
+      way, and the cheapest in the end, to install a telegraph set is to buy the
+      separate parts and hook them up yourself.
+    </p>
+    <p>
+      The usual type of wireless telegraph transmitter employs a <i>disruptive
+      discharge,</i> or <i>spark,</i> as it is called, for setting up the
+      oscillating currents in the aerial wire system and this is the type of
+      apparatus described in this chapter. There are two ways to set up the
+      sparks and these are: (1) with an <i>induction coil,</i> or <i>spark-coil,</i>
+      as it is commonly called, and (2) with an <i>alternating current
+      transformer</i>, or <i>power transformer</i>, as it is sometimes called.
+      Where you have to generate the current with a battery you must use a spark
+      coil, but if you have a 110-volt direct or alternating lighting current in
+      your home you can use a transformer which will give you more power.
+    </p>
+    <p>
+      <i>A Cheap Transmitting Set (No. 1)</i>.--For this set you will need: (1)
+      a <i>spark-coil</i>, (2) a <i>battery</i> of dry cells, (3) a <i>telegraph
+      key</i>, (4) a <i>spark gap</i>, (5) a <i>high-tension condenser</i>, and
+      (6) an <i>oscillation transformer</i>. There are many different makes and
+      styles of these parts but in the last analysis all of them are built on
+      the same underlying bases and work on the same fundamental principles.
+    </p>
+    <p>
+      <i>The Spark-Coil</i>.--Spark coils for wireless work are made to give
+      sparks from 1/4 inch in length up to 6 inches in length, but as a spark
+      coil that gives less than a 1-inch spark has a very limited output it is
+      best to get a coil that gives at least a 1-inch spark, as this only costs
+      about $8.00, and if you can get a 2- or a 4-inch spark coil so much the
+      better. There are two general styles of spark coils used for wireless and
+      these are shown at <i>A</i> and <i>B</i> in <i>Fig. 18</i>.
+    </p>
+    <p>
+      <a name="fig018ab" id="fig018ab"><img width="600" height="276"
+      src="images/fig018ab.jpg"
+      alt="(A) and (B) Fig. 18.--Types of Spark Coils for Set. No. 1." /></a> <a
+      name="fig018c" id="fig018c"><img width="600" height="435"
+      src="images/fig018c.jpg" alt="(C) Fig. 18.--Wiring Diagram of Spark Coil" /></a>
+    </p>
+    <p>
+      A spark coil of either style consists of (<i>a</i>) a soft <i>iron core</i>
+      on which is wound (<i>b</i>) a couple of layers of heavy insulated wire
+      and this is called the <i>primary coil</i>, (<i>c</i>) while over this,
+      but insulated from it, is wound a large number of turns of very fine
+      insulated copper wire called the <i>secondary coil</i>; (<i>d</i>) an <i>interrupter</i>,
+      or <i>vibrator</i>, as it is commonly called, and, finally, (<i>e</i>) a
+      <i>condenser</i>. The core, primary and secondary coils form a unit and
+      these are set in a box or mounted on top of a hollow wooden base. The
+      condenser is placed in the bottom of the box, or on the base, while the
+      vibrator is mounted on one end of the box or on top of the base, and it is
+      the only part of the coil that needs adjusting.
+    </p>
+    <p>
+      The vibrator consists of a stiff, flat spring fixed at one end to the box
+      or base while it carries a piece of soft iron called an <i>armature</i> on
+      its free end and this sets close to one end of the soft iron core.
+      Insulated from this spring is a standard that carries an adjusting screw
+      on the small end of which is a platinum point and this makes contact with
+      a small platinum disk fixed to the spring. The condenser is formed of
+      alternate sheets of paper and tinfoil built up in the same fashion as the
+      receiving condenser described under the caption of <i>Fixed and Variable
+      Condensers</i>, in <a href="#chap03">Chapter III</a>.
+    </p>
+    <p>
+      The wiring diagram <i>C</i> shows how the spark coil is wired up. One of
+      the battery binding posts is connected with one end of the primary coil
+      while the other end of the latter which is wound on the soft iron core
+      connects with the spring of the vibrator. The other battery binding post
+      connects with the standard that supports the adjusting screw. The
+      condenser is shunted across the vibrator, that is, one end of the
+      condenser is connected with the spring and the other end of the condenser
+      is connected with the adjusting screw standard. The ends of the secondary
+      coil lead to two binding posts, which are usually placed on top of the
+      spark coil and it is to these that the spark gap is connected.
+    </p>
+    <p>
+      <i>The Battery.</i>--This can be formed of dry cells or you can use a
+      storage battery to energize your coil. For all coils that give less than a
+      1-inch spark you should use 5 dry cells; for 1-and 2-inch spark coils use
+      6 or 8 dry cells, and for 3 to 4-inch spark coils use 8 to 10 dry cells.
+      The way the dry cells are connected together to form a battery will be
+      shown presently. A dry cell is shown at <i>A</i> in <i>Fig, 19</i>.
+    </p>
+    <p>
+      <a name="fig019" id="fig019"><img width="600" height="389"
+      src="images/fig019.jpg"
+      alt="Fig. 19.--Other parts for Transmitting Set No. 1" /></a>
+    </p>
+    <p>
+      <i>The Telegraph Key.</i>--You can use an ordinary Morse telegraph key for
+      the sending set and you can get one with a japanned iron base for $1.50
+      (or better, one made of brass and which has 1/8-inch silver contact points
+      for $3.00. A key of the latter kind is shown at <i>B</i>).
+    </p>
+    <p>
+      <i>The Spark gap.</i>--It is in the <i>spark gap</i> that the high tension
+      spark takes place. The apparatus in which the spark takes place is also
+      called the <i>spark gap</i>. It consists of a pair of zinc plugs, called
+      <i>electrodes</i>, fixed to the ends of a pair of threaded rods, with
+      knobs on the other ends, and these screw into and through a pair of
+      standards as shown at <i>c</i>. This is called a <i>fixed</i>, or <i>stationary
+      spark gap</i> and costs about $1.00.
+    </p>
+    <p>
+      <i>The Tuning Coil.</i>--The <i>transmitting inductance</i>, or <i>sending
+      tuning coil</i>, consists of 20 to 30 turns of <i>No. 8 or 9</i> hard
+      drawn copper wire wound on a slotted insulated form and mounted on a
+      wooden base. It is provided with <i>clips</i> so that you can cut in and
+      cut out as many turns of wire as you wish and so tune the sending circuits
+      to send out whatever wave length you desire. It is shown at <i>d</i>, and
+      costs about $5.00. See also <i>Oscillation Transformer</i>, page 63
+      [Chapter IV].
+    </p>
+    <p>
+      <i>The High Tension Condenser.</i>--High tension condensers, that is,
+      condensers which will stand up under <i>high potentials</i>, or electric
+      pressures, can be bought in units or sections. These condensers are made
+      up of thin brass plates insulated with a special compound and pressed into
+      a compact form. The <i>capacitance</i> [Footnote: This is the capacity of
+      the condenser.] of one section is enough for a transmitting set using a
+      spark coil that gives a 2 inch spark or less and two sections connected
+      together should be used for coils giving from 2 to 4 inch sparks. It is
+      shown at <i>e</i>.
+    </p>
+    <p>
+      <i>Connecting Up the Apparatus</i>.--Your sending set should be mounted on
+      a table, or a bench, where it need not be moved. Place the key in about
+      the middle of the table and down in front, and the spark coil to the left
+      and well to the back but so that the vibrator end will be to the right, as
+      this will enable you to adjust it easily. Place the battery back of the
+      spark coil and the tuning coil (oscillation transformer) to the right of
+      the spark coil and back of the key, all of which is shown in the layout at
+      <i>A</i> in <i>Fig. 20</i>.
+    </p>
+    <p>
+      <a name="fig020a" id="fig020a"><img width="600" height="549"
+      src="images/fig020a.jpg"
+      alt="(A) Fig. 20.--Top View of Apparatus Layout for Sending Set No. 1." /></a>
+      <a name="fig020b" id="fig020b"><img width="600" height="437"
+      src="images/fig020b.jpg"
+      alt="(B) Fig. 20.--Wiring of Diagram for Sending Set No. 1." /></a>
+    </p>
+    <p>
+      For the <i>low voltage circuit</i>, that is the battery circuit, use <i>No.
+      12</i> or <i>14</i> insulated copper wire. Connect all of the dry cells
+      together in <i>series</i>, that is, connect the zinc of one cell with the
+      carbon of the next and so on until all of them are connected up. Then
+      connect the carbon of the end cell with one of the posts of the key, the
+      zinc of the other end cell with one of the primary posts of the spark coil
+      and the other primary post of the spark coil with the other post of the
+      key, when the primary circuit will be complete.
+    </p>
+    <p>
+      For the <i>high tension circuits</i>, that is, the <i>oscillation circuits</i>,
+      you may use either bare or insulated copper wire but you must be careful
+      that they do not touch the table, each other, or any part of the
+      apparatus, except, of course, the posts they are connected with. Connect
+      one of the posts of the secondary coil of the spark coil with one of the
+      posts of the spark gap, and the other post with one of the posts of the
+      condenser; then connect the other post of the condenser with the lower
+      spring clip of the tuning coil and also connect this clip with the ground.
+      This done, connect the middle spring clip with one of the posts of the
+      spark gap, and, finally, connect the top clip with the aerial wire and
+      your transmitting set is ready to be tuned. A wiring diagram of the
+      connections is shown at <i>B</i>. As this set is tuned in the same way as
+      <i>Set No. 2</i> which follows, you are referred to the end of this
+      chapter.
+    </p>
+    <p>
+      <i>A Better Transmitting Set (No. 2).</i>--The apparatus for this set
+      includes: (1) an <i>alternating current transformer</i>, (2) a <i>wireless
+      telegraph key</i>, (3) a <i>fixed</i>, a <i>rotary</i>, or a <i>quenched
+      spark gap</i>, (4) a <i>condenser</i>, and (5) an <i>oscillation
+      transformer</i>. If you have a 110 volt direct lighting current in your
+      home instead of 110 volt alternating current, then you will also need (6)
+      an <i>electrolytic interrupter</i>, for in this case the primary circuit
+      of the transformer must be made and broken rapidly in order to set up
+      alternating currents in the secondary coil.
+    </p>
+    <p>
+      <i>The Alternating Current Transformer.</i>--An alternating current, or
+      power, transformer is made on the same principle as a spark coil, that is,
+      it has a soft iron core, a primary coil formed of a couple of layers of
+      heavy wire, and a secondary coil wound up of a large number of turns of
+      very fine wire. Unlike the spark coil, however, which has an <i>open
+      magnetic core</i> and whose secondary coil is wound on the primary coil,
+      the transformer has a <i>closed magnetic core</i>, with the primary coil
+      wound on one of the legs of the core and the secondary wound on the other
+      leg. It has neither a vibrator nor a condenser. A plain transformer is
+      shown at <i>A</i> in <i>Fig. 21</i>.
+    </p>
+    <p>
+      <a name="fig021" id="fig021"><img width="600" height="584"
+      src="images/fig021.jpg" alt="Fig. 21.--Parts for Transmitting Set No. 2." /></a>
+    </p>
+    <p>
+      A transformer of this kind can be bought either (a) <i>unmounted</i>, that
+      is, just the bare transformer, or (b) <i>fully mounted</i>, that is,
+      fitted with an iron stand, mounted on an insulating base on which are a
+      pair of primary binding posts, while the secondary is provided with a <i>safety
+      spark gap</i>. There are three sizes of transformers of this kind made and
+      they are rated at 1/4, 1/2 and 1 kilowatt, respectively, they deliver a
+      secondary current of 9,000, 11,000 and 25,000 volts, according to size,
+      and cost $16.00, $22.00 and $33.00 when fully mounted; a reduction of
+      $3.00, $4.00 and $5.00 is made when they are unmounted. All of these
+      transformers operate on 110 volt, 60 cycle current and can be connected
+      directly to the source of alternating current.
+    </p>
+    <p>
+      <i>The Wireless Key</i>.--For this transmitting set a standard wireless
+      key should be used as shown at <i>B</i>. It is made about the same as a
+      regular telegraph key but it is much heavier, the contact points are
+      larger and instead of the current being led through the bearings as in an
+      ordinary key, it is carried by heavy conductors directly to the contact
+      points. This key is made in three sizes and the first will carry a current
+      of 5 <i>amperes</i> [Footnote: See <a href="#appendix">Appendix</a> for
+      definition.] and costs $4.00, the second will carry a current of 10
+      amperes and costs $6.50, while the third will carry a current of 20
+      amperes and costs $7.50.
+    </p>
+    <p>
+      <i>The Spark Gap.</i>--Either a fixed, a rotary, or a quenched spark gap
+      can be used with this set, but the former is seldom used except with
+      spark-coil sets, as it is very hard to keep the sparks from arcing when
+      large currents are used. A rotary spark gap comprises a wheel, driven by a
+      small electric motor, with projecting plugs, or electrodes, on it and a
+      pair of stationary plugs on each side of the wheel as shown at <i>C</i>.
+      The number of sparks per second can be varied by changing the speed of the
+      wheel and when it is rotated rapidly it sends out signals of a high pitch
+      which are easy to read at the receiving end. A rotary gap with a 110-volt
+      motor costs about $25.00.
+    </p>
+    <p>
+      A quenched spark gap not only eliminates the noise of the ordinary gap
+      but, when properly designed, it increases the range of an induction coil
+      set some 200 per cent. A 1/4 kilowatt quenched gap costs $10.00.
+      [Footnote: See <a href="#appendix">Appendix</a> for definition.]
+    </p>
+    <p>
+      <i>The High Tension Condenser</i>.--Since, if you are an amateur, you can
+      only send out waves that are 200 meters in length, you can only use a
+      condenser that has a capacitance of .007 <i>microfarad</i>. [Footnote: See
+      <a href="#appendix">Appendix</a> for definition.] A sectional high tension
+      condenser like the one described in connection with <i>Set No. 1</i> can
+      be used with this set but it must have a capacitance of not more than .007
+      microfarad. A condenser of this value for a 1/4-kilowatt transformer costs
+      $7.00; for a 1/2-kilowatt transformer $14.00, and for a 1-kilowatt
+      transformer $21.00. See <i>E, Fig. 19</i>.
+    </p>
+    <p>
+      <i>The Oscillation Transformer</i>.--With an oscillation transformer you
+      can tune much more sharply than with a single inductance coil tuner. The
+      primary coil is formed of 6 turns of copper strip, or No. 9 copper wire,
+      and the secondary is formed of 9 turns of strip, or wire. The primary
+      coil, which is the outside coil, is hinged to the base and can be raised
+      or lowered like the lid of a box. When it is lowered the primary and
+      secondary coils are in the same plane and when it is raised the coils set
+      at an angle to each other. It is shown at <i>D</i> and costs $5.00.
+    </p>
+    <p>
+      <i>Connecting Up the Apparatus. For Alternating Current.</i>--Screw the
+      key to the table about the middle of it and near the front edge; place the
+      high tension condenser back of it and the oscillation transformer back of
+      the latter; set the alternating current transformer to the left of the
+      oscillation transformer and place the rotary or quenched spark gap in
+      front of it.
+    </p>
+    <p>
+      Now bring a pair of <i>No. 12</i> or <i>14</i> insulated wires from the
+      110 volt lighting leads and connect them with a single-throw, double-pole
+      switch; connect one pole of the switch with one of the posts of the
+      primary coil of the alternating power transformer and connect the other
+      post of the latter with one of the posts of your key, and the other post
+      of this with the other pole of the switch. Now connect the motor of the
+      rotary spark gap to the power circuit and put a single-pole, single-throw
+      switch in the motor circuit, all of which is shown at <i>A</i> in <i>Fig.
+      22</i>.
+    </p>
+    <p>
+      <a name="fig022a" id="fig022a"><img width="600" height="614"
+      src="images/fig022a.jpg"
+      alt="(A) Fig. 22.--Top View of Apparatus Layout for Sending Set No. 2." /></a>
+      <a name="fig022b" id="fig022b"><img width="600" height="453"
+      src="images/fig022b.jpg"
+      alt="(B) Fig. 22.--Wiring Diagram for Sending Set No. 2." /></a>
+    </p>
+    <p>
+      Next connect the posts of the secondary coil to the posts of the rotary or
+      quenched spark gap and connect one post of the latter to one post of the
+      condenser, the other post of this to the post of the primary coil of the
+      oscillation transformer, which is the inside coil, and the clip of the
+      primary coil to the other spark gap post. This completes the closed
+      oscillation circuit. Finally connect the post of the secondary coil of the
+      oscillation transformer to the ground and the clip of it to the wire
+      leading to the aerial when you are ready to tune the set. A wiring diagram
+      of the connections is shown at <i>B</i>.
+    </p>
+    <p>
+      <i>For Direct Current.</i>--Where you have 110 volt direct current you
+      must connect in an electrolytic interrupter. This interrupter, which is
+      shown at <i>A</i> and <i>B</i> in <i>Fig. 23</i>, consists of (1) a jar
+      filled with a solution of 1 part of sulphuric acid and 9 parts of water,
+      (2) a lead electrode having a large surface fastened to the cover of
+      surface that sets in a porcelain sleeve and whose end rests on the bottom
+      of the jar.
+    </p>
+    <p>
+      <a name="fig023" id="fig023"><img width="600" height="412"
+      src="images/fig023.jpg"
+      alt="Fig. 23.--Using 110 Volt Direct Current with an Alternating Current Transformer." />
+      </a>
+    </p>
+    <p>
+      When these electrodes are connected in series with the primary of a large
+      spark coil or an alternating current transformer, see <i>C</i>, and a
+      direct current of from 40 to 110 volts is made to pass through it, the
+      current is made and broken from 1,000 to 10,000 times a minute. By raising
+      or lowering the sleeve, thus exposing more or less of the platinum, or
+      alloy point, the number of interruptions per minute can be varied at will.
+      As the electrolytic interrupter will only operate in one direction, you
+      must connect it with its platinum, or alloy anode, to the + or <i>positive</i>
+      power lead and the lead cathode to the - or <i>negative</i> power lead.
+      You can find out which is which by connecting in the interrupter and
+      trying it, or you can use a polarity indicator. An electrolytic
+      interrupter can be bought for as little as $3.00.
+    </p>
+    <p>
+      <i>How to Adjust Your Transmitter. Tuning With a Hot Wire Ammeter</i>.--A
+      transmitter can be tuned in two different ways and these are: (1) by
+      adjusting the length of the spark gap and the tuning coil so that the
+      greatest amount of energy is set up in the oscillating circuits, and (2)
+      by adjusting the apparatus so that it will send out waves of a given
+      length.
+    </p>
+    <p>
+      To adjust the transmitter so that the circuits will be in tune you should
+      have a <i>hot wire ammeter</i>, or radiation ammeter, as it is called,
+      which is shown in <i>Fig. 24</i>. It consists of a thin platinum wire
+      through which the high-frequency currents surge and these heat it; the
+      expansion and contraction of the wire moves a needle over a scale marked
+      off into fractions of an ampere. When the spark gap and tuning coil of
+      your set are properly adjusted, the needle will swing farthest to the
+      right over the scale and you will then know that the aerial wire system,
+      or open oscillation circuit, and the closed oscillation circuit are in
+      tune and radiating the greatest amount of energy.
+    </p>
+    <p>
+      <a name="fig024" id="fig024"><img width="400" height="427"
+      src="images/fig024.jpg" alt="Fig. 24.--Principle of the Hot Wire Ammeter." /></a>
+    </p>
+    <p>
+      <i>To Send Out a 200 Meter Wave Length.</i>--If you are using a condenser
+      having a capacitance of .007 microfarad, which is the largest capacity
+      value that the Government will allow an amateur to use, then if you have a
+      hot wire ammeter in your aerial and tune the inductance coil or coils
+      until the ammeter shows the largest amount of energy flowing through it
+      you will know that your transmitter is tuned and that the aerial is
+      sending out waves whose length is 200 meters. To tune to different wave
+      lengths you must have a <i>wave-meter</i>.
+    </p>
+    <p>
+      <i>The Use of the Aerial Switch.</i>--Where you intend to install both a
+      transmitter and a receptor you will need a throwover switch, or <i>aerial
+      switch</i>, as it is called. An ordinary double-pole, double-throw switch,
+      as shown at <i>A</i> in <i>Fig. 25</i>, can be used, or a switch made
+      especially for the purpose as at <i>B</i> is handier because the arc of
+      the throw is much less.
+    </p>
+    <p>
+      <a name="fig025" id="fig025"><img width="600" height="279"
+      src="images/fig025.jpg" alt="Fig. 25.--Kinds of Aerial Switches." /></a>
+    </p>
+    <p>
+      <i>Aerial Switch for a Complete Sending and Receiving Set</i>.--You can
+      buy a double-pole, double-throw switch mounted on a porcelain base for
+      about 75 cents and this will serve for <i>Set No. 1</i>. Screw this switch
+      on your table between the sending and receiving sets and then connect one
+      of the middle posts of it with the ground wire and the other middle post
+      with the lightning switch which connects with the aerial. Connect the post
+      of the tuning coil with one of the end posts of the switch and the clip of
+      the tuning coil with the other and complementary post of the switch. This
+      done, connect one of the opposite end posts of the switch to the post of
+      the receiving tuning coil and connect the sliding contact of the latter
+      with the other and complementary post of the switch as shown in <i>Fig. 26</i>.
+    </p>
+    <p>
+      <a name="fig026" id="fig026"><img width="600" height="451"
+      src="images/fig026.jpg"
+      alt="Fig. 26.--Wiring Diagram for Complete Sending and Receiving Set No. 1." />
+      </a>
+    </p>
+    <p>
+      <i>Connecting in the Lightning Switch.</i>--The aerial wire connects with
+      the middle post of the lightning switch, while one of the end posts lead
+      to one of the middle posts of the aerial switch. The other end post of the
+      lightning switch leads to a separate ground outside the building, as the
+      wiring diagrams <i>Figs. 26</i> and <i>27</i> show.
+    </p>
+    <p>
+      <a name="fig027" id="fig027"><img width="600" height="386"
+      src="images/fig027.jpg"
+      alt="Fig. 27.--Wiring Diagram for Complete Sending and Receiving Set No. 2." />
+      </a>
+    </p>
+    <h2>
+      <a name="chap05" id="chap05">CHAPTER V</a>
+    </h2>
+    <h3>
+      ELECTRICITY SIMPLY EXPLAINED
+    </h3>
+    <p>
+      It is easy to understand how electricity behaves and what it does if you
+      get the right idea of it at the start. In the first place, if you will
+      think of electricity as being a fluid like water its fundamental actions
+      will be greatly simplified. Both water and electricity may be at rest or
+      in motion. When at rest, under certain conditions, either one will develop
+      pressure, and this pressure when released will cause them to flow through
+      their respective conductors and thus produce a current.
+    </p>
+    <p>
+      <i>Electricity at Rest and in Motion</i>.--Any wire or a conductor of any
+      kind can be charged with electricity, but a Leyden jar, or other
+      condenser, is generally used to hold an electric charge because it has a
+      much larger <i>capacitance</i>, as its capacity is called, than a wire. As
+      a simple analogue of a condenser, suppose you have a tank of water raised
+      above a second tank and that these are connected together by means of a
+      pipe with a valve in it, as shown at <i>A</i> in <i>Fig. 28</i>.
+    </p>
+    <p>
+      <a name="fig028" id="fig028"><img width="594" height="320"
+      src="images/fig028.jpg"
+      alt="Fig. 28.--Water Analogue for Electric Pressure." /></a>
+    </p>
+    <table cellspacing="20" summary="Illustration">
+      <tr>
+        <td align="center">
+          <i>Photograph unavailable</i>
+        </td>
+      </tr>
+      <tr>
+        <td align="center">
+          original &copy; Underwood and Underwood.<br /> First Wireless College
+          in the World, at Tufts College, Mass.
+        </td>
+      </tr>
+    </table>
+    <p>
+      Now if you fill the upper tank with water and the valve is turned off, no
+      water can flow into the lower tank but there is a difference of pressure
+      between them, and the moment you turn the valve on a current of water will
+      flow through the pipe. In very much the same way when you have a condenser
+      charged with electricity the latter will be under <i>pressure,</i> that
+      is, a <i>difference of potential</i> will be set up, for one of the sheets
+      of metal will be charged positively and the other one, which is insulated
+      from it, will be charged negatively, as shown at <i>B</i>. On closing the
+      switch the opposite charges rush together and form a current which flows
+      to and fro between the metal plates. [Footnote: Strictly speaking it is
+      the difference of potential that sets up the electromotive force.]
+    </p>
+    <p>
+      <i>The Electric Current and Its Circuit</i>.--Just as water flowing
+      through a pipe has <i>quantity</i> and <i>pressure</i> back of it and the
+      pipe offers friction to it which tends to hold back the water, so,
+      likewise, does electricity flowing in a circuit have: (1) <i>quantity</i>,
+      or <i>current strength</i>, or just <i>current</i>, as it is called for
+      short, or <i>amperage</i>, and (2) <i>pressure</i>, or <i>potential
+      difference</i>, or <i>electromotive force</i>, or <i>voltage</i>, as it is
+      variously called, and the wire, or circuit, in which the current is
+      flowing has (3) <i>resistance</i> which tends to hold back the current.
+    </p>
+    <p>
+      A definite relation exists between the current and its electromotive force
+      and also between the current, electromotive force and the resistance of
+      the circuit; and if you will get this relationship clearly in your mind
+      you will have a very good insight into how direct and alternating currents
+      act. To keep a quantity of water flowing in a loop of pipe, which we will
+      call the circuit, pressure must be applied to it and this may be done by a
+      rotary pump as shown at <i>A in Fig. 29;</i> in the same way, to keep a
+      quantity of electricity flowing in a loop of wire, or circuit, a battery,
+      or other means for generating electric pressure must be used, as shown at
+      <i>B</i>.
+    </p>
+    <p>
+      <a name="fig029" id="fig029"><img width="600" height="291"
+      src="images/fig029.jpg"
+      alt="Fig. 29.--Water Analogues for Direct and Alternating Currents." /></a>
+    </p>
+    <p>
+      If you have a closed pipe connected with a piston pump, as at <i>C</i>, as
+      the piston moves to and fro the water in the pipe will move first one way
+      and then the other. So also when an alternating current generator is
+      connected to a wire circuit, as at <i>D</i>, the current will flow first
+      in one direction and then in the other, and this is what is called an <i>alternating
+      current</i>.
+    </p>
+    <p>
+      <i>Current and the Ampere</i>.--The amount of water flowing in a closed
+      pipe is the same at all parts of it and this is also true of an electric
+      current, in that there is exactly the same quantity of electricity at one
+      point of the circuit as there is at any other.
+    </p>
+    <p>
+      The amount of electricity, or current, flowing in a circuit in a second is
+      measured by a unit called the <i>ampere</i>, [Footnote: For definition of
+      <i>ampere</i> see <a href="#appendix">Appendix.</a>] and it is expressed
+      by the symbol I. [Footnote: This is because the letter <i>C</i> is used
+      for the symbol of <i>capacitance</i>] Just to give you an idea of the
+      quantity of current an <i>ampere</i> is we will say that a dry cell when
+      fresh gives a current of about 20 amperes. To measure the current in
+      amperes an instrument called an <i>ammeter</i> is used, as shown at <i>A</i>
+      in <i>Fig. 30</i>, and this is always connected in <i>series</i> with the
+      line, as shown at <i>B</i>.
+    </p>
+    <p>
+      <a name="fig030" id="fig030"><img width="600" height="547"
+      src="images/fig030.jpg"
+      alt="Fig. 30.--How the Ammeter and Voltmeter are Used." /></a>
+    </p>
+    <p>
+      <i>Electromotive Force and the Volt</i>.--When you have a pipe filled with
+      water or a circuit charged with electricity and you want to make them flow
+      you must use a pump in the first case and a battery or a dynamo in the
+      second case. It is the battery or dynamo that sets up the electric
+      pressure as the circuit itself is always charged with electricity.
+    </p>
+    <p>
+      The more cells you connect together in <i>series</i> the greater will be
+      the electric pressure developed and the more current it will move along
+      just as the amount of water flowing in a pipe can be increased by
+      increasing the pressure of the pump. The unit of electromotive force is
+      the <i>volt</i>, and this is the electric pressure which will force a
+      current of <i>1 ampere</i> through a resistance of <i>1 ohm</i>; it is
+      expressed by the symbol <i>E</i>. A fresh dry cell will deliver a current
+      of about 1.5 volts. To measure the pressure of a current in volts an
+      instrument called a <i>voltmeter</i> is used, as shown at <i>C</i> in <i>Fig.
+      30</i>, and this is always connected across the circuit, as shown at <i>D</i>.
+    </p>
+    <p>
+      <i>Resistance and the Ohm.</i>--Just as a water pipe offers a certain
+      amount of resistance to the flow of water through it, so a circuit opposes
+      the flow of electricity in it and this is called <i>resistance</i>.
+      Further, in the same way that a small pipe will not allow a large amount
+      of water to flow through it, so, too, a thin wire limits the flow of the
+      current in it.
+    </p>
+    <p>
+      If you connect a <i>resistance coil</i> in a circuit it acts in the same
+      way as partly closing the valve in a pipe, as shown at <i>A</i> and <i>B</i>
+      in <i>Fig. 31</i>. The resistance of a circuit is measured by a unit
+      called the <i>ohm</i>, and it is expressed by the symbol <i>R</i>. A No.
+      10, Brown and Sharpe gauge soft copper wire, 1,000 feet long, has a
+      resistance of about 1 ohm. To measure the resistance of a circuit an
+      apparatus called a <i>resistance bridge is used</i>. The resistance of a
+      circuit can, however, be easily calculated, as the following shows.
+    </p>
+    <p>
+      <a name="fig031" id="fig031"><img width="600" height="370"
+      src="images/fig031.jpg"
+      alt="Fig. 31.--Water Valve Analogue of Electric Resistance. A- a valve limits the flow of water. B- a resistance limits the flow of current." />
+      </a>
+    </p>
+    <p>
+      <i>What Ohm's Law Is</i>.--If, now, (1) you know what the current flowing
+      in a circuit is in <i>amperes</i>, and the electromotive force, or
+      pressure, is in <i>volts</i>, you can then easily find what the resistance
+      is in <i>ohms</i> of the circuit in which the current is flowing by this
+      formula:
+    </p>
+<pre xml:space="preserve">
+     Volts                   E
+    --------- = Ohms,  or   --- = R
+     Amperes                 I
+</pre>
+    <p>
+      That is, if you divide the current in amperes by the electromotive force
+      in volts the quotient will give you the resistance in ohms.
+    </p>
+    <p>
+      Or (2) if you know what the electromotive force of the current is in <i>volts</i>
+      and the resistance of the circuit is in <i>ohms</i> then you can find what
+      the current flowing in the circuit is in <i>amperes</i>, thus:
+    </p>
+<pre xml:space="preserve">
+    Volts                   E
+    ----- = Amperes,  or   --- = I
+    Ohms                    R
+</pre>
+    <p>
+      That is, by dividing the resistance of the circuit in ohms, by the
+      electromotive force of the current you will get the amperes flowing in the
+      circuit.
+    </p>
+    <p>
+      Finally (3) if you know what the resistance of the circuit is in <i>ohms</i>
+      and the current is in <i>amperes</i> then you can find what the
+      electromotive force is in <i>volts</i> since:
+    </p>
+<pre xml:space="preserve">
+    Ohms x Amperes = Volts,  or   R x I = E
+</pre>
+    <p>
+      That is, if you multiply the resistance of the circuit in ohms by the
+      current in amperes the result will give you the electromotive force in
+      volts.
+    </p>
+    <p>
+      From this you will see that if you know the value of any two of the
+      constants you can find the value of the unknown constant by a simple
+      arithmetical process. This relation between these three constants is known
+      as <i>Ohm's Law</i> and as they are very important you should memorize
+      them.
+    </p>
+    <p>
+      <i>What the Watt and Kilowatt Are.</i>--Just as <i>horsepower</i> or <i>H.P.</i>,
+      is the unit of work that steam has done or can do, so the <i>watt</i> is
+      the unit of work that an electric current has done or can do. To find the
+      <i>watts</i> a current develops you need only to multiply the <i>amperes</i>
+      by the <i>volts</i>. There are <i>746 watts</i> to <i>1 horsepower, and
+      1,000 watts are equal to 1 kilowatt</i>.
+    </p>
+    <p>
+      <i>Electromagnetic Induction.</i>--To show that a current of electricity
+      sets up a magnetic field around it you have only to hold a compass over a
+      wire whose ends are connected with a battery when the needle will swing at
+      right angles to the length of the wire. By winding an insulated wire into
+      a coil and connecting the ends of the latter with a battery you will find,
+      if you test it with a compass, that the coil is magnetic.
+    </p>
+    <p>
+      This is due to the fact that the energy of an electric current flowing in
+      the wire is partly changed into magnetic lines of force which rotate at
+      right angles about it as shown at <i>A</i> in <i>Fig. 32</i>. The magnetic
+      field produced by the current flowing in the coil is precisely the same as
+      that set up by a permanent steel magnet. Conversely, when a magnetic line
+      of force is set up a part of its energy goes to make up electric currents
+      which whirl about in a like manner, as shown at <i>B</i>.
+    </p>
+    <p>
+      <a name="fig032ab" id="fig032ab"><img width="600" height="429"
+      src="images/fig032ab.jpg"
+      alt="(A) and (B) Fig. 32.--How an Electric Current is Changed into Magnetic Lines of Force and These into an Electric Current." />
+      </a> <a name="fig032cd" id="fig032cd"><img width="600" height="504"
+      src="images/fig032cd.jpg"
+      alt="(C) and (D) Fig. 32.--How an Electric Current Sets up a Magnetic Field." />
+      </a>
+    </p>
+    <p>
+      <i>Self-induction or Inductance</i>.--When a current is made to flow in a
+      coil of wire the magnetic lines of force produced are concentrated, as at
+      C, just as a lens concentrates rays of light, and this forms an intense <i>magnetic
+      field</i>, as it is called. Now if a bar of soft iron is brought close to
+      one end of the coil of wire, or, better still, if it is pushed into the
+      coil, it will be magnetized by <i>electromagnetic induction,</i> see <i>D,</i>
+      and it will remain a magnet until the current is cut off.
+    </p>
+    <p>
+      <i>Mutual Induction</i>.--When two loops of wire, or better, two coils of
+      wire, are placed close together the electromagnetic induction between them
+      is reactive, that is, when a current is made to flow through one of the
+      coils closed magnetic lines of force are set up and when these cut the
+      other loop or turns of wire of the other coil, they in turn produce
+      electric currents in it.
+    </p>
+    <p>
+      It is the mutual induction that takes place between two coils of wire
+      which makes it possible to transform <i>low voltage currents</i> from a
+      battery or a 110 volt source of current into high pressure currents, or <i>high
+      potential currents</i>, as they are called, by means of a spark coil or a
+      transformer, as well as to <i>step up</i> and <i>step down</i> the
+      potential of the high frequency currents that are set up in sending and
+      receiving oscillation transformers. Soft iron cores are not used in
+      oscillation inductance coils and oscillation transformers for the reason
+      that the frequency of the current is so high the iron would not have time
+      to magnetize and demagnetize and so would not help along the mutual
+      induction to any appreciable extent.
+    </p>
+    <p>
+      <i>High-Frequency Currents</i>.--High frequency currents, or electric
+      oscillations as they are called, are currents of electricity that surge to
+      and fro in a circuit a million times, more or less, per second. Currents
+      of such high frequencies will <i>oscillate</i>, that is, surge to and fro,
+      in an <i>open circuit</i>, such as an aerial wire system, as well as in a
+      <i>closed circuit</i>.
+    </p>
+    <p>
+      Now there is only one method by which currents of high frequency, or <i>radio-frequency</i>,
+      as they are termed, can be set up by spark transmitters, and this is by
+      discharging a charged condenser through a circuit having a small
+      resistance. To charge a condenser a spark coil or a transformer is used
+      and the ends of the secondary coil, which delivers the high potential
+      alternating current, are connected with the condenser. To discharge the
+      condenser automatically a <i>spark,</i> or an <i>arc,</i> or the <i>flow
+      of electrons</i> in a vacuum tube, is employed.
+    </p>
+    <p>
+      <i>Constants of an Oscillation Circuit.</i>--An oscillation circuit, as
+      pointed out before, is one in which high frequency currents surge or
+      oscillate. Now the number of times a high frequency current will surge
+      forth and back in a circuit depends upon three factors of the latter and
+      these are called the constants of the circuit, namely: (1) its <i>capacitance,</i>
+      (2) its <i>inductance</i> and (3) its <i>resistance.</i>
+    </p>
+    <p>
+      <i>What Capacitance Is</i>.--The word <i>capacitance</i> means the <i>electrostatic
+      capacity</i> of a condenser or a circuit. The capacitance of a condenser
+      or a circuit is the quantity of electricity which will raise its pressure,
+      or potential, to a given amount. The capacitance of a condenser or a
+      circuit depends on its size and form and the voltage of the current that
+      is charging it.
+    </p>
+    <p>
+      The capacitance of a condenser or a circuit is directly proportional to
+      the quantity of electricity that will keep the charge at a given
+      potential. The <i>farad,</i> whose symbol is<i>M,</i> is the unit of
+      capacitance and a condenser or a circuit to have a capacitance of one
+      farad must be of such size that one <i>coulomb,</i> which is the unit of
+      electrical quantity, will raise its charge to a potential of one volt.
+      Since the farad is far too large for practical purposes a millionth of a
+      farad, or <i>microfarad</i>, whose symbol is <i>mfd.</i>, is used.
+    </p>
+    <p>
+      <i>What Inductance Is.</i>--Under the sub-caption of <i>Self-induction</i>
+      and <i>Inductance</i> in the beginning of this chapter it was shown that
+      it was the inductance of a coil that makes a current flowing through it
+      produce a strong magnetic field, and here, as one of the constants of an
+      oscillation circuit, it makes a high-frequency current act as though it
+      possessed <i>inertia</i>.
+    </p>
+    <p>
+      Inertia is that property of a material body that requires time and energy
+      to set in motion, or stop. Inductance is that property of an oscillation
+      circuit that makes an electric current take time to start and time to
+      stop. Because of the inductance, when a current flows through a circuit it
+      causes the electric energy to be absorbed and changes a large part of it
+      into magnetic lines of force. Where high frequency currents surge in a
+      circuit the inductance of it becomes a powerful factor. The practical unit
+      of inductance is the <i>henry</i> and it is represented by the symbol <i>L</i>.
+    </p>
+    <p>
+      <i>What Resistance Is.</i>--The resistance of a circuit to high-frequency
+      currents is different from that for low voltage direct or alternating
+      currents, as the former do not sink into the conductor to nearly so great
+      an extent; in fact, they stick practically to the surface of it, and hence
+      their flow is opposed to a very much greater extent. The resistance of a
+      circuit to high frequency currents is generally found in the spark gap,
+      arc gap, or the space between the electrodes of a vacuum tube. The unit of
+      resistance is, as stated, the <i>ohm</i>, and its symbol is <i>R</i>.
+    </p>
+    <p>
+      <i>The Effect of Capacitance, Inductance and Resistance on Electric
+      Oscillations</i>.--If an oscillation circuit in which high frequency
+      currents surge has a large resistance, it will so oppose the flow of the
+      currents that they will be damped out and reach zero gradually, as shown
+      at <i>A</i> in <i>Fig. 33</i>. But if the resistance of the circuit is
+      small, and in wireless circuits it is usually so small as to be
+      negligible, the currents will oscillate, until their energy is damped out
+      by radiation and other losses, as shown at <i>B</i>.
+    </p>
+    <p>
+      <a name="fig033" id="fig033"><img width="600" height="370"
+      src="images/fig033.jpg"
+      alt="Fig. 33.--The Effect of Resistance on the Discharge of an Electric Current." />
+      </a>
+    </p>
+    <p>
+      As the capacitance and the inductance of the circuit, which may be made of
+      any value, that is amount, you wish, determines the <i>time period</i>,
+      that is, the length of time for a current to make one complete
+      oscillation, it must be clear that by varying the values of the condenser
+      and the inductance coil you can make the high frequency current oscillate
+      as fast or as slow as you wish within certain limits. Where the electric
+      oscillations that are set up are very fast, the waves sent out by the
+      aerial will be short, and, conversely, where the oscillations are slow the
+      waves emitted will be long.
+    </p>
+    <h2>
+      <a name="chap06" id="chap06">CHAPTER VI</a>
+    </h2>
+    <h3>
+      HOW THE TRANSMITTING AND RECEIVING SETS WORK
+    </h3>
+    <p>
+      The easiest way to get a clear conception of how a wireless transmitter
+      sends out electric waves and how a wireless receptor receives them is to
+      take each one separately and follow: (1) in the case of the transmitter,
+      the transformation of the low voltage direct, or alternating current into
+      high potential alternating currents; then find out how these charge the
+      condenser, how this is discharged by the spark gap and sets up
+      high-frequency currents in the oscillation circuits; then (2) in the case
+      of the receptor, to follow the high frequency currents that are set up in
+      the aerial wire and learn how they are transformed into oscillations of
+      lower potential when they have a larger current strength, how these are
+      converted into intermittent direct currents by the detector and which then
+      flow into and operate the telephone receiver.
+    </p>
+    <p>
+      <i>How Transmitting Set No. 1 Works. The Battery and Spark Coil Circuit</i>.--When
+      you press down on the knob of the key the silver points of it make contact
+      and this closes the circuit; the low voltage direct current from the
+      battery now flows through the primary coil of the spark coil and this
+      magnetizes the soft iron core. The instant it becomes magnetic it pulls
+      the spring of the vibrator over to it and this breaks the circuit; when
+      this takes place the current stops flowing through the primary coil; this
+      causes the core to lose its magnetism when the vibrator spring flies back
+      and again makes contact with the adjusting screw; then the cycle of
+      operations is repeated.
+    </p>
+    <p>
+      A condenser is connected across the contact points of the vibrator since
+      this gives a much higher voltage at the ends of the secondary coil than
+      where the coil is used without it; this is because: (1) the self-induction
+      of the primary coil makes the pressure of the current rise and when the
+      contact points close the circuit again it discharges through the primary
+      coil, and (2) when the break takes place the current flows into the
+      condenser instead of arcing across the contact points.
+    </p>
+    <p>
+      <i>Changing the Primary Spark Coil Current Into Secondary Currents</i>.--Now
+      every time the vibrator contact points close the primary circuit the
+      electric current in the primary coil is changed into closed magnetic lines
+      of force and as these cut through the secondary coil they set up in it a
+      <i>momentary current</i> in one direction. Then the instant the vibrator
+      points break apart the primary circuit is opened and the closed magnetic
+      lines of force contract and as they do so they cut the turns of wire in
+      the secondary coil in the opposite direction and this sets up another
+      momentary current in the secondary coil in the other direction. The result
+      is that the low voltage direct current of the battery is changed into
+      alternating currents whose frequency is precisely that of the spring
+      vibrator, but while the frequency of the currents is low their potential,
+      or voltage, is enormously increased.
+    </p>
+    <p>
+      <i>What Ratio of Transformation Means.</i>--To make a spark coil step up
+      the low voltage direct current into high potential alternating current the
+      primary coil is wound with a couple of layers of thick insulated copper
+      wire and the secondary is wound with a thousand, more or less, number of
+      turns with very fine insulated copper wire. If the primary and secondary
+      coils were wound with the same number of turns of wire then the pressure,
+      or voltage, of the secondary coil at its terminals would be the same as
+      that of the current which flowed through the primary coil. Under these
+      conditions the <i>ratio of transformation</i>, as it is called, would be
+      unity.
+    </p>
+    <p>
+      The ratio of transformation is directly proportional to the number of
+      turns of wire on the primary and secondary coils and, since this is the
+      case, if you wind 10 turns of wire on the primary coil and 1,000 turns of
+      wire on the secondary coil then you will get 100 times as high a pressure,
+      or voltage, at the terminals of the secondary as that which you caused to
+      flow through the primary coil, but, naturally, the current strength, or
+      amperage, will be proportionately decreased.
+    </p>
+    <p>
+      <i>The Secondary Spark Coil Circuit.</i>--This includes the secondary coil
+      and the spark gap which are connected together. When the alternating, but
+      high potential, currents which are developed by the secondary coil, reach
+      the balls, or <i>electrodes</i>, of the spark gap the latter are
+      alternately charged positively and negatively.
+    </p>
+    <p>
+      Now take a given instant when one electrode is charged positively and the
+      other one is charged negatively, then when they are charged to a high
+      enough potential the electric strain breaks down the air gap between them
+      and the two charges rush together as described in the chapter before this
+      one in connection with the discharge of a condenser. When the charges rush
+      together they form a current which burns out the air in the gap and this
+      gives rise to the spark, and as the heated gap between the two electrodes
+      is a very good conductor the electric current surges forth and back with
+      high frequency, perhaps a dozen times, before the air replaces that which
+      has burned out. It is the inrushing air to fill the vacuum of the gap that
+      makes the crackling noise which accompanies the discharge of the electric
+      spark.
+    </p>
+    <p>
+      In this way then electric oscillations of the order of a million, more or
+      less, are produced and if an aerial and a ground wire are connected to the
+      spark balls, or electrodes, the oscillations will surge up and down it and
+      the energy of these in turn, are changed into electric waves which travel
+      out into space. An open circuit transmitter of this kind will send out
+      waves that are four times as long as the aerial itself, but as the waves
+      it sends out are strongly damped the Government will not permit it to be
+      used.
+    </p>
+    <p>
+      <i>The Closed Oscillation Circuit.</i>--By using a closed oscillation
+      circuit the transmitter can be tuned to send out waves of a given length
+      and while the waves are not so strongly damped more current can be sent
+      into the aerial wire system. The closed oscillation circuit consists of:
+      (1) a <i>spark gap</i>, (2) a <i>condenser</i> and (3) an <i>oscillation
+      transformer</i>. The high potential alternating current delivered by the
+      secondary coil not only charges the spark gap electrodes which necessarily
+      have a very small capacitance, but it charges the condenser which has a
+      large capacitance and the value of which can be changed at will.
+    </p>
+    <p>
+      Now when the condenser is fully charged it discharges through the spark
+      gap and then the electric oscillations set up surge to and fro through the
+      closed circuit. As a closed circuit is a very poor radiator of energy,
+      that is, the electric oscillations are not freely converted into electric
+      waves by it, they surge up to, and through the aerial wire; now as the
+      aerial wire is a good radiator nearly all of the energy of the electric
+      oscillations which surge through it are converted into electric waves.
+    </p>
+    <p>
+      <i>How Transmitting Set No. 2 Works. With Alternating Current.</i> The
+      operation of a transmitting set that uses an alternating current
+      transformer, or <i>power transformer,</i> as it is sometimes called, is
+      even more simple than one using a spark coil. The transformer needs no
+      vibrator when used with alternating current. The current from a generator
+      flows through the primary coil of the transformer and the alternations of
+      the usual lighting current is 60 cycles per second. This current sets up
+      an alternating magnetic field in the core of the transformer and as these
+      magnetic lines of force expand and contract they set up alternating
+      currents of the same frequency but of much higher voltage at the terminals
+      of the secondary coil according to the ratio of the primary and secondary
+      turns of wire as explained under the sub-caption of <i>Ratio of
+      Transformation</i>.
+    </p>
+    <p>
+      <i>With Direct Current</i>.--When a 110 volt direct current is used to
+      energize the power transformer an <i>electrolytic</i> interruptor is
+      needed to make and break the primary circuit, just as a vibrator is needed
+      for the same purpose with a spark coil. When the electrodes are connected
+      in series with the primary coil of a transformer and a source of direct
+      current having a potential of 40 to 110 volts, bubbles of gas are formed
+      on the end of the platinum, or alloy anode, which prevent the current from
+      flowing until the bubbles break and then the current flows again, in this
+      way the current is rapidly made and broken and the break is very sharp.
+    </p>
+    <p>
+      Where this type of interrupter is employed the condenser that is usually
+      shunted around the break is not necessary as the interrupter itself has a
+      certain inherent capacitance, due to electrolytic action, and which is
+      called its <i>electrolytic capacitance</i>, and this is large enough to
+      balance the self-induction of the circuit since the greater the number of
+      breaks per minute the smaller the capacitance required.
+    </p>
+    <p>
+      <i>The Rotary Spark Gap</i>.--In this type of spark gap the two fixed
+      electrodes are connected with the terminals of the secondary coil of the
+      power transformer and also with the condenser and primary of the
+      oscillation transformer. Now whenever any pair of electrodes on the
+      rotating disk are in a line with the pair of fixed electrodes a spark will
+      take place, hence the pitch of the note depends on the speed of the motor
+      driving the disk. This kind of a rotary spark-gap is called <i>non-synchronous</i>
+      and it is generally used where a 60 cycle alternating current is available
+      but it will work with other higher frequencies.
+    </p>
+    <p>
+      <i>The Quenched Spark Gap</i>.--If you strike a piano string a single
+      quick blow it will continue to vibrate according to its natural period.
+      This is very much the way in which a quenched spark gap sets up
+      oscillations in a coupled closed and open circuit. The oscillations set up
+      in the primary circuit by a quenched spark make only three or four sharp
+      swings and in so doing transfer all of their energy over to the secondary
+      circuit, where it will oscillate some fifty times or more before it is
+      damped out, because the high frequency currents are not forced, but simply
+      oscillate to the natural frequency of the circuit. For this reason the
+      radiated waves approach somewhat the condition of continuous waves, and so
+      sharper tuning is possible.
+    </p>
+    <p>
+      <i>The Oscillation Transformer.</i>--In this set the condenser in the
+      closed circuit is charged and discharged and sets up oscillations that
+      surge through the closed circuit as in <i>Set No. 1</i>. In this set,
+      however, an oscillation transformer is used and as the primary coil of it
+      is included in the closed circuit the oscillations set up in it produce
+      strong oscillating magnetic lines of force. The magnetic field thus
+      produced sets up in turn electric oscillations in the secondary coil of
+      the oscillation transformer and these surge through the aerial wire system
+      where their energy is radiated in the form of electric waves.
+    </p>
+    <p>
+      The great advantage of using an oscillation transformer instead of a
+      simple inductance coil is that the capacitance of the closed circuit can
+      be very much larger than that of the aerial wire system. This permits more
+      energy to be stored up by the condenser and this is impressed on the
+      aerial when it is radiated as electric waves.
+    </p>
+    <p>
+      <i>How Receiving Set No. I Works.</i>--When the electric waves from a
+      distant sending station impinge on the wire of a receiving aerial their
+      energy is changed into electric oscillations that are of exactly the same
+      frequency (assuming the receptor is tuned to the transmitter) but whose
+      current strength (amperage) and potential (voltage) are very small. These
+      electric waves surge through the closed circuit but when they reach the
+      crystal detector the contact of the metal point on the crystal permits
+      more current to flow through it in one direction than it will allow to
+      pass in the other direction. For this reason a crystal detector is
+      sometimes called a <i>rectifier</i>, which it really is.
+    </p>
+    <p>
+      Thus the high frequency currents which the steel magnet cores of the
+      telephone receiver would choke off are changed by the detector into
+      intermittent direct currents which can flow through the magnet coils of
+      the telephone receiver. Since the telephone receiver chokes off the
+      oscillations, a small condenser can be shunted around it so that a
+      complete closed oscillation circuit is formed and this gives better
+      results.
+    </p>
+    <p>
+      When the intermittent rectified current flows through the coils of the
+      telephone receiver it energizes the magnet as long as it lasts, when it is
+      de-energized; this causes the soft iron disk, or <i>diaphragm</i> as it is
+      called, which sets close to the ends of the poles of the magnet, to
+      vibrate; and this in turn gives forth sounds such as dots and dashes,
+      speech or music, according to the nature of the electric waves that sent
+      them out at the distant station.
+    </p>
+    <p>
+      <i>How Receiving Set No. 2 Works.</i>--When the electric oscillations that
+      are set up by the incoming electric waves on the aerial wire surge through
+      the primary coil of the oscillation transformer they produce a magnetic
+      field and as the lines of force of the latter cut the secondary coil,
+      oscillations of the same frequency are set up in it. The potential
+      (voltage) of these oscillations are, however, <i>stepped down</i> in the
+      secondary coil and, hence, their current strength (amperes) is increased.
+    </p>
+    <p>
+      The oscillations then flow through the closed circuit where they are
+      rectified by the crystal detector and transformed into sound waves by the
+      telephone receiver as described in connection with <i>Set No. 1</i>. The
+      variable condenser shunted across the closed circuit permits finer
+      secondary tuning to be done than is possible without it. Where you are
+      receiving continuous waves from a wireless telephone transmitter (speech
+      or music) you have to tune sharper than is possible with the tuning coil
+      alone and to do this a variable condenser connected in parallel with the
+      secondary coil is necessary.
+    </p>
+    <h2>
+      <a name="chap07" id="chap07">CHAPTER VII</a>
+    </h2>
+    <h3>
+      MECHANICAL AND ELECTRICAL TUNING
+    </h3>
+    <p>
+      There is a strikingly close resemblance between <i>sound waves</i> and the
+      way they are set up in <i>the air</i> by a mechanically vibrating body,
+      such as a steel spring or a tuning fork, and <i>electric waves</i> and the
+      way they are set up in <i>the ether</i> by a current oscillating in a
+      circuit. As it is easy to grasp the way that sound waves are produced and
+      behave something will be told about them in this chapter and also an
+      explanation of how electric waves are produced and behave and thus you
+      will be able to get a clear understanding of them and of tuning in
+      general.
+    </p>
+    <p>
+      <i>Damped and Sustained Mechanical Vibrations</i>.--If you will place one
+      end of a flat steel spring in a vice and screw it up tight as shown at <i>A</i>
+      in <i>Fig. 34</i>, and then pull the free end over and let it go it will
+      vibrate to and fro with decreasing amplitude until it comes to rest as
+      shown at <i>B</i>. When you pull the spring over you store up energy in it
+      and when you let it go the stored up energy is changed into energy of
+      motion and the spring moves forth and back, or <i>vibrates</i> as we call
+      it, until all of its stored up energy is spent.
+    </p>
+    <p>
+      <a name="fig034" id="fig034"><img width="600" height="474"
+      src="images/fig034.jpg"
+      alt="Fig. 34.--Damped and Sustained Mechanical Vibrations." /></a>
+    </p>
+    <p>
+      If it were not for the air surrounding it and other frictional losses, the
+      spring would vibrate for a very long time as the stored up energy and the
+      energy of motion would practically offset each other and so the energy
+      would not be used up. But as the spring beats the air the latter is sent
+      out in impulses and the conversion of the vibrations of the spring into
+      waves in the air soon uses up the energy you have imparted to it and it
+      comes to rest.
+    </p>
+    <p>
+      In order to send out <i>continuous waves</i> in the air instead of <i>damped
+      waves</i> as with a flat steel spring you can use an <i>electric driven
+      tuning fork</i>, see <i>C</i>, in which an electromagnet is fixed on the
+      inside of the prongs and when this is energized by a battery current the
+      vibrations of the prongs of the fork are kept going, or are <i>sustained</i>,
+      as shown in the diagram at <i>D</i>.
+    </p>
+    <p>
+      <i>Damped and Sustained Electric Oscillations</i>.--The vibrating steel
+      spring described above is a very good analogue of the way that damped
+      electric oscillations which surge in a circuit set up and send out
+      periodic electric waves in the ether while the electric driven tuning fork
+      just described is likewise a good analogue of how sustained oscillations
+      surge in a circuit and set up and send out continuous electric waves in
+      the ether as the following shows.
+    </p>
+    <p>
+      Now the inductance and resistance of a circuit such as is shown at <i>A</i>
+      in <i>Fig. 35</i>, slows down, and finally damps out entirely, the
+      electric oscillations of the high frequency currents, see <i>B</i>, where
+      these are set up by the periodic discharge of a condenser, precisely as
+      the vibrations of the spring are damped out by the friction of the air and
+      other resistances that act upon it. As the electric oscillations surge to
+      and fro in the circuit it is opposed by the action of the ether which
+      surrounds it and electric waves are set up in and sent out through it and
+      this transformation soon uses up the energy of the current that flows in
+      the circuit.
+    </p>
+    <p>
+      <a name="fig035" id="fig035"><img width="600" height="435"
+      src="images/fig035.jpg"
+      alt="Fig. 35.--Damped and Sustained Electric Oscillations." /></a>
+    </p>
+    <p>
+      To send out <i>continuous waves</i> in the ether such as are needed for
+      wireless telephony instead of <i>damped waves</i> which are, at the
+      present writing, generally used for wireless telegraphy, an <i>electric
+      oscillation arc</i> or a <i>vacuum tube oscillator</i> must be used, see
+      <i>C</i>, instead of a spark gap. Where a spark gap is used the condenser
+      in the circuit is charged periodically and with considerable lapses of
+      time between each of the charging processes, when, of course, the
+      condenser discharges periodically and with the same time element between
+      them. Where an oscillation arc or a vacuum tube is used the condenser is
+      charged as rapidly as it is discharged and the result is the oscillations
+      are sustained as shown at <i>D</i>.
+    </p>
+    <p>
+      <i>About Mechanical Tuning</i>.--A tuning fork is better than a spring or
+      a straight steel bar for setting up mechanical vibrations. As a matter of
+      fact a tuning fork is simply a steel bar bent in the middle so that the
+      two ends are parallel. A handle is attached to middle point of the fork so
+      that it can be held easily and which also allows it to vibrate freely,
+      when the ends of the prongs alternately approach and recede from one
+      another. When the prongs vibrate the handle vibrates up and down in unison
+      with it, and imparts its motion to the <i>sounding box</i>, or <i>resonance
+      case</i> as it is sometimes called, where one is used.
+    </p>
+    <p>
+      If, now, you will mount the fork on a sounding box which is tuned so that
+      it will be in resonance with the vibrations of the fork there will be a
+      direct reinforcement of the vibrations when the note emitted by it will be
+      augmented in strength and quality. This is called <i>simple resonance</i>.
+      Further, if you mount a pair of forks, each on a separate sounding box,
+      and have the forks of the same size, tone and pitch, and the boxes
+      synchronized, that is, tuned to the same frequency of vibration, then set
+      the two boxes a foot or so apart, as shown at A in <i>Fig. 36</i>, when
+      you strike one of the forks with a rubber hammer it will vibrate with a
+      definite frequency and, hence, send out sound waves of a given length.
+      When the latter strike the second fork the impact of the molecules of air
+      of which the sound waves are formed will set its prongs to vibrating and
+      it will, in turn, emit sound waves of the same length and this is called
+      <i>sympathetic resonance</i>, or as we would say in wireless the forks are
+      <i>in tune</i>.
+    </p>
+    <p>
+      <a name="fig036" id="fig036"><img width="600" height="351"
+      src="images/fig036.jpg"
+      alt="Fig. 36.--Sound Wave and Electric Wave Tuned Senders and Receptors. A - variable tuning forks for showing sound wave tuning. B - variable oscillation circuits for showing electric wave tuning." />
+      </a>
+    </p>
+    <p>
+      Tuning forks are made with adjustable weights on their prongs and by
+      fixing these to different parts of them the frequency with which the forks
+      vibrate can be changed since the frequency varies inversely with the
+      square of the length and directly with the thickness [Footnote: This law
+      is for forks having a rectangular cross-section. Those having a round
+      cross-section vary as the radius.] of the prongs. Now by adjusting one of
+      the forks so that it vibrates at a frequency of, say, 16 per second and
+      adjusting the other fork so that it vibrates at a frequency of, say, 18 or
+      20 per second, then the forks will not be in tune with each other and,
+      hence, if you strike one of them the other will not respond. But if you
+      make the forks vibrate at the same frequency, say 16, 20 or 24 per second,
+      when you strike one of them the other will vibrate in unison with it.
+    </p>
+    <p>
+      <i>About Electric Tuning</i>.--Electric resonance and electric tuning are
+      very like those of acoustic resonance and acoustic tuning which I have
+      just described. Just as acoustic resonance may be simple or sympathetic so
+      electric resonance may be simple or sympathetic. Simple acoustic resonance
+      is the direct reinforcement of a simple vibration and this condition is
+      had when a tuning fork is mounted on a sounding box. In simple electric
+      resonance an oscillating current of a given frequency flowing in a circuit
+      having the proper inductance and capacitance may increase the voltage
+      until it is several times greater than its normal value. Tuning the
+      receptor circuits to the transmitter circuits are examples of sympathetic
+      electric resonance. As a demonstration if you have two Leyden jars
+      (capacitance) connected in circuit with two loops of wire (inductance)
+      whose inductance can be varied as shown at <i>B</i> in <i>Fig. 36,</i>
+      when you make a spark pass between the knobs of one of them by means of a
+      spark coil then a spark will pass in the gap of the other one provided the
+      inductance of the two loops of wire is the same. But if you vary the
+      inductance of the one loop so that it is larger or smaller than that of
+      the other loop no spark will take place in the second circuit.
+    </p>
+    <p>
+      When a tuning fork is made to vibrate it sends out waves in the air, or
+      sound waves, in all directions and just so when high frequency currents
+      surge in an oscillation circuit they send out waves in the ether, or
+      electric waves, that travel in all directions. For this reason electric
+      waves from a transmitting station cannot be sent to one particular
+      station, though they do go further in one direction than in another,
+      according to the way your aerial wire points.
+    </p>
+    <p>
+      Since the electric waves travel out in all directions any receiving set
+      properly tuned to the wave length of the sending station will receive the
+      waves and the only limit on your ability to receive from high-power
+      stations throughout the world depends entirely on the wave length and
+      sensitivity of your receiving set. As for tuning, just as changing the
+      length and the thickness of the prongs of a tuning fork varies the
+      frequency with which it vibrates and, hence, the length of the waves it
+      sends out, so, too, by varying the capacitance of the condenser and the
+      inductance of the tuning coil of the transmitter the frequency of the
+      electric oscillations set up in the circuit may be changed and,
+      consequently, the length of the electric waves they send out. Likewise, by
+      varying the capacitance and the inductance of the receptor the circuits
+      can be tuned to receive incoming electric waves of whatever length within
+      the limitation of the apparatus.
+    </p>
+    <h2>
+      <a name="chap08" id="chap08">CHAPTER VIII</a>
+    </h2>
+    <h3>
+      A SIMPLE VACUUM TUBE DETECTOR RECEIVING SET
+    </h3>
+    <p>
+      While you can receive dots and dashes from spark wireless telegraph
+      stations and hear spoken words and music from wireless telephone stations
+      with a crystal detector receiving set such as described in <a
+      href="#chap03">Chapter III</a>, you can get stations that are much farther
+      away and hear them better with a <i>vacuum tube detector</i> receiving
+      set.
+    </p>
+    <p>
+      Though the vacuum tube detector requires two batteries to operate it and
+      the receiving circuits are somewhat more complicated than where a crystal
+      detector is used still the former does not have to be constantly adjusted
+      as does the latter and this is another very great advantage. Taken all in
+      all the vacuum tube detector is the most sensitive and the most
+      satisfactory of the detectors that are in use at the present time.
+    </p>
+    <p>
+      Not only is the vacuum tube a detector of electric wave signals and speech
+      and music but it can also be used to <i>amplify</i> them, that is, to make
+      them stronger and, hence, louder in the telephone receiver and further its
+      powers of amplification are so great that it will reproduce them by means
+      of a <i>loud speaker</i>, just as a horn amplifies the sounds of a
+      phonograph reproducer, until they can be heard by a room or an auditorium
+      full of people. There are two general types of loud speakers, though both
+      use the principle of the telephone receiver. The construction of these
+      loud speakers will be fully described in a later chapter.
+    </p>
+    <p>
+      <i>Assembled Vacuum Tube Receiving Sets</i>.--You can buy a receiving set
+      with a vacuum tube detector from the very simplest type, which is
+      described in this chapter, to those that are provided with <i>regenerative
+      circuits</i> and <i>amplifying</i> tubes or both, which we shall describe
+      in later chapters, from dealers in electrical apparatus generally. While
+      one of these sets costs more than you can assemble a set for yourself,
+      still, especially in the beginning, it is a good plan to buy an assembled
+      one for it is fitted with a <i>panel</i> on which the adjusting knobs of
+      the rheostat, tuning coil and condenser are mounted and this makes it
+      possible to operate it as soon as you get it home and without the
+      slightest trouble on your part.
+    </p>
+    <p>
+      You can, however, buy all the various parts separately and mount them
+      yourself. If you want the receptor simply for receiving then it is a good
+      scheme to have all of the parts mounted in a box or enclosed case, but if
+      you want it for experimental purposes then the parts should be mounted on
+      a base or a panel so that all of the connections are in sight and
+      accessible.
+    </p>
+    <p>
+      <i>A Simple Vacuum Tube Receiving Set.</i>--For this set you should use:
+      (1) a <i>loose coupled tuning coil,</i> (2) a <i>variable condenser,</i>
+      (3) a <i>vacuum tube detector,</i> (4) an <i>A</i> or <i>storage battery</i>
+      giving 6 volts, (5) a <i>B</i> or <i>dry cell battery</i> giving 22-1/2
+      volts, (6) a <i>rheostat</i> for varying the storage battery current, and
+      (7) a pair of 2,000-ohm <i>head telephone receivers</i>. The loose coupled
+      tuning coil, the variable condenser and the telephone receivers are the
+      same as those described in <a href="#chap03">Chapter III</a>.
+    </p>
+    <p>
+      <i>The Vacuum Tube Detector. With Two Electrodes.</i>--A vacuum tube in
+      its simplest form consists of a glass bulb like an incandescent lamp in
+      which a <i>wire filament</i> and a <i>metal plate</i> are sealed as shown
+      in <i>Fig. 37</i>, The air is then pumped out of the tube and a vacuum
+      left or after it is exhausted it is filled with nitrogen, which cannot
+      burn.
+    </p>
+    <p>
+      <a name="fig037" id="fig037"><img width="493" height="480"
+      src="images/fig037.jpg"
+      alt="Fig. 37.--Two Electrode Vacuum Tube Detectors." /></a>
+    </p>
+    <p>
+      When the vacuum tube is used as a detector, the wire filament is heated
+      red-hot and the metal plate is charged with positive electricity though it
+      remains cold. The wire filament is formed into a loop like that of an
+      incandescent lamp and its outside ends are connected with a 6-volt storage
+      battery, which is called the <i>A</i> battery; then the + or <i>positive</i>
+      terminal of a 22-1/2 volt dry cell battery, called the <i>B</i> battery,
+      is connected to the metal plate while the - or <i>negative</i> terminal of
+      the battery is connected to one of the terminals of the wire filament. The
+      diagram, <i>Fig. 37</i>, simply shows how the two electrode vacuum tube,
+      the <i>A</i> or dry battery, and the <i>B</i> or storage battery are
+      connected up.
+    </p>
+    <p>
+      <i>Three Electrode Vacuum Tube Detector.</i>--The three electrode vacuum
+      tube detector shown at <i>A</i> in <i>Fig. 38</i>, is much more sensitive
+      than the two electrode tube and has, in consequence, all but supplanted
+      it. In this more recent type of vacuum tube the third electrode, or <i>grid</i>,
+      as it is called, is placed between the wire filament and the metal plate
+      and this allows the current to be increased or decreased at will to a very
+      considerable extent.
+    </p>
+    <p>
+      <a name="fig038" id="fig038"><img width="600" height="531"
+      src="images/fig038.jpg"
+      alt="Fig. 38.--Three Electrode Vacuum Tube Detector and Battery Connections." />
+      </a>
+    </p>
+    <p>
+      The way the three electrode vacuum tube detector is connected with the
+      batteries is shown at <i>B</i>. The plate, the <i>A</i> or dry cell
+      battery and one terminal of the filament are connected in <i>series</i>--that
+      is, one after the other, and the ends of the filament are connected to the
+      <i>B</i> or storage battery. In assembling a receiving set you must, of
+      course, have a socket for the vacuum tube. A vacuum tube detector costs
+      from $5.00 to $6.00.
+    </p>
+    <p>
+      <i>The Dry Cell and Storage Batteries</i>.--The reason that a storage
+      battery is used for heating the filament of the vacuum tube detector is
+      because the current delivered is constant, whereas when a dry cell battery
+      is used the current soon falls off and, hence, the heat of the filament
+      gradually grows less. The smallest <i>A</i> or 6 volt storage battery on
+      the market has a capacity of 20 to 40 ampere hours, weighs 13 pounds and
+      costs about $10.00. It is shown at <i>A</i> in <i>Fig. 39</i>. The <i>B</i>
+      or dry cell battery for the vacuum tube plate circuit that gives 22-1/2
+      volts can be bought already assembled in sealed boxes. The small size is
+      fitted with a pair of terminals while the larger size is provided with <i>taps</i>
+      so that the voltage required by the plate can be adjusted as the proper
+      operation of the tube requires careful regulation of the plate voltage. A
+      dry cell battery for a plate circuit is shown at <i>B</i>.
+    </p>
+    <p>
+      <a name="fig039" id="fig039"><img width="600" height="336"
+      src="images/fig039.jpg"
+      alt="Fig. 39.--&lt;i&gt;A&lt;/i&gt; and &lt;i&gt;B&lt;/i&gt; Batteries for Vacuum Tube Detectors." />
+      </a>
+    </p>
+    <p>
+      <i>The Filament Rheostat</i>.--An adjustable resistance, called a <i>rheostat</i>,
+      must be used in the filament and storage battery circuit so that the
+      current flowing through the filament can be controlled to a nicety. The
+      rheostat consists of an insulating and a heat resisting form on which is
+      wound a number of turns of resistance wire. A movable contact arm that
+      slides over and presses on the turns of wire is fixed to the knob on top
+      of the rheostat. A rheostat that has a resistance of 6 ohms and a current
+      carrying capacity of 1.5 amperes which can be mounted on a panel board is
+      the right kind to use. It is shown at <i>A</i> and <i>B</i> in <i>Fig. 40</i>
+      and costs $1.25.
+    </p>
+    <p>
+      <a name="fig040" id="fig040"><img width="600" height="411"
+      src="images/fig040.jpg"
+      alt="Fig. 40.--Rheostat for the &lt;i&gt;A&lt;/i&gt; or Storage Battery Current." />
+      </a>
+    </p>
+    <p>
+      <i>Assembling the Parts</i>.--Begin by placing all of the separate parts
+      of the receiving set on a board or a base of other material and set the
+      tuning coil on the left hand side with the adjustable switch end toward
+      the right hand side so that you can reach it easily. Then set the variable
+      condenser in front of it, set the vacuum tube detector at the right hand
+      end of the tuning coil and the rheostat in front of the detector. Place
+      the two sets of batteries back of the instruments and screw a couple of
+      binding posts <i>a</i> and <i>b</i> to the right hand lower edge of the
+      base for connecting in the head phones all of which is shown at <i>A</i>
+      in <i>Fig. 41</i>.
+    </p>
+    <p>
+      <a name="fig041a" id="fig041a"><img width="600" height="473"
+      src="images/fig041a.jpg"
+      alt="(A) Fig. 41.--Top View of Apparatus Layout for a Vacuum Tube Detector Receiving Set." />
+      </a> <a name="fig041b" id="fig041b"><img width="600" height="482"
+      src="images/fig041b.jpg"
+      alt="(B) Fig. 41.--Wiring Diagram of a Simple Vacuum Tube Receiving Set." />
+      </a>
+    </p>
+    <p>
+      <i>Connecting Up the Parts.</i>--To wire up the different parts begin by
+      connecting the sliding contact of the primary coil of the loose coupled
+      tuning coil (this you will remember is the outside one that is wound with
+      fine wire) to the upper post of the lightning switch and connect one
+      terminal of this coil with the water pipe. Now connect the free end of the
+      secondary coil of the tuning coil (this is the inside coil that is wound
+      with heavy wire) to one of the binding posts of the variable condenser and
+      connect the movable contact arm of the adjustable switch of the primary of
+      the tuning coil with the other post of the variable condenser.
+    </p>
+    <p>
+      Next connect the grid of the vacuum tube to one of the posts of the
+      condenser and then connect the plate of the tube to the <i>carbon terminal</i>
+      of the <i>B</i> or dry cell battery which is the + or <i>positive pole</i>
+      and connect the <i>zinc terminal</i> of the - or <i>negative</i> pole to
+      the binding post <i>a</i>, connect the post <i>b</i> to the other side of
+      the variable condenser and then connect the terminals of the head phones
+      to the binding posts <i>a</i> and <i>b</i>. Whatever you do be careful not
+      to get the plate connections of the battery reversed.
+    </p>
+    <p>
+      Now connect one of the posts of the rheostat to one terminal of the
+      filament and the other terminal of the filament to the - or <i>negative</i>
+      terminal of the <i>A</i> or storage battery and the + or <i>positive</i>
+      terminal of the <i>A</i> or storage battery to the other post of the
+      rheostat. Finally connect the + or positive terminal of the <i>A</i> or
+      storage battery with the wire that runs from the head phones to the
+      variable condenser, all of which is shown in the wiring diagram at <i>B</i>
+      in <i>Fig. 41</i>.
+    </p>
+    <p>
+      <i>Adjusting the Vacuum Tube Detector Receiving Set</i>.--A vacuum tube
+      detector is tuned exactly in the same way as the <i>Crystal Detector Set
+      No. 2</i> described in <a href="#chap03">Chapter III</a>, in-so-far as the
+      tuning coil and variable condenser are concerned. The sensitivity of the
+      vacuum tube detector receiving set and, hence, the distance over which
+      signals and other sounds can be heard depends very largely on the
+      sensitivity of the vacuum tube itself and this in turn depends on: (1) the
+      right amount of heat developed by the filament, or <i>filament brilliancy</i>
+      as it is called, (2) the right amount of voltage applied to the plate, and
+      (3) the extent to which the tube is exhausted where this kind of a tube is
+      used.
+    </p>
+    <p>
+      To vary the current flowing from the <i>A</i> or storage battery through
+      the filament so that it will be heated to the right degree you adjust the
+      rheostat while you are listening in to the signals or other sounds. By
+      carefully adjusting the rheostat you can easily find the point at which it
+      makes the tube the most sensitive. A rheostat is also useful in that it
+      keeps the filament from burning out when the current from the battery
+      first flows through it. You can very often increase the sensitiveness of a
+      vacuum tube after you have used it for a while by recharging the <i>A</i>
+      or storage battery.
+    </p>
+    <p>
+      The degree to which a vacuum tube has been exhausted has a very pronounced
+      effect on its sensitivity. The longer the tube is used the lower its
+      vacuum gets and generally the less sensitive it becomes. When this takes
+      place (and you can only guess at it) you can very often make it more
+      sensitive by warming it over the flame of a candle. Vacuum tubes having a
+      gas content (in which case they are, of course, no longer vacuum tubes in
+      the strict sense) make better detectors than tubes from which the air has
+      been exhausted and which are sealed off in this evacuated condition
+      because their sensitiveness is not dependent on the degree of vacuum as in
+      the latter tubes. Moreover, a tube that is completely exhausted costs more
+      than one that is filled with gas.
+    </p>
+    <h2>
+      <a name="chap09" id="chap09">CHAPTER IX</a>
+    </h2>
+    <h3>
+      VACUUM TUBE AMPLIFIER RECEIVING SETS
+    </h3>
+    <p>
+      The reason a vacuum tube detector is more sensitive than a crystal
+      detector is because while the latter merely <i>rectifies</i> the
+      oscillating current that surges in the receiving circuits, the former acts
+      as an <i>amplifier</i> at the same time. The vacuum tube can be used as a
+      separate amplifier in connection with either: (1) a <i>crystal detector</i>
+      or (2) a <i>vacuum tube detector</i>, and (<i>a</i>) it will amplify
+      either the <i>radio frequency currents</i>, that is the high frequency
+      oscillating currents which are set up in the oscillation circuits or (<i>b</i>)
+      it will amplify the <i>audio frequency currents</i>, that is, the <i>low
+      frequency alternating</i> currents that flow through the head phone
+      circuit.
+    </p>
+    <p>
+      To use the amplified radio frequency oscillating currents or amplified
+      audio frequency alternating currents that are set up by an amplifier tube
+      either a high resistance, called a <i>grid leak</i>, or an <i>amplifying
+      transformer</i>, with or without an iron core, must be connected with the
+      plate circuit of the first amplifier tube and the grid circuit of the next
+      amplifier tube or detector tube, or with the wire point of a crystal
+      detector. Where two or more amplifier tubes are coupled together in this
+      way the scheme is known as <i>cascade amplification.</i>
+    </p>
+    <p>
+      Where either a <i>radio frequency transformer</i>, that is one without the
+      iron core, or an <i>audio frequency transformer</i>, that is one with the
+      iron core, is used to couple the amplifier tube circuits together better
+      results are obtained than where a high resistance grid leak is used, but
+      the amplifying tubes have to be more carefully shielded from each other or
+      they will react and set up a <i>howling</i> noise in the head phones. On
+      the other hand grid leaks cost less but they are more troublesome to use
+      as you have to find out for yourself the exact resistance value they must
+      have and this you can do only by testing them out.
+    </p>
+    <p>
+      <i>A Grid Leak Amplifier Receiving Set. With Crystal Detector.</i>--The
+      apparatus you need for this set includes: (1) a <i>loose coupled tuning
+      coil</i>, (2) a <i>variable condenser</i>, (3) <i>two fixed condensers</i>,
+      (4) a <i>crystal detector</i>, or better a <i>vacuum tube detector</i>,
+      (5) an <i>A</i> or <i>6 volt storage battery</i>, (6) a <i>rheostat</i>,
+      (7) a <i>B</i> or 22-1/2 <i>volt dry cell battery</i>, (8) a fixed
+      resistance unit, or <i>leak grid</i> as it is called, and (9) a pair of <i>head-phones</i>.
+      The tuning coil, variable condenser, fixed condensers, crystal detectors
+      and head-phones are exactly the same as those described in <i>Set No. 2</i>
+      in <a href="#chap03">Chapter III</a>. The <i>A</i> and <i>B batteries</i>
+      are exactly the same as those described in <a href="#chap08">Chapter VIII</a>.
+      The <i>vacuum tube amplifier</i> and the <i>grid leak</i> are the only new
+      pieces of apparatus you need and not described before.
+    </p>
+    <p>
+      <i>The Vacuum Tube Amplifier</i>.--This consists of a three electrode
+      vacuum tube exactly like the vacuum tube detector described in <a
+      href="#chap08">Chapter VIII</a> and pictured in <i>Fig. 38</i>, except
+      that instead of being filled with a non-combustible gas it is evacuated,
+      that is, the air has been completely pumped out of it. The gas filled
+      tube, however, can be used as an amplifier and either kind of tube can be
+      used for either radio frequency or audio frequency amplification, though
+      with the exhausted tube it is easier to obtain the right plate and
+      filament voltages for good working.
+    </p>
+    <p>
+      <i>The Fixed Resistance Unit, or Grid Leak</i>.--Grid leaks are made in
+      different ways but all of them have an enormously high resistance. One way
+      of making them consists of depositing a thin film of gold on a sheet of
+      mica and placing another sheet of mica on top to protect it the whole
+      being enclosed in a glass tube as shown at <i>A</i> in <i>Fig. 42</i>.
+      These grid leaks are made in units of from 50,000 ohms (.05 megohm) to
+      5,000,000 ohms (5 megohms) and cost from $1 to $2.
+    </p>
+    <p>
+      <a name="fig042" id="fig042"><img width="600" height="531"
+      src="images/fig042.jpg"
+      alt="Fig. 42.--Grid Leaks and How to Connect Them up." /></a>
+    </p>
+    <p>
+      As the <i>value</i> of the grid leak you will need depends very largely
+      upon the construction of the different parts of your receiving set and on
+      the kind of aerial wire system you use with it you will have to try out
+      various resistances until you hit the right one. The resistance that will
+      give the best results, however, lies somewhere between 500,000 ohms (1/2 a
+      megohm) and 3,000,000 ohms (3 megohms) and the only way for you to find
+      this out is to buy 1/2, 1 and 2 megohm grid leak resistances and connect
+      them up in different ways, as shown at <i>B</i>, until you find the right
+      value.
+    </p>
+    <p>
+      <i>Assembling the Parts for a Crystal Detector Set</i>.--Begin by laying
+      the various parts out on a base or a panel with the loose coupled tuning
+      coil on the left hand side, but with the adjustable switch of the
+      secondary coil on the right hand end or in front according to the way it
+      is made. Then place the variable condenser, the rheostat, the crystal
+      detector and the binding posts for the head phones in front of and in a
+      line with each other. Set the vacuum tube amplifier back of the rheostat
+      and the <i>A</i> and <i>B</i> batteries back of the parts or in any other
+      place that may be convenient. The fixed condensers and the grid leak can
+      be placed anywhere so that it will be easy to connect them in and you are
+      ready to wire up the set.
+    </p>
+    <p>
+      <i>Connecting Up the Parts for a Crystal Detector</i>.--First connect the
+      sliding contact of the primary of the tuning coil to the leading-in wire
+      and one of the end wires of the primary to the water pipe, as shown in <i>Fig.
+      43</i>. Now connect the adjustable arm that makes contact with one end of
+      the secondary of the tuning coil to one of the posts of the variable
+      condenser; then connect the other post of the latter with a post of the
+      fixed condenser and the other post of this with the grid of the amplifying
+      tube.
+    </p>
+    <p>
+      <a name="fig043" id="fig043"><img width="600" height="404"
+      src="images/fig043.jpg"
+      alt="Fig. 43.--Crystal Detector Receiving Set with Vacuum Tube Amplifier (Resistance Coupled)." />
+      </a>
+    </p>
+    <p>
+      Connect the first post of the variable condenser to the + or <i>positive
+      electrode</i> of the <i>A</i> battery and its - or <i>negative electrode</i>
+      with the rotating contact arm of the rheostat. Next connect one end of the
+      resistance coil of the rheostat to one of the posts of the amplifier tube
+      that leads to the filament and the other filament post to the + or <i>positive
+      electrode</i> of the <i>A</i> battery. This done connect the <i>negative</i>,
+      that is, the <i>zinc pole</i> of the <i>B</i> battery to the positive
+      electrode of the <i>A</i> battery and connect the <i>positive</i>, or <i>carbon
+      pole</i> of the former with one end of the grid leak and connect the other
+      end of this to the plate of the amplifier tube.
+    </p>
+    <p>
+      To the end of the grid leak connected with the plate of the amplifier tube
+      connect the metal point of your crystal detector, the crystal of the
+      latter with one post of the head phones and the other post of them with
+      the other end of the grid leak and, finally, connect a fixed condenser in
+      <i>parallel</i> with--that is across the ends of the grid leak, all of
+      which is shown in the wiring diagram in <i>Fig. 43</i>.
+    </p>
+    <p>
+      <i>A Grid Leak Amplifying Receiving Set With Vacuum Tube Detector</i>.--A
+      better amplifying receiving set can be made than the one just described by
+      using a vacuum tube detector instead of the crystal detector. This set is
+      built up exactly like the crystal detector described above and shown in <i>Fig.
+      43</i> up to and including the grid leak resistance, but shunted across
+      the latter is a vacuum tube detector, which is made and wired up precisely
+      like the one shown at <i>A</i> in <i>Fig. 41</i> in the chapter ahead of
+      this one. The way a grid leak and vacuum tube detector with a one-step
+      amplifier are connected up is shown at <i>A</i> in <i>Fig. 44</i>. Where
+      you have a vacuum tube detector and one or more amplifying tubes connected
+      up, or in <i>cascade</i> as it is called, you can use an <i>A</i>, or
+      storage battery of 6 volts for all of them as shown at <i>B</i> in <i>Fig.
+      44</i>, but for every vacuum tube you use you must have a <i>B</i> or
+      22-1/2 volt dry battery to charge the plate with.
+    </p>
+    <p>
+      <a name="fig044a" id="fig044a"><img width="600" height="375"
+      src="images/fig044a.jpg"
+      alt="(A) Fig. 44--Vacuum Tube Detector Set with One Step Amplifier (Resistance Coupled)." />
+      </a> <a name="fig044b" id="fig044b"><img width="582" height="320"
+      src="images/fig044b.jpg"
+      alt="(B) Fig. 44.--Wiring Diagram for Using One A or Storage Battery with an Amplifier and a Detector Tube." />
+      </a>
+    </p>
+    <p>
+      <i>A Radio Frequency Transformer Amplifying Receiving Set</i>.--Instead of
+      using a grid leak resistance to couple up the amplifier and detector tube
+      circuits you can use a <i>radio frequency transformer</i>, that is, a
+      transformer made like a loose coupled tuning coil, and without an iron
+      core, as shown in the wiring diagram at <i>A</i> in <i>Fig. 45</i>. In
+      this set, which gives better results than where a grid leak is used, the
+      amplifier tube is placed in the first oscillation circuit and the detector
+      tube in the second circuit.
+    </p>
+    <p>
+      <a name="fig045a" id="fig045a"><img width="600" height="394"
+      src="images/fig045a.jpg"
+      alt="(A) Fig. 45.--Wiring Diagram for a Radio Frequency Transformer Amplifying Receiving Set." />
+      </a> <a name="fig045b" id="fig045b"><img width="412" height="320"
+      src="images/fig045b.jpg" alt="(B) Fig. 45.--Radio Frequency Transformer." /></a>
+    </p>
+    <p>
+      Since the radio frequency transformer has no iron core the high frequency,
+      or <i>radio frequency</i> oscillating currents, as they are called, surge
+      through it and are not changed into low frequency, or <i>audio frequency</i>
+      pulsating currents, until they flow through the detector. Since the
+      diagram shows only one amplifier and one radio frequency transformer, it
+      is consequently a <i>one step amplifier</i>; however, two, three or more,
+      amplifying tubes can be connected up by means of an equal number of radio
+      frequency transformers when you will get wonderful results. Where a six
+      step amplifier, that is, where six amplifying tubes are connected
+      together, or in <i>cascade</i>, the first three are usually coupled up
+      with radio frequency transformers and the last three with audio frequency
+      transformers. A radio frequency transformer is shown at <i>B</i> and costs
+      $6 to $7.
+    </p>
+    <p>
+      <i>An Audio Frequency Transformer Amplifying Receiving Set</i>.--Where
+      audio frequency transformers are used for stepping up the voltage of the
+      current of the detector and amplifier tubes, the radio frequency current
+      does not get into the plate circuit of the detector at all for the reason
+      that the iron core of the transformer chokes them off, hence, the
+      succeeding amplifiers operate at audio frequencies. An audio frequency
+      transformer is shown at <i>A</i> in <i>Fig. 46</i> and a wiring diagram
+      showing how the tubes are connected in <i>cascade</i> with the
+      transformers is shown at <i>B</i>; it is therefore a two-step audio
+      frequency receiving set.
+    </p>
+    <p>
+      <a name="fig046a" id="fig046a"><img width="400" height="304"
+      src="images/fig046a.jpg" alt="(A) Fig. 46.--Audio Frequency Transformer." /></a>
+      <a name="fig046b" id="fig046b"><img width="600" height="331"
+      src="images/fig046b.jpg"
+      alt="(B) Fig. 46--Wiring Diagram for an Audio Frequency Transformer Amplifying Receiving Set. (With Vacuum Tube Detector and Two Step Amplifier Tubes.)" />
+      </a>
+    </p>
+    <p>
+      <i>A Six Step Amplifier Receiving Set With a Loop Aerial.</i>--By using a
+      receiving set having a three step radio frequency and a three step audio
+      frequency, that is, a set in which there are coupled three amplifying
+      tubes with radio frequency transformers and three amplifying tubes with
+      audio frequency transformers as described under the caption <i>A Radio
+      Frequency Transformer Receiving Set</i>, you can use a <i>loop aerial</i>
+      in your room thus getting around the difficulties--if such there be--in
+      erecting an out-door aerial. You can easily make a loop aerial by winding
+      10 turns of <i>No. 14</i> or <i>16</i> copper wire about 1/16 inch apart
+      on a wooden frame two feet on the side as shown in <i>Fig. 47</i>. With
+      this six step amplifier set and loop aerial you can receive wave lengths
+      of 150 to 600 meters from various high power stations which are at
+      considerable distances away.
+    </p>
+    <p>
+      <a name="fig047a" id="fig047a"><img width="600" height="346"
+      src="images/fig047a.jpg"
+      alt="(A) Fig. 47.--Six Step Amplifier with Loop Aerial." /></a> <a
+      name="fig047b" id="fig047b"><img width="600" height="453"
+      src="images/fig047b.jpg"
+      alt="(B) Fig. 47.--Efficient Regenerative Receiving Set. (With Three Coil Loose Coupler Tuner.)" />
+      </a>
+    </p>
+    <p>
+      <i>How to Prevent Howling</i>.--Where radio frequency or audio frequency
+      amplifiers are used to couple your amplifier tubes in cascade you must
+      take particular pains to shield them from one another in order to prevent
+      the <i>feed back</i> of the currents through them, which makes the head
+      phones or loud speaker <i>howl</i>. To shield them from each other the
+      tubes should be enclosed in metal boxes and placed at least 6 inches apart
+      while the transformers should be set so that their cores are at right
+      angles to each other and these also should be not less than six inches
+      apart.
+    </p>
+    <h2>
+      <a name="chap10" id="chap10">CHAPTER X</a>
+    </h2>
+    <h3>
+      REGENERATIVE AMPLIFICATION RECEIVING SETS
+    </h3>
+    <p>
+      While a vacuum tube detector has an amplifying action of its own, and this
+      accounts for its great sensitiveness, its amplifying action can be further
+      increased to an enormous extent by making the radio frequency currents
+      that are set up in the oscillation circuits react on the detector.
+    </p>
+    <p>
+      Such currents are called <i>feed-back</i> or <i>regenerative</i> currents
+      and when circuits are so arranged as to cause the currents to flow back
+      through the detector tube the amplification keeps on increasing until the
+      capacity of the tube itself is reached. It is like using steam over and
+      over again in a steam turbine until there is no more energy left in it. A
+      system of circuits which will cause this regenerative action to take place
+      is known as the <i>Armstrong circuits</i> and is so called after the young
+      man who discovered it.
+    </p>
+    <p>
+      Since the regenerative action of the radio frequency currents is produced
+      by the detector tube itself and which sets up an amplifying effect without
+      the addition of an amplifying tube, this type of receiving set has found
+      great favor with amateurs, while in combination with amplifying tubes it
+      multiplies their power proportionately and it is in consequence used in
+      one form or another in all the better sets.
+    </p>
+    <p>
+      There are many different kinds of circuits which can be used to produce
+      the regenerative amplification effect while the various kinds of tuning
+      coils will serve for coupling them; for instance a two or three slide
+      single tuning coil will answer the purpose but as it does not give good
+      results it is not advisable to spend either time or money on it. A better
+      scheme is to use a loose coupler formed of two or three honeycomb or other
+      compact coils, while a <i>variocoupler</i> or a <i>variometer</i> or two
+      will produce the maximum regenerative action.
+    </p>
+    <p>
+      <i>The Simplest Type of Regenerative Receiving Set. With Loose Coupled
+      Tuning Coil</i>.--While this regenerative set is the simplest that will
+      give anything like fair results it is here described not on account of its
+      desirability, but because it will serve to give you the fundamental idea
+      of how the <i>feed-back</i> circuit is formed.
+    </p>
+    <p>
+      For this set you need: (1) a <i>loose-coupled tuning coil</i> such as
+      described in <a href="#chap03">Chapter III</a>, (2) a <i>variable
+      condenser</i> of <i>.001 mfd.</i> (microfarad) capacitance; (3) one <i>fixed
+      condenser</i> of <i>.001 mfd.</i>; (4) one <i>fixed condenser</i> for the
+      grid leak circuit of <i>.00025 mfd.</i>; (5) a <i>grid leak</i> of 1/2 to
+      2 megohms resistance; (6) a <i>vacuum tube detector</i>; (7) an <i>A 6
+      volt battery</i>; (8) a <i>rheostat</i>; (9) a <i>B 22 1/2 volt battery</i>;
+      and (10) a pair of <i>2000 ohm head phones</i>.
+    </p>
+    <p>
+      <i>Connecting Up the Parts.</i>--Begin by connecting the leading-in wire
+      of the aerial with the binding post end of the primary coil of the loose
+      coupler as shown in the wiring diagram <i>Fig. 48</i> and then connect the
+      sliding contact with the water pipe or other ground. Connect the binding
+      post end of the primary coil with one post of the variable condenser,
+      connect the other post of this with one of the posts of the <i>.00025 mfd.</i>
+      condenser and the other end of this with the grid of the detector tube;
+      then around this condenser shunt the grid leak resistance.
+    </p>
+    <p>
+      <a name="fig048" id="fig048"><img width="600" height="510"
+      src="images/fig048.jpg"
+      alt="Fig. 48.--Simple Regenerative Receiving Set. (With Loose Coupler Tuner.)" />
+      </a>
+    </p>
+    <p>
+      Next connect the sliding contact of the primary coil with the other post
+      of the variable condenser and from this lead a wire on over to one of the
+      terminals of the filament of the vacuum tube; to the other terminal of the
+      filament connect one of the posts of the rheostat and connect the other
+      post to the - or negative electrode of the <i>A</i> battery and then
+      connect the + or positive electrode of it to the other terminal of the
+      filament.
+    </p>
+    <p>
+      Connect the + or positive electrode of the <i>A</i> battery with one post
+      of the .001 mfd. fixed condenser and connect the other post of this to one
+      of the ends of the secondary coil of the tuning coil and which is now
+      known as the <i>tickler coil</i>; then connect the other end of the
+      secondary, or tickler coil to the plate of the vacuum tube. In the wiring
+      diagram the secondary, or tickler coil is shown above and in a line with
+      the primary coil but this is only for the sake of making the connections
+      clear; in reality the secondary, or tickler coil slides to and fro in the
+      primary coil as shown and described in <a href="#chap03">Chapter III</a>.
+      Finally connect the <i>negative</i>, or zinc pole of the <i>B battery</i>
+      to one side of the fixed condenser, the <i>positive</i>, or carbon, pole
+      to one of the terminals of the head phones and the other terminal of this
+      to the other post of the fixed condenser when your regenerative set is
+      complete.
+    </p>
+    <p>
+      <i>An Efficient Regenerative Receiving Set. With Three Coil Loose Coupler.</i>--To
+      construct a really good regenerative set you must use a loose coupled
+      tuner that has three coils, namely a <i>primary</i>, a <i>secondary</i>
+      and a <i>tickler coil</i>. A tuner of this kind is made like an ordinary
+      loose coupled tuning coil but it has a <i>third</i> coil as shown at <i>A</i>
+      and <i>B</i> in <i>Fig. 49</i>. The middle coil, which is the <i>secondary</i>,
+      is fixed to the base, and the large outside coil, which is the <i>primary</i>,
+      is movable, that is it slides to and fro over the middle coil, while the
+      small inside coil, which is the <i>tickler</i>, is also movable and can
+      slide in or out of the middle <i>coil</i>. None of these coils is
+      variable; all are wound to receive waves up to 360 meters in length when
+      used with a variable condenser of <i>.001 mfd</i>. capacitance. In other
+      words you slide the coils in and out to get the right amount of coupling
+      and you tune by adjusting the variable condenser to get the exact wave
+      length you want.
+    </p>
+    <p>
+      <a name="fig049a" id="fig049a"><img width="600" height="355"
+      src="images/fig049a.jpg"
+      alt="(A) Fig. 49.--Diagram of a Three Coil Coupler." /></a> <a
+      name="fig049b" id="fig049b"><img width="553" height="240"
+      src="images/fig049b.jpg"
+      alt="(B) Fig. 49.--Three Coil Loose Coupler Tuner." /></a>
+    </p>
+    <p>
+      <i>With Compact Coils</i>.--Compact coil tuners are formed of three fixed
+      inductances wound in flat coils, and these are pivoted in a mounting so
+      that the distance between them and, therefore, the coupling, can be
+      varied, as shown at <i>A</i> in <i>Fig. 50</i>. These coils are wound up
+      by the makers for various wave lengths ranging from a small one that will
+      receive waves of any length up to 360 meters to a large one that has a
+      maximum of 24,000 meters. For an amateur set get three of the smallest
+      coils when you can not only hear amateur stations that send on a 200 meter
+      wave but broadcasting stations that send on a 360 meter wave.
+    </p>
+    <p>
+      <a name="fig050" id="fig050"><img width="599" height="320"
+      src="images/fig050.jpg" alt="Fig. 50.--Honeycomb Inductance Coil." /></a>
+    </p>
+    <p>
+      These three coils are mounted with panel plugs which latter fit into a
+      stand, or mounting, so that the middle coil is fixed, that is, stationary,
+      while the two outside coils can be swung to and fro like a door; this
+      scheme permits small variations of coupling to be had between the coils
+      and this can be done either by handles or by means of knobs on a panel
+      board. While I have suggested the use of the smallest size coils, you can
+      get and use those wound for any wave length you want to receive and when
+      those are connected with variometers and variable condensers, and with a
+      proper aerial, you will have a highly efficient receptor that will work
+      over all ranges of wave lengths. The smallest size coils cost about $1.50
+      apiece and the mounting costs about $6 or $7 each.
+    </p>
+    <p>
+      <i>The A Battery Potentiometer</i>.--This device is simply a resistance
+      like the rheostat described in connection with the preceding vacuum tube
+      receiving sets but it is wound to 200 or 300 ohms resistance as against
+      1-1/2 to 6 ohms of the rheostat. It is, however, used as well as the
+      rheostat. With a vacuum tube detector, and especially with one having a
+      gas-content, a potentiometer is very necessary as it is only by means of
+      it that the potential of the plate of the detector can be accurately
+      regulated. The result of proper regulation is that when the critical
+      potential value is reached there is a marked increase in the loudness of
+      the sounds that are emitted by the head phones.
+    </p>
+    <p>
+      As you will see from <i>A</i> in <i>Fig. 51</i> it has three taps. The two
+      taps which are connected with the ends of the resistance coil are shunted
+      around the <i>A</i> battery and the third tap, which is attached to the
+      movable contact arm, is connected with the <i>B</i> battery tap, see <i>B</i>,
+      at which this battery gives 18 volts. Since the <i>A</i> battery gives 6
+      volts you can vary the potential of the plate from 18 to 24 volts. The
+      potentiometer must never be shunted around the <i>B</i> battery or the
+      latter will soon run down. A potentiometer costs a couple of dollars.
+    </p>
+    <p>
+      <a name="fig051a" id="fig051a"><img width="600" height="392"
+      src="images/fig051a.jpg" alt="(A) Fig. 51.--The Use of the Potentiometer." /></a>
+    </p>
+    <p>
+      <i>The Parts and How to Connect Them Up.</i>--For this regenerative set
+      you will need: (1) a <i>honeycomb</i> or other compact <i>three-coil tuner</i>,
+      (2) two <i>variable</i> (<i>.001</i> and <i>.0005 mfd</i>.) <i>condensers</i>;
+      (3) a <i>.00025 mfd. fixed condenser</i>; (4) a <i>1/2 to 2 megohm grid
+      leak</i>; (5) a <i>tube detector</i>; (6) a <i>6 volt A battery</i>; (7)
+      <i>a rheostat</i>; (8) a <i>potentiometer</i>; (9) an <i>18</i> or <i>20
+      volt B battery</i>; (10) a <i>fixed condenser</i> of <i>.001 mfd. fixed
+      condenser</i>; and (11) a <i>pair of 2000 ohm head phones</i>.
+    </p>
+    <p>
+      To wire up the parts connect the leading-in wire of the aerial with the
+      primary coil, which is the middle one of the tuner, and connect the other
+      terminal with the ground. Connect the ends of the secondary coil, which is
+      the middle one, with the posts of the variable condenser and connect one
+      of the posts of the latter with one post of the fixed .00025 mfd.
+      condenser and the other post of this with the grid; then shunt the grid
+      leak around it. Next connect the other post of the variable condenser to
+      the - or <i>negative</i> electrode of the <i>A battery</i>; the + or <i>positive</i>
+      electrode of this to one terminal of the detector filament and the other
+      end of the latter to the electrode of the <i>A</i> battery.
+    </p>
+    <p>
+      Now connect one end of the tickler coil with the detector plate and the
+      other post to the fixed .001 mfd. condenser, then the other end of this to
+      the positive or carbon pole of the <i>B</i> battery.
+    </p>
+    <p>
+      This done shunt the potentiometer around the <i>A</i> battery and run a
+      wire from the movable contact of it (the potentiometer) over to the 18
+      volt tap, (see <i>B</i>, <i>Fig. 51</i>), of the <i>B</i> battery.
+      Finally, shunt the head phones and the .001 mfd. fixed condenser and you
+      are ready to try out conclusions.
+    </p>
+    <p>
+      <i>A Regenerative Audio Frequency Amplifier Receiving Set.</i>--The use of
+      amateur regenerative cascade audio frequency receiving sets is getting to
+      be quite common. To get the greatest amplification possible with
+      amplifying tubes you have to keep a negative potential on the grids. You
+      can, however, get very good results without any special charging
+      arrangement by simply connecting one post of the rheostat with the
+      negative terminal of the filament and connecting the <i>low potential</i>
+      end of the secondary of the tuning coil with the - or negative electrode
+      of the <i>A</i> battery. This scheme will give the grids a negative bias
+      of about 1 volt. You do not need to bother about these added factors that
+      make for high efficiency until after you have got your receiving set in
+      working order and understand all about it.
+    </p>
+    <p>
+      <i>The Parts and How to Connect Them Up.</i>--Exactly the same parts are
+      needed for this set as the one described above, but in addition you will
+      want: (1) two more <i>rheostats</i>; (2) <i>two</i> more sets of <i>B</i>
+      22-1/2 <i>volt batteries</i>; (3) <i>two amplifier tubes</i>, and (4) <i>two
+      audio frequency transformers</i> as described in <a href="#chap09">Chapter
+      IX</a> and pictured at <i>A</i> in <i>Fig. 46</i>.
+    </p>
+    <p>
+      To wire up the parts begin by connecting the leading-in wire to one end of
+      the primary of the tuning coil and then connect the other end of the coil
+      with the ground. A variable condenser of .001 mfd. capacitance can be
+      connected in the ground wire, as shown in <i>Fig. 52</i>, to good
+      advantage although it is not absolutely needed. Now connect one end of the
+      secondary coil to one post of a <i>.001 mfd.</i> variable condenser and
+      the other end of the secondary to the other post of the condenser.
+    </p>
+    <p>
+      <a name="fig052" id="fig052"><img width="600" height="348"
+      src="images/fig052.jpg"
+      alt="Fig. 52.--Regenerative Audio Frequency Amplifier Receiving Set." /></a>
+    </p>
+    <p>
+      Next bring a lead (wire) from the first post of the variable condenser
+      over to the post of the first fixed condenser and connect the other post
+      of the latter with the grid of the detector tube. Shunt 1/2 to 2 megohm
+      grid leak resistance around the fixed condenser and then connect the
+      second post of the variable condenser to one terminal of the detector tube
+      filament. Run this wire on over and connect it with the first post of the
+      second rheostat, the second post of which is connected with one terminal
+      of the filament of the first amplifying tube; then connect the first post
+      of the rheostat with one end of the secondary coil of the first audio
+      frequency transformer, and the other end of this coil with the grid of the
+      first amplifier tube.
+    </p>
+    <p>
+      Connect the lead that runs from the second post of variable condenser to
+      the first post of the third rheostat, the second post of which is
+      connected with one terminal of the second amplifying tube; then connect
+      the first post of the rheostat with one end of the secondary coil of the
+      second audio frequency transformer and the other end of this coil with the
+      grid of the second amplifier tube.
+    </p>
+    <p>
+      This done connect the - or negative electrode of the <i>A</i> battery with
+      the second post of the variable condenser and connect the + or positive
+      electrode with the free post of the first rheostat, the other post of
+      which connects with the free terminal of the filament of the detector.
+      From this lead tap off a wire and connect it to the free terminal of the
+      filament of the first amplifier tube, and finally connect the end of the
+      lead with the free terminal of the filament of the second amplifier tube.
+    </p>
+    <p>
+      Next shunt a potentiometer around the <i>A</i> battery and connect the
+      third post, which connects with the sliding contact, to the negative or
+      zinc pole of a <i>B</i> battery, then connect the positive or carbon pole
+      of it to the negative or zinc pole of a second <i>B</i> battery and the
+      positive or carbon pole of the latter with one end of the primary coil of
+      the second audio frequency transformer and the other end of it to the
+      plate of the first amplifying tube. Run the lead on over and connect it to
+      one of the terminals of the second fixed condenser and the other terminal
+      of this with the plate of the second amplifying tube. Then shunt the
+      headphones around the condenser.
+    </p>
+    <p>
+      Finally connect one end of the tickler coil of the tuner with the plate of
+      the detector tube and connect the other end of the tickler to one end of
+      the primary coil of the first audio frequency transformer and the other
+      end of it to the wire that connects the two <i>B</i> batteries together.
+    </p>
+    <h2>
+      <a name="chap11" id="chap11">CHAPTER XI</a>
+    </h2>
+    <h3>
+      SHORT WAVE REGENERATIVE RECEIVING SETS
+    </h3>
+    <p>
+      A <i>short wave receiving set</i> is one that will receive a range of wave
+      lengths of from 150 to 600 meters while the distance over which the waves
+      can be received as well as the intensity of the sounds reproduced by the
+      headphones depends on: (1) whether it is a regenerative set and (2)
+      whether it is provided with amplifying tubes.
+    </p>
+    <p>
+      High-grade regenerative sets designed especially for receiving amateur
+      sending stations that must use a short wave length are built on the
+      regenerative principle just like those described in the last chapter and
+      further amplification can be had by the use of amplifier tubes as
+      explained in <a href="#chap09">Chapter IX</a>, but the new feature of
+      these sets is the use of the <i>variocoupler</i> and one or more <i>variometers</i>.
+      These tuning devices can be connected up in different ways and are very
+      popular with amateurs at the present time.
+    </p>
+    <p>
+      Differing from the ordinary loose coupler the variometer has no movable
+      contacts while the variometer is provided with taps so that you can
+      connect it up for the wave length you want to receive. All you have to do
+      is to tune the oscillation circuits to each other is to turn the <i>rotor</i>,
+      which is the secondary coil, around in the <i>stator</i>, as the primary
+      coil is called in order to get a very fine variation of the wave length.
+      It is this construction that makes <i>sharp tuning</i> with these sets
+      possible, by which is meant that all wave lengths are tuned out except the
+      one which the receiving set is tuned for.
+    </p>
+    <p>
+      <i>A Short Wave Regenerative Receiver--With One Variometer and Three
+      Variable Condensers.</i>--This set also includes a variocoupler and a <i>grid
+      coil</i>. The way that the parts are connected together makes it a simple
+      and at the same time a very efficient regenerative receiver for short
+      waves. While this set can be used without shielding the parts from each
+      other the best results are had when shields are used.
+    </p>
+    <p>
+      The parts you need for this set include: (1) one <i>variocoupler</i>; (2)
+      one <i>.001 microfarad variable condenser</i>; (3) one <i>.0005 microfarad
+      variable condenser</i>; (4) one <i>.0007 microfarad variable condenser</i>;
+      (5) <i>one 2 megohm grid leak</i>; (6) one <i>vacuum tube detector</i>;
+      (7) one <i>6 volt A battery</i>; (8) one <i>6 ohm</i>, 1-1/2 <i>ampere
+      rheostat</i>; (9) one <i>200 ohm potentiometer</i>; (10) one 22-1/2 <i>volt
+      B battery</i>; (11) one <i>.001 microfarad fixed condenser</i>, (12) one
+      pair of <i>2,000 ohm headphones</i>, and (13) a <i>variometer</i>.
+    </p>
+    <p>
+      <i>The Variocoupler</i>.--A variocoupler consists of a primary coil wound
+      on the outside of a tube of insulating material and to certain turns of
+      this taps are connected so that you can fix the wave length which your
+      aerial system is to receive from the shortest wave; <i>i.e.</i>, 150
+      meters on up by steps to the longest wave, <i>i.e.</i>, 600 meters, which
+      is the range of most amateur variocouplers that are sold in the open
+      market. This is the part of the variocoupler that is called the <i>stator</i>.
+    </p>
+    <p>
+      The secondary coil is wound on the section of a ball mounted on a shaft
+      and this is swung in bearings on the stator so that it can turn in it.
+      This part of the variocoupler is called the <i>rotor</i> and is arranged
+      so that it can be mounted on a panel and adjusted by means of a knob or a
+      dial. A diagram of a variocoupler is shown at <i>A</i> in <i>Fig. 53</i>,
+      and the coupler itself at <i>B</i>. There are various makes and
+      modifications of variocouplers on the market but all of them are about the
+      same price which is $6.00 or $8.00.
+    </p>
+    <p>
+      <a name="fig053" id="fig053"><img width="600" height="461"
+      src="images/fig053.jpg"
+      alt="Fig. 53.--How the Variocoupler is Made and Works." /></a>
+    </p>
+    <p>
+      <i>The Variometer.</i>--This device is quite like the variocoupler, but
+      with these differences: (1) the rotor turns in the stator, which is also
+      the section of a ball, and (2) one end of the primary is connected with
+      one end of the secondary coil. To be really efficient a variometer must
+      have a small resistance and a large inductance as well as a small
+      dielectric loss. To secure the first two of these factors the wire should
+      be formed of a number of fine, pure copper wires each of which is
+      insulated and the whole strand then covered with silk. This kind of wire
+      is the best that has yet been devised for the purpose and is sold under
+      the trade name of <i>litzendraht</i>.
+    </p>
+    <p>
+      A new type of variometer has what is known as a <i>basket weave</i>, or <i>wavy
+      wound</i> stator and rotor. There is no wood, insulating compound or other
+      dielectric materials in large enough quantities to absorb the weak
+      currents that flow between them, hence weaker sounds can be heard when
+      this kind of a variometer is used. With it you can tune sharply to waves
+      under 200 meters in length and up to and including wave lengths of 360
+      meters. When amateur stations of small power are sending on these short
+      waves this style of variometer keeps the electric oscillations at their
+      greatest strength and, hence, the reproduced sounds will be of maximum
+      intensity. A wiring diagram of a variometer is shown at <i>A</i> in <i>Fig.
+      54</i> and a <i>basketball</i> variometer is shown complete at <i>B</i>.
+    </p>
+    <p>
+      <a name="fig054" id="fig054"><img width="600" height="329"
+      src="images/fig054.jpg"
+      alt="Fig. 54.--How the Variometer is Made and Works." /></a>
+    </p>
+    <p>
+      <i>Connecting Up the Parts</i>.--To hook-up the set connect the leading-in
+      wire to one end of the primary coil, or stator, of the variocoupler and
+      solder a wire to one of the taps that gives the longest wave length you
+      want to receive. Connect the other end of this wire with one post of a
+      .001 microfarad variable condenser and connect the other post with the
+      ground as shown in <i>Fig. 55</i>. Now connect one end of the secondary
+      coil, or rotor, to one post of a .0007 mfd. variable condenser, the other
+      post of this to one end of the grid coil and the other end of this with
+      the remaining end of the rotor of the variocoupler.
+    </p>
+    <p>
+      <a name="fig055" id="fig055"><img width="600" height="386"
+      src="images/fig055.jpg"
+      alt="Fig. 55.--Short Wave Regenerative Receiving Set (one Variometer and three Variable Condensers.)" />
+      </a>
+    </p>
+    <p>
+      Next connect one post of the .0007 mfd. condenser with one of the
+      terminals of the detector filament; then connect the other post of this
+      condenser with one post of the .0005 mfd. variable condenser and the other
+      post of this with the grid of the detector, then shunt the megohm grid
+      leak around the latter condenser. This done connect the other terminal of
+      the filament to one post of the rheostat, the other post of this to the -
+      or negative electrode of the 6 volt <i>A</i> battery and the + or positive
+      electrode of the latter to the other terminal of the filament.
+    </p>
+    <p>
+      Shunt the potentiometer around the <i>A</i> battery and connect the
+      sliding contact with the - or zinc pole of the <i>B</i> battery and the +
+      or carbon pole with one terminal of the headphone; connect the other
+      terminal to one of the posts of the variometer and the other post of the
+      variometer to the plate of the detector. Finally shunt a .001 mfd. fixed
+      condenser around the headphones. If you want to amplify the current with a
+      vacuum tube amplifier connect in the terminals of the amplifier circuit
+      shown at <i>A</i> in <i>Figs. 44</i> or <i>45</i> at the point where they
+      are connected with the secondary coil of the loose coupled tuning coil, in
+      those diagrams with the binding posts of <i>Fig. 55</i> where the phones
+      are usually connected in.
+    </p>
+    <p>
+      <i>Short Wave Regenerative Receiver. With Two Variometers and Two Variable
+      Condensers.</i>--This type of regenerative receptor is very popular with
+      amateurs who are using high-grade short-wave sets. When you connect up
+      this receptor you must keep the various parts well separated. Screw the
+      variocoupler to the middle of the base board or panel, and secure the
+      variometers on either side of it so that the distance between them will be
+      9 or 10 inches. By so placing them the coupling will be the same on both
+      sides and besides you can shield them from each other easier.
+    </p>
+    <p>
+      For the shield use a sheet of copper on the back of the panel and place a
+      sheet of copper between the parts, or better, enclose the variometers and
+      detector and amplifying tubes if you use the latter in sheet copper boxes.
+      When you set up the variometers place them so that their stators are at
+      right angles to each other for otherwise the magnetic lines of force set
+      up by the coils of each one will be mutually inductive and this will make
+      the headphones or loud speaker <i>howl</i>. Whatever tendency the receptor
+      has to howl with this arrangement can be overcome by putting in a grid
+      leak of the right resistance and adjusting the condenser.
+    </p>
+    <p>
+      <i>The Parts and How to Connect Them Up.</i>--For this set you require:
+      (1) one <i>variocoupler</i>; (2) two <i>variometers</i>; (3) one <i>.001
+      microfarad variable condenser</i>; (4) one <i>.0005 microfarad variable
+      condenser</i>; (5) one <i>2 megohm grid leak resistance</i>; (6) one <i>vacuum
+      tube detector</i>; (7) one <i>6 volt A battery</i>; (8) one <i>200 ohm
+      potentiometer</i>; (9) one <i>22-1/2 volt B battery</i>; (10) one <i>.001
+      microfarad fixed condenser</i>, and (11) one pair of <i>2,000 ohm
+      headphones</i>.
+    </p>
+    <p>
+      To wire up the set begin by connecting the leading-in wire to the fixed
+      end of the primary coil, or <i>stator</i>, of the variocoupler, as shown
+      in <i>Fig. 56</i>, and connect one post of the .001 mfd. variable
+      condenser to the stator by soldering a short length of wire to the tap of
+      the latter that gives the longest wave you want to receive. Now connect
+      one end of the secondary coil, or <i>rotor</i>, of the variocoupler with
+      one post of the .0005 mfd. variable condenser and the other part to the
+      grid of the detector tube. Connect the other end of the rotor of the
+      variocoupler to one of the posts of the first variometer and the other
+      post of this to one of the terminals of the detector filament.
+    </p>
+    <p>
+      <a name="fig056" id="fig056"><img width="600" height="349"
+      src="images/fig056.jpg"
+      alt="Fig. 56.--Short Wave Regenerative Receiving Set (two Variometers and two Variable Condensers.)" />
+      </a>
+    </p>
+    <p>
+      Connect this filament terminal with the - or negative electrode of the <i>A</i>
+      battery and the + or positive electrode of this with one post of the
+      rheostat and lead a wire from the other post to the free terminal of the
+      filament. This done shunt the potential around the <i>A</i> battery and
+      connect the sliding contact to the - or zinc pole of the <i>B</i> battery
+      and the + or carbon pole of this to one terminal of the headphones, while
+      the other terminal of this leads to one of the posts of the second
+      variometer, the other post of which is connected to the plate of the
+      detector tube. If you want to add an amplifier tube then connect it to the
+      posts instead of the headphones as described in the foregoing set.
+    </p>
+    <h2>
+      <a name="chap12" id="chap12">CHAPTER XII</a>
+    </h2>
+    <h3>
+      INTERMEDIATE AND LONG WAVE REGENERATIVE RECEIVING SETS
+    </h3>
+    <p>
+      All receiving sets that receive over a range of wave lengths of from 150
+      meters to 3,000 meters are called <i>intermediate wave sets</i> and all
+      sets that receive wave lengths over a range of anything more than 3,000
+      meters are called <i>long wave sets</i>. The range of intermediate wave
+      receptors is such that they will receive amateur, broadcasting, ship and
+      shore Navy, commercial, Arlington's time and all other stations using <i>spark
+      telegraph damped waves</i> or <i>arc</i> or <i>vacuum tube telephone
+      continuous waves</i> but not <i>continuous wave telegraph signals</i>,
+      unless these have been broken up into groups at the transmitting station.
+      To receive continuous wave telegraph signals requires receiving sets of
+      special kind and these will be described in the next chapter.
+    </p>
+    <p>
+      <i>Intermediate Wave Receiving Sets</i>.--There are two chief schemes
+      employed to increase the range of wave lengths that a set can receive and
+      these are by using: (1) <i>loading coils</i> and <i>shunt condensers</i>,
+      and (2) <i>bank-wound coils</i> and <i>variable condensers</i>. If you
+      have a short-wave set and plan to receive intermediate waves with it then
+      loading coils and fixed condensers shunted around them affords you the way
+      to do it, but if you prefer to buy a new receptor then the better way is
+      to get one with bank-wound coils and variable condensers; this latter way
+      preserves the electrical balance of the oscillation circuits better, the
+      electrical losses are less and the tuning easier and sharper.
+    </p>
+    <p>
+      <i>Intermediate Wave Set With Loading Coils.</i>--For this intermediate
+      wave set you can use either of the short-wave sets described in the
+      foregoing chapter. For the loading coils use <i>honeycomb coils</i>, or
+      other good compact inductance coils, as shown in <a href="#chap10">Chapter
+      X</a> and having a range of whatever wave length you wish to receive. The
+      following table shows the range of wave length of the various sized coils
+      when used with a variable condenser having a .001 microfarad <i>capacitance</i>,
+      the approximate <i>inductance</i> of each coil in <i>millihenries</i> and
+      prices at the present writing:
+    </p>
+    <h3>
+      TABLE OF CHARACTERISTICS OF HONEYCOMB COILS
+    </h3>
+<pre xml:space="preserve">
+                     Approximate Wave
+                   Length in Meters in
+
+  Millihenries
+  Inductance         .001 mfd. Variable           Mounted
+    Appx.              Air Condenser.            on Plug
+
+     .040                130--  375               $1.40
+     .075                180--  515                1.40
+     .15                 240--  730                1.50
+     .3                  330-- 1030                1.50
+     .6                  450-- 1460                1.55
+    1.3                  660-- 2200                1.60
+    2.3                  930-- 2850                1.65
+    4.5                 1300-- 4000                1.70
+    6.5                 1550-- 4800                1.75
+   11.                  2050-- 6300                1.80
+   20.                  3000-- 8500                2.00
+   40.                  4000--12000                2.15
+   65.                  5000--15000                2.35
+  100.                  6200--19000                2.60
+  125.                  7000--21000                3.00
+  175.                  8200--24000                3.50
+</pre>
+    <p>
+      These and other kinds of compact coils can be bought at electrical supply
+      houses that sell wireless goods. If your aerial is not very high or long
+      you can use loading coils, but to get anything like efficient results with
+      them you must have an aerial of large capacitance and the only way to get
+      this is to put up a high and long one with two or more parallel wires
+      spaced a goodly distance apart.
+    </p>
+    <p>
+      <i>The Parts and How to Connect Them Up</i>.--Get (1) <i>two honeycomb or
+      other coils</i> of the greatest wave length you want to receive, for in
+      order to properly balance the aerial, or primary oscillation circuit, and
+      the closed, or secondary oscillation circuit, you have to tune them to the
+      same wave length; (2) two <i>.001 mfd. variable condensers</i>, though
+      fixed condensers will do, and (3) two small <i>single-throw double-pole
+      knife switches</i> mounted on porcelain bases.
+    </p>
+    <p>
+      To use the loading coils all you have to do is to connect one of them in
+      the aerial above the primary coil of the loose coupler, or variocoupler as
+      shown in the wiring diagram in <i>Fig. 57</i>, then shunt one of the
+      condensers around it and connect one of the switches around this; this
+      switch enables you to cut in or out the loading coil at will. Likewise
+      connect the other loading coil in one side of the closed, or secondary
+      circuit between the variable .0007 mfd. condenser and the secondary coil
+      of the loose coupler or variocoupler as shown in <i>Fig. 53</i>. The other
+      connections are exactly the same as shown in <i>Figs. 44 and 45</i>.
+    </p>
+    <p>
+      <a name="fig057" id="fig057"><img width="600" height="638"
+      src="images/fig057.jpg"
+      alt="Fig. 57.--Wiring Diagram Showing Fixed Loading Coils for Intermediate Wave Set." />
+      </a>
+    </p>
+    <p>
+      <i>An Intermediate Wave Set With Variocoupler Inductance Coils</i>.--By
+      using the coil wound on the rotor of the variocoupler as the tickler the
+      coupling between the detector tube circuits and the aerial wire system
+      increases as the set is tuned for greater wave lengths. This scheme makes
+      the control of the regenerative circuit far more stable than it is where
+      an ordinary loose coupled tuning coil is used.
+    </p>
+    <p>
+      When the variocoupler is adjusted for receiving very long waves the rotor
+      sets at right angles to the stator and, since when it is in this position
+      there is no mutual induction between them, the tickler coil serves as a
+      loading coil for the detector plate oscillation circuit. Inductance coils
+      for short wave lengths are usually wound in single layers but <i>bank-wound
+      coils</i>, as they are called are necessary to get compactness where long
+      wave lengths are to be received. By winding inductance coils with two or
+      more layers the highest inductance values can be obtained with the least
+      resistance. A wiring diagram of a multipoint inductance coil is shown in
+      <i>Fig. 58</i>. You can buy this intermediate wave set assembled and ready
+      to use or get the parts and connect them up yourself.
+    </p>
+    <p>
+      <a name="fig058" id="fig058"><img width="600" height="469"
+      src="images/fig058.jpg"
+      alt="Fig. 58.--Wiring Diagram for Intermediate Wave Receptor with one Variocoupler and 12 section Bank-wound Inductance Coil." />
+      </a>
+    </p>
+    <p>
+      <i>The Parts and How to Connect Them Up.</i>--For this regenerative
+      intermediate wave set get: (1) one <i>12 section triple bank-wound
+      inductance coil</i>, (2) one <i>variometer</i>, and (3) all the other
+      parts shown in the diagram <i>Fig. 58</i> except the variocoupler. First
+      connect the free end of the condenser in the aerial to one of the
+      terminals of the stator of the variocoupler; then connect the other
+      terminal of the stator with one of the ends of the bank-wound inductance
+      coil and connect the movable contact of this with the ground.
+    </p>
+    <p>
+      Next connect a wire to the aerial between the variable condenser and the
+      stator and connect this to one post of a .0005 microfarad fixed condenser,
+      then connect the other post of this with the grid of the detector and
+      shunt a 2 megohm grid leak around it. Connect a wire to the ground wire
+      between the bank-wound inductance coil and the ground proper, <i>i.e.</i>,
+      the radiator or water pipe, connect the other end of this to the +
+      electrode of the <i>A</i> battery and connect this end also to one of the
+      terminals of the filament. This done connect the other terminal of the
+      filament to one post of the rheostat and the other post of this to the -
+      or negative side of the <i>A</i> battery.
+    </p>
+    <p>
+      To the + electrode of the <i>A</i> battery connect the - or zinc pole of
+      the <i>B</i> battery and connect the + or carbon pole of the latter with
+      one post of the fixed .001 microfarad condenser. This done connect one
+      terminal of the tickler coil which is on the rotor of the variometer to
+      the plate of the detector and the other terminal of the tickler to the
+      other post of the .001 condenser and around this shunt your headphones. Or
+      if you want to use one or more amplifying tubes connect the circuit of the
+      first one, see <i>Fig. 45</i>, to the posts on either side of the fixed
+      condenser instead of the headphones.
+    </p>
+    <p>
+      <i>A Long Wave Receiving Set.</i>--The vivid imagination of Jules Verne
+      never conceived anything so fascinating as the reception of messages
+      without wires sent out by stations half way round the world; and in these
+      days of high power cableless stations on the five continents you can
+      listen-in to the messages and hear what is being sent out by the Lyons,
+      Paris and other French stations, by Great Britain, Italy, Germany and even
+      far off Russia and Japan.
+    </p>
+    <p>
+      A long wave set for receiving these stations must be able to tune to wave
+      lengths up to 20,000 meters. Differing from the way in which the
+      regenerative action of the short wave sets described in the preceding
+      chapter is secured and which depends on a tickler coil and the coupling
+      action of the detector in this long wave set, [Footnote: All of the short
+      wave and intermediate wave receivers described, are connected up according
+      to the wiring diagram used by the A. H. Grebe Company, Richmond Hill, Long
+      Island, N. Y.] this action is obtained by the use of a tickler coil in the
+      plate circuit which is inductively coupled to the grid circuit and this
+      feeds back the necessary amount of current. This is a very good way to
+      connect up the circuits for the reason that: (1) the wiring is simplified,
+      and (2) it gives a single variable adjustment for the entire range of wave
+      lengths the receptor is intended to cover.
+    </p>
+    <p>
+      <i>The Parts and How to Connect Them Up.</i>--The two chief features as
+      far as the parts are concerned of this long wave length receiving set are
+      (1) the <i>variable condensers</i>, and (2) the <i>tuning inductance coils</i>.
+      The variable condenser used in series with the aerial wire system has 26
+      plates and is equal to a capacitance of <i>.0008 mfd.</i> which is the
+      normal aerial capacitance. The condenser used in the secondary coil
+      circuit has 14 plates and this is equal to a capacitance of <i>.0004 mfd</i>.
+    </p>
+    <p>
+      There are a number of inductance coils and these are arranged so that they
+      can be connected in or cut out and combinations are thus formed which give
+      a high efficiency and yet allow them to be compactly mounted. The
+      inductance coils of the aerial wire system and those of the secondary coil
+      circuit are practically alike. For wave lengths up to 2,200 meters <i>bank
+      litz-wound coils</i> are used and these are wound up in 2, 4 and 6 banks
+      in order to give the proper degree of coupling and inductance values.
+    </p>
+    <p>
+      Where wave lengths of more than 2,200 meters are to be received <i>coto-coils</i>
+      are used as these are the "last word" in inductance coil design, and are
+      especially adapted for medium as well as long wave lengths. [Footnote: Can
+      be had of the Coto Coil Co., Providence, R. I.] These various coils are
+      cut in and out by means of two five-point switches which are provided with
+      auxiliary levers and contactors for <i>dead-ending</i> the right amount of
+      the coils. In cutting in coils for increased wave lengths, that is from
+      10,000 to 20,000 meters, all of the coils of the aerial are connected in
+      series as well as all of the coils of the secondary circuit. The
+      connections for a long wave receptor are shown in the wiring diagram in <i>Fig.
+      59</i>.
+    </p>
+    <p>
+      <a name="fig059" id="fig059"><img width="600" height="427"
+      src="images/fig059.jpg"
+      alt="Fig. 59.--Wiring Diagram Showing Long Wave Receptor with Variocouplers and Bank-wound Inductance Coils" />
+      </a>
+    </p>
+    <h2>
+      <a name="chap13" id="chap13">CHAPTER XIII</a>
+    </h2>
+    <h3>
+      HETERODYNE OR BEAT LONG WAVE TELEGRAPH RECEIVING SET
+    </h3>
+    <p>
+      Any of the receiving sets described in the foregoing chapters will respond
+      to either: (1) a wireless telegraph transmitter that uses a spark gap and
+      which sends out periodic electric waves, or to (2) a wireless telephone
+      transmitter that uses an arc or a vacuum tube oscillator and which sends
+      out continuous electric waves. To receive wireless <i>telegraph</i>
+      signals, however, from a transmitter that uses an arc or a vacuum tube
+      oscillator and which sends out continuous waves, either the transmitter or
+      the receptor must be so constructed that the continuous waves will be
+      broken up into groups of audio frequency and this is done in several
+      different ways.
+    </p>
+    <p>
+      There are four different ways employed at the present time to break up the
+      continuous waves of a wireless telegraph transmitter into groups and these
+      are: (<i>a</i>) the <i>heterodyne</i>, or <i>beat</i>, method, in which
+      waves of different lengths are impressed on the received waves and so
+      produces beats; (<i>b</i>) the <i>tikker</i>, or <i>chopper</i> method, in
+      which the high frequency currents are rapidly broken up; (<i>c</i>) the
+      variable condenser method, in which the movable plates are made to rapidly
+      rotate; (<i>d</i>) the <i>tone wheel</i>, or <i>frequency transformer</i>,
+      as it is often called, and which is really a modified form of and an
+      improvement on the tikker. The heterodyne method will be described in this
+      chapter.
+    </p>
+    <p>
+      <i>What the Heterodyne or Beat Method Is.</i>--The word <i>heterodyne</i>
+      was coined from the Greek words <i>heteros</i> which means <i>other</i>,
+      or <i>different</i>, and <i>dyne</i> which means <i>power</i>; in other
+      words it means when used in connection with a wireless receptor that
+      another and different high frequency current is used besides the one that
+      is received from the sending station. In music a <i>beat</i> means a
+      regularly recurrent swelling caused by the reinforcement of a sound and
+      this is set up by the interference of sound waves which have slightly
+      different periods of vibration as, for instance, when two tones take place
+      that are not quite in tune with each other. This, then, is the principle
+      of the heterodyne, or beat, receptor.
+    </p>
+    <p>
+      In the heterodyne, or beat method, separate sustained oscillations, that
+      are just about as strong as those of the incoming waves, are set up in the
+      receiving circuits and their frequency is just a little higher or a little
+      lower than those that are set up by the waves received from the distant
+      transmitter. The result is that these oscillations of different
+      frequencies interfere and reinforce each other when <i>beats</i> are
+      produced, the period of which is slow enough to be heard in the
+      headphones, hence the incoming signals can be heard only when waves from
+      the sending station are being received. A fuller explanation of how this
+      is done will be found in <a href="#chap15">Chapter XV</a>.
+    </p>
+    <p>
+      <i>The Autodyne or Self-Heterodyne Long-Wave Receiving Set.</i>--This is
+      the simplest type of heterodyne receptor and it will receive periodic
+      waves from spark telegraph transmitters or continuous waves from an arc or
+      vacuum tube telegraph transmitter. In this type of receptor the detector
+      tube itself is made to set up the <i>heterodyne oscillations</i> which
+      interfere with those that are produced by the incoming waves that are a
+      little out of tune with it.
+    </p>
+    <p>
+      With a long wave <i>autodyne</i>, or <i>self-heterodyne</i> receptor, as
+      this type is called, and a two-step audio-frequency amplifier you can
+      clearly hear many of the cableless stations of Europe and others that send
+      out long waves. For receiving long wave stations, however, you must have a
+      long aerial--a single wire 200 or more feet in length will do--and the
+      higher it is the louder will be the signals. Where it is not possible to
+      put the aerial up a hundred feet or more above the ground, you can use a
+      lower one and still get messages in <i>International Morse</i> fairly
+      strong.
+    </p>
+    <p>
+      <i>The Parts and Connections of an Autodyne, or Self-Heterodyne, Receiving
+      Set.</i>--For this long wave receiving set you will need: (1) one <i>variocoupler</i>
+      with the primary coil wound on the stator and the secondary coil and
+      tickler coil wound on the rotor, or you can use three honeycomb or other
+      good compact coils of the longest wave you want to receive, a table of
+      which is given in <a href="#chap07">Chapter XII</a>; (2) two <i>.001 mfd.
+      variable condensers</i>; (3) one <i>.0005 mfd. variable condenser</i>; (4)
+      one <i>.5 to 2 megohm grid leak resistance</i>; (5) one <i>vacuum tube
+      detector</i>; (6) one <i>A battery</i>; (7) one <i>rheostat</i>; (8) one
+      <i>B battery</i>; (9) one <i>potentiometer</i>; (10) one <i>.001 mfd.
+      fixed condenser</i> and (11) one pair of <i>headphones</i>. For the
+      two-step amplifier you must, of course, have besides the above parts the
+      amplifier tubes, variable condensers, batteries rheostats, potentiometers
+      and fixed condensers as explained in <a href="#chap09">Chapter IX</a>. The
+      connections for the autodyne, or self-heterodyne, receiving set are shown
+      in <i>Fig. 60</i>.
+    </p>
+    <p>
+      <a name="fig060" id="fig060"><img width="600" height="446"
+      src="images/fig060.jpg"
+      alt="Fig. 60.--Wiring Diagram of Long Wave Antodyne, or Self-Heterodyne Receptor." />
+      </a>
+    </p>
+    <p>
+      <i>The Separate Heterodyne Long Wave Receiving Set.</i>--This is a better
+      long wave receptor than the self heterodyne set described above for
+      receiving wireless telegraph signals sent out by a continuous long wave
+      transmitter. The great advantage of using a separate vacuum tube to
+      generate the heterodyne oscillations is that you can make the frequency of
+      the oscillations just what you want it to be and hence you can make it a
+      little higher or a little lower than the oscillations set up by the
+      received waves.
+    </p>
+    <p>
+      <i>The Parts and Connections of a Separate Heterodyne Long Wave Receiving
+      Set.</i>--The parts required for this long wave receiving set are: (1)
+      four honeycomb or other good <i>compact inductance</i> coils of the
+      longest wave length that you want to receive; (2) three <i>.001 mfd.
+      variable condensers</i>; (3) one <i>.0005 mfd. variable condenser</i>; (4)
+      one <i>1 megohm grid leak resistance</i>; (5) one <i>vacuum tube detector</i>;
+      (6) one <i>A battery</i>; (7) two rheostats; (8) two <i>B batteries</i>,
+      one of which is supplied with taps; (9) one <i>potentiometer</i>; (10) one
+      <i>vacuum tube amplifier</i>, for setting up the heterodyne oscillations;
+      (11) a pair of <i>headphones</i> and (12) all of the parts for a <i>two-step
+      amplifier</i> as detailed in <a href="#chap09">Chapter IX</a>, that is if
+      you are going to use amplifiers. The connections are shown in <i>Fig. 61</i>.
+    </p>
+    <p>
+      <a name="fig061" id="fig061"><img width="600" height="571"
+      src="images/fig061.jpg"
+      alt="Fig. 61.--Wiring Diagram of Long Wave Separate Heterodyne Receiving Set." />
+      </a>
+    </p>
+    <p>
+      In using either of these heterodyne receivers be sure to carefully adjust
+      the <i>B</i> battery by means of the potentiometer.
+    </p>
+    <p>
+      [Footnote: The amplifier tube in this case is used as a generator of
+      oscillations.]
+    </p>
+    <h2>
+      <a name="chap14" id="chap14">CHAPTER XIV</a>
+    </h2>
+    <h3>
+      HEADPHONES AND LOUD SPEAKERS
+    </h3>
+    <p>
+      <i>Wireless Headphones.</i>--A telephone receiver for a wireless receiving
+      set is made exactly on the same principle as an ordinary Bell telephone
+      receiver. The only difference between them is that the former is made flat
+      and compact so that a pair of them can be fastened together with a band
+      and worn on the head (when it is called a <i>headset</i>), while the
+      latter is long and cylindrical so that it can be held to the ear. A
+      further difference between them is that the wireless headphone is made as
+      sensitive as possible so that it will respond to very feeble currents,
+      while the ordinary telephone receiver is far from being sensitive and will
+      respond only to comparatively large currents.
+    </p>
+    <p>
+      <i>How a Bell Telephone Receiver Is Made.</i>--An ordinary telephone
+      receiver consists of three chief parts and these are: (1) a hard-rubber,
+      or composition, shell and cap, (2) a permanent steel bar magnet on one end
+      of which is wound a coil of fine insulated copper wire, and (3) a soft
+      iron disk, or <i>diaphragm</i>, all of which are shown in the
+      cross-section in <i>Fig. 62</i>. The bar magnet is securely fixed inside
+      of the handle so that the outside end comes to within about 1/32 of an
+      inch of the diaphragm when this is laid on top of the shell and the cap is
+      screwed on.
+    </p>
+    <p>
+      <a name="fig062" id="fig062"><img width="586" height="400"
+      src="images/fig062.jpg"
+      alt="Fig. 62.--Cross-section of Bell telephone Receiver." /></a>
+    </p>
+    <table cellspacing="20" summary="Illustration">
+      <tr>
+        <td align="center">
+          <i>Photograph unavailable</i>
+        </td>
+      </tr>
+      <tr>
+        <td align="center">
+          original &copy; Underwood and Underwood.<br /> Alexander Graham Bell,
+          Inventor of the Telephone, now an ardent Radio Enthusiast.
+        </td>
+      </tr>
+    </table>
+    <p>
+      The ends of the coil of wire are connected with two binding posts which
+      are in the end of the shell, but are shown in the picture at the sides for
+      the sake of clearness. This coil usually has a resistance of about 75 ohms
+      and the meaning of the <i>ohmic resistance</i> of a receiver and its
+      bearing on the sensitiveness of it will be explained a little farther
+      along. After the disk, or diaphragm, which is generally made of thin, soft
+      sheet iron that has been tinned or japanned, [Footnote: A disk of
+      photographic tin-type plate is generally used.] is placed over the end of
+      the magnet, the cap, which has a small opening in it, is screwed on and
+      the receiver is ready to use.
+    </p>
+    <p>
+      <i>How a Wireless Headphone Is Made.</i>--For wireless work a receiver of
+      the watch-case type is used and nearly always two such receivers are
+      connected with a headband. It consists of a permanent bar magnet bent so
+      that it will fit into the shell of the receiver as shown at <i>A</i> in <i>Fig.
+      63</i>.
+    </p>
+    <p>
+      <a name="fig063" id="fig063"><img width="320" height="397"
+      src="images/fig063.jpg" alt="Fig. 63.--Wireless Headphone." /></a>
+    </p>
+    <p>
+      The ends of this magnet, which are called <i>poles</i>, are bent up, and
+      hence this type is called a <i>bipolar</i> receiver. The magnets are wound
+      with fine insulated wire as before and the diaphragm is held securely in
+      place over them by screwing on the cap.
+    </p>
+    <p>
+      <i>About Resistance, Turns of Wire and Sensitivity of Headphones.</i>--If
+      you are a beginner in wireless you will hear those who are experienced
+      speak of a telephone receiver as having a resistance of 75 ohms, 1,000
+      ohms, 2,000 or 3,000 ohms, as the case may be; from this you will gather
+      that the higher the resistance of the wire on the magnets the more
+      sensitive the receiver is. In a sense this is true, but it is not the
+      resistance of the magnet coils that makes it sensitive, in fact, it cuts
+      down the current, but it is the <i>number of turns</i> of wire on them
+      that determines its sensitiveness; it is easy to see that this is so, for
+      the larger the number of turns the more often will the same current flow
+      round the cores of the magnet and so magnetize them to a greater extent.
+    </p>
+    <p>
+      But to wind a large number of turns of wire close enough to the cores to
+      be effective the wire must be very small and so, of course, the higher the
+      resistance will be. Now the wire used for winding good receivers is
+      usually No. 40, and this has a diameter of .0031 inch; consequently, when
+      you know the ohmic resistance you get an idea of the number of turns of
+      wire and from this you gather in a general way what the sensitivity of the
+      receiver is.
+    </p>
+    <p>
+      A receiver that is sensitive enough for wireless work should be wound to
+      not less than 1,000 ohms (this means each ear phone), while those of a
+      better grade are wound to as high as 3,000 ohms for each one. A high-grade
+      headset is shown in <i>Fig. 64</i>. Each phone of a headset should be
+      wound to the same resistance, and these are connected in series as shown.
+      Where two or more headsets are used with one wireless receiving set they
+      must all be of the same resistance and connected in series, that is, the
+      coils of one head set are connected with the coils of the next head set
+      and so on to form a continuous circuit.
+    </p>
+    <p>
+      <a name="fig064" id="fig064"><img width="549" height="360"
+      src="images/fig064.jpg" alt="Fig. 64.--Wireless Headphone." /></a>
+    </p>
+    <p>
+      <i>The Impedance of Headphones.</i>--When a current is flowing through a
+      circuit the material of which the wire is made not only opposes its
+      passage--this is called its <i>ohmic resistance</i>--but a <i>counter-electromotive
+      force</i> to the current is set up due to the inductive effects of the
+      current on itself and this is called <i>impedance</i>. Where a wire is
+      wound in a coil the impedance of the circuit is increased and where an
+      alternating current is used the impedance grows greater as the frequency
+      gets higher. The impedance of the magnet coils of a receiver is so great
+      for high frequency oscillations that the latter cannot pass through them;
+      in other words, they are choked off.
+    </p>
+    <p>
+      <i>How the Headphones Work.</i>--As you will see from the cross-sections
+      in <i>Figs. 62</i> and <i>63</i> there is no connection, electrical or
+      mechanical, between the diaphragm and the other parts of the receiver. Now
+      when either feeble oscillations, which have been rectified by a detector,
+      or small currents from a <i>B</i> battery, flow through the magnet coils
+      the permanent steel magnet is energized to a greater extent than when no
+      current is flowing through it. This added magnetic energy makes the magnet
+      attract the diaphragm more than it would do by its own force. If, on the
+      other hand, the current is cut off the pull of the magnet is lessened and
+      as its attraction for the diaphragm is decreased the latter springs back
+      to its original position. When varying currents flow through the coils the
+      diaphragm vibrates accordingly and sends out sound waves.
+    </p>
+    <p>
+      <i>About Loud Speakers.</i>--The simplest acoustic instrument ever
+      invented is the <i>megaphone</i>, which latter is a Greek word meaning <i>great
+      sound</i>. It is a very primitive device and our Indians made it out of
+      birch-bark before Columbus discovered America. In its simplest form it
+      consists of a cone-shaped horn and as the speaker talks into the small end
+      the concentrated sound waves pass out of the large end in whatever
+      direction it is held.
+    </p>
+    <p>
+      Now a loud speaker of whatever kind consists of two chief parts and these
+      are: (1) a <i>telephone receiver</i>, and (2) a <i>megaphone</i>, or <i>horn</i>
+      as it is called. A loud speaker when connected with a wireless receiving
+      set makes it possible for a room, or an auditorium, full of people, or an
+      outdoor crowd, to hear what is being sent out by a distant station instead
+      of being limited to a few persons listening-in with headphones. To use a
+      loud speaker you should have a vacuum tube detector receiving set and this
+      must be provided with a one-step amplifier at least.
+    </p>
+    <p>
+      To get really good results you need a two-step amplifier and then energize
+      the plate of the second vacuum tube amplifier with a 100 volt <i>B</i>
+      battery; or if you have a three-step amplifier then use the high voltage
+      on the plate of the third amplifier tube. Amplifying tubes are made to
+      stand a plate potential of 100 volts and this is the kind you must use.
+      Now it may seem curious, but when the current flows through the coils of
+      the telephone receiver in one direction it gives better results than when
+      it flows through in the other direction; to find out the way the current
+      gives the best results try it out both ways and this you can do by simply
+      reversing the connections.
+    </p>
+    <p>
+      <i>The Simplest Type of Loud Speaker.</i>--This loud speaker, which is
+      called, the Arkay, [Footnote: Made by the Riley-Klotz Mfg. Co., Newark, N.
+      J.] will work on a one- or two-step amplifier. It consists of a brass horn
+      with a curve in it and in the bottom there is an adapter, or frame, with a
+      set screw in it so that you can fit in one of your headphones and this is
+      all there is to it. The construction is rigid enough to prevent overtones,
+      or distortion of speech or music. It is shown in <i>Fig. 65</i>.
+    </p>
+    <p>
+      <a name="fig065" id="fig065"><img width="280" height="325"
+      src="images/fig065.jpg" alt="Fig. 65.--Arkay Loud Speaker." /></a>
+    </p>
+    <p>
+      <i>Another Simple Kind of Loud Speaker.</i>--Another loud speaker, see <i>Fig.
+      66</i>, is known as the <i>Amplitone</i> [Footnote: Made by the American
+      Pattern, Foundry and Machine Co., 82 Church Street, N. Y. C.] and it
+      likewise makes use of the headphones as the sound producer. This device
+      has a cast metal horn which improves the quality of the sound, and all you
+      have to do is to slip the headphones on the inlet tubes of the horn and it
+      is ready for use. The two headphones not only give a longer volume of
+      sound than where a single one is used but there is a certain blended
+      quality which results from one phone smoothing out the imperfections of
+      the other.
+    </p>
+    <p>
+      <a name="fig066" id="fig066"><img width="280" height="312"
+      src="images/fig066.jpg" alt="Fig. 66.--Amplitone Loud Speaker." /></a>
+    </p>
+    <p>
+      <i>A Third Kind of Simple Loud Speaker.</i>--The operation of the <i>Amplitron</i>,
+      [Footnote: Made by the Radio Service Co., 110 W. 40th Street, N. Y.] as
+      this loud speaker is called, is slightly different from others used for
+      the same purpose. The sounds set up by the headphone are conveyed to the
+      apex of an inverted copper cone which is 7 inches long and 10 inches in
+      diameter. Here it is reflected by a parabolic mirror which greatly
+      amplifies the sounds. The amplification takes place without distortion,
+      the sounds remaining as clear and crisp as when projected by the
+      transmitting station. By removing the cap from the receiver the shell is
+      screwed into a receptacle on the end of the loud speaker and the
+      instrument is ready for use. It is pictured in <i>Fig. 67</i>.
+    </p>
+    <p>
+      <a name="fig067" id="fig067"><img width="400" height="390"
+      src="images/fig067.jpg" alt="Fig. 67.--Amplitron Loud Speaker." /></a>
+    </p>
+    <p>
+      <i>A Super Loud Speaker.</i>--This loud speaker, which is known as the <i>Magnavox
+      Telemegafone</i>, was the instrument used by Lt. Herbert E. Metcalf, 3,000
+      feet in the air, and which startled the City of Washington on April 2,
+      1919, by repeating President Wilson's <i>Victory Loan Message</i> from an
+      airplane in flight so that it was distinctly heard by 20,000 people below.
+    </p>
+    <p>
+      This wonderful achievement was accomplished through the installation of
+      the <i>Magnavox</i> and amplifiers in front of the Treasury Building.
+      Every word Lt. Metcalf spoke into his wireless telephone transmitter was
+      caught and swelled in volume by the <i>Telemegafones</i> below and persons
+      blocks away could hear the message plainly. Two kinds of these loud
+      speakers are made and these are: (1) a small loud speaker for the use of
+      operators so that headphones need not be worn, and (2) a large loud
+      speaker for auditorium and out-door audiences.
+    </p>
+    <table cellspacing="20" summary="Illustration">
+      <tr>
+        <td align="center">
+          <i>Photograph unavailable</i>
+        </td>
+      </tr>
+      <tr>
+        <td align="center">
+          original &copy; Underwood and Underwood.<br /> World's Largest Loud
+          Speaker ever made. Installed in Lytle Park, Cincinnati, Ohio, to
+          permit President Harding's Address at Point Pleasant, Ohio, during the
+          Grant Centenary Celebration to be heard within a radius of one square.
+        </td>
+      </tr>
+    </table>
+    <p>
+      Either kind may be used with a one- or two-step amplifier or with a
+      cascade of half a dozen amplifiers, according to the degree of loudness
+      desired. The <i>Telemegafone</i> itself is not an amplifier in the true
+      sense inasmuch as it contains no elements which will locally increase the
+      incoming current. It does, however, transform the variable electric
+      currents of the wireless receiving set into sound vibrations in a most
+      wonderful manner.
+    </p>
+    <p>
+      A <i>telemegafone</i> of either kind is formed of: (1) a telephone
+      receiver of large proportions, (2) a step-down induction coil, and (3) a 6
+      volt storage battery that energizes a powerful electromagnet which works
+      the diaphragm. An electromagnet is used instead of a permanent magnet and
+      this is energized by a 6-volt storage battery as shown in the wiring
+      diagram at <i>A</i> in <i>Fig. 68</i>. One end of the core of this magnet
+      is fixed to the iron case of the speaker and together these form the
+      equivalent of a horseshoe magnet. A movable coil of wire is supported from
+      the center of the diaphragm the edge of which is rigidly held between the
+      case and the small end of the horn. This coil is placed over the upper end
+      of the magnet and its terminals are connected to the secondary of the
+      induction coil. Now when the coil is energized by the current from the
+      amplifiers it and the core act like a solenoid in that the coil tends to
+      suck the core into it; but since the core is fixed and the coil is movable
+      the core draws the coil down instead. The result is that with every
+      variation of the current that flows through the coil it moves up and down
+      and pulls and pushes the diaphragm down and up with it. The large
+      amplitude of the vibrations of the latter set up powerful sound waves
+      which can be heard several blocks away from the horn. In this way then are
+      the faint incoming signals, speech and music which are received by the
+      amplifying receiving set reproduced and magnified enormously. The <i>Telemegafone</i>
+      is shown complete at <i>B</i>.
+    </p>
+    <p>
+      <a name="fig068" id="fig068"><img width="600" height="517"
+      src="images/fig068.jpg" alt="Fig. 68.--Magnavox Loud Speaker." /></a>
+    </p>
+    <h2>
+      <a name="chap15" id="chap15">CHAPTER XV</a>
+    </h2>
+    <h3>
+      OPERATION OF VACUUM TUBE RECEPTORS
+    </h3>
+    <p>
+      From the foregoing chapters you have seen that the vacuum tube can be used
+      either as a <i>detector</i> or an <i>amplifier</i> or as a <i>generator</i>
+      of electric oscillations, as in the case of the heterodyne receiving set.
+      To understand how a vacuum tube acts as a detector and as an amplifier you
+      must first know what <i>electrons</i> are. The way in which the vacuum
+      tube sets up sustained oscillations will be explained in <a href="#chap18">Chapter
+      XVIII</a> in connection with the <i>Operation of Vacuum Tube Transmitters</i>.
+    </p>
+    <p>
+      <i>What Electrons Are.</i>--Science teaches us that masses of matter are
+      made up of <i>molecules</i>, that each of these is made up of <i>atoms</i>,
+      and each of these, in turn, is made up of a central core of positive
+      particles of electricity surrounded by negative particles of electricity
+      as shown in the schematic diagram, <i>Fig. 69</i>. The little black
+      circles inside the large circle represent <i>positive particles of
+      electricity</i> and the little white circles outside of the large circle
+      represent <i>negative particles of electricity</i>, or <i>electrons</i> as
+      they are called.
+    </p>
+    <p>
+      <a name="fig069" id="fig069"><img width="600" height="410"
+      src="images/fig069.jpg" alt="Fig. 69.--Schematic Diagram of an Atom." /></a>
+    </p>
+    <p>
+      It is the number of positive particles of electricity an atom has that
+      determines the kind of an element that is formed when enough atoms of the
+      same kind are joined together to build it up. Thus hydrogen, which is the
+      lightest known element, has one positive particle for its nucleus, while
+      uranium, the heaviest element now known, has 92 positive particles. Now
+      before leaving the atom please note that it is as much smaller than the
+      diagram as the latter is smaller than our solar system.
+    </p>
+    <p>
+      <i>What Is Meant by Ionization.</i>--A hydrogen atom is not only lighter
+      but it is smaller than the atom of any other element while an electron is
+      more than a thousand times smaller than the atom of which it is a part.
+      Now as long as all of the electrons remain attached to the surface of an
+      atom its positive and negative charges are equalized and it will,
+      therefore, be neither positive nor negative, that is, it will be perfectly
+      neutral. When, however, one or more of its electrons are separated from
+      it, and there are several ways by which this can be done, the atom will
+      show a positive charge and it is then called a <i>positive ion</i>.
+    </p>
+    <p>
+      In other words a <i>positive ion</i> is an atom that has lost some of its
+      negative electrons while a <i>negative ion</i> is one that has acquired
+      some additional negative <i>electrons</i>. When a number of electrons are
+      being constantly given by the atoms of an element, which let us suppose is
+      a metal, and are being attracted to atoms of another element, which we
+      will say is also a metal, a flow of electrons takes place between the two
+      oppositely charged elements and form a current of negative electricity as
+      represented by the arrows at <i>A</i> in <i>Fig. 70</i>.
+    </p>
+    <p>
+      <a name="fig070" id="fig070"><img width="600" height="277"
+      src="images/fig070.jpg"
+      alt="Fig. 70.--Action of Two-electrode Vacuum Tube." /></a>
+    </p>
+    <p>
+      When a stream of electrons is flowing between two metal elements, as a
+      filament and a plate in a vacuum tube detector, or an amplifier, they act
+      as <i>carriers</i> for more negative electrons and these are supplied by a
+      battery as we shall presently explain. It has always been customary for us
+      to think of a current of electricity as flowing from the positive pole of
+      a battery to the negative pole of it and hence we have called this the <i>direction
+      of the current</i>. Since the electronic theory has been evolved it has been
+      shown that the electrons, or negative charges of electricity, flow from
+      the negative to the positive pole and that the ionized atoms, which are
+      more positive than negative, flow in the opposite direction as shown at <i>B</i>.
+    </p>
+    <p>
+      <i>How Electrons are Separated from Atoms</i>.--The next question that
+      arises is how to make a metal throw off some of the electrons of the atoms
+      of which it is formed. There are several ways that this can be done but in
+      any event each atom must be given a good, hard blow. A simple way to do
+      this is to heat a metal to incandescence when the atoms will bombard each
+      other with terrific force and many of the electrons will be knocked off
+      and thrown out into the surrounding space.
+    </p>
+    <p>
+      But all, or nearly all, of them will return to the atoms from whence they
+      came unless a means of some kind is employed to attract them to the atoms
+      of some other element. This can be done by giving the latter piece of
+      metal a positive charge. If now these two pieces of metal are placed in a
+      bulb from which the air has been exhausted and the first piece of metal is
+      heated to brilliancy while the second piece of metal is kept positively
+      electrified then a stream of electrons will flow between them.
+    </p>
+    <p>
+      <i>Action of the Two Electrode Vacuum Tube.</i>--Now in a vacuum tube
+      detector a wire filament, like that of an incandescent lamp, is connected
+      with a battery and this forms the hot element from which the electrons are
+      thrown off, and a metal plate with a terminal wire secured to it is
+      connected to the positive or carbon tap of a dry battery; now connect the
+      negative or zinc tap of this with one end of a telephone receiver and the
+      other end of this with the terminals of the filament as shown at <i>A</i>
+      in <i>Fig. 71</i>. If now you heat the filament and hold the phone to your
+      ear you can hear the current from the <i>B</i> battery flowing through the
+      circuit.
+    </p>
+    <p>
+      <a name="fig071ab" id="fig071ab"><img width="600" height="321"
+      src="images/fig071ab.jpg"
+      alt="(A) and (B) Fig. 71.--How a Two Electrode Tube Acts as a Relay or a Detector." />
+      </a> <a name="fig071c" id="fig071c"><img width="600" height="396"
+      src="images/fig071c.jpg"
+      alt="(C) Fig. 71.--Only the Positive Part of Oscillations Goes through the Tube." />
+      </a>
+    </p>
+    <p>
+      Since the electrons are negative charges of electricity they are not only
+      thrown off by the hot wire but they are attracted by the positive charged
+      metal plate and when enough electrons pass, or flow, from the hot wire to
+      the plate they form a conducting path and so complete the circuit which
+      includes the filament, the plate and the <i>B</i> or plate battery, when
+      the current can then flow through it. As the number of electrons that are
+      thrown off by the filament is not great and the voltage of the plate is
+      not high the current that flows between the filament and the plate is
+      always quite small.
+    </p>
+    <p>
+      <i>How the Two Electrode Tube Acts as a Detector.</i>--As the action of a
+      two electrode tube as a detector [Footnote: The three electrode vacuum
+      tube has entirely taken the place of the two electrode type.] is simpler
+      than that of the three electrode vacuum tube we shall describe it first.
+      The two electrode vacuum tube was first made by Mr. Edison when he was
+      working on the incandescent lamp but that it would serve as a detector of
+      electric waves was discovered by Prof. Fleming, of Oxford University,
+      London. As a matter of fact, it is not really a detector of electric
+      waves, but it acts as: (1) a <i>rectifier</i> of the oscillations that are
+      set up in the receiving circuits, that is, it changes them into pulsating
+      direct currents so that they will flow through and affect a telephone
+      receiver, and (2) it acts as a <i>relay</i> and the feeble received
+      oscillating current controls the larger direct current from the <i>B</i>
+      battery in very much the same way that a telegraph relay does. This latter
+      relay action will be explained when we come to its operation as an
+      amplifier.
+    </p>
+    <p>
+      We have just learned that when the stream of electrons flow from the hot
+      wire to the cold positive plate in the tube they form a conducting path
+      through which the battery current can flow. Now when the electric
+      oscillations surge through the closed oscillation circuit, which includes
+      the secondary of the tuning coil, the variable condenser, the filament and
+      the plate as shown at <i>B</i> in <i>Fig. 71</i> the positive part of them
+      passes through the tube easily while the negative part cannot get through,
+      that is, the top, or positive, part of the wave-form remains intact while
+      the lower, or negative, part is cut off as shown in the diagram at <i>C</i>.
+      As the received oscillations are either broken up into wave trains of
+      audio frequency by the telegraph transmitter or are modulated by a
+      telephone transmitter they carry the larger impulses of the direct current
+      from the <i>B</i> battery along with them and these flow through the
+      headphones. This is the reason the vacuum tube amplifies as well as
+      detects.
+    </p>
+    <p>
+      <i>How the Three Electrode Tube Acts as a Detector.</i>--The vacuum tube
+      as a detector has been made very much more sensitive by the use of a third
+      electrode shown in <i>Fig. 72</i>. In this type of vacuum tube the third
+      electrode, or <i>grid</i>, is placed between the filament and the plate
+      and this controls the number of electrons flowing from the filament to the
+      plate; in passing between these two electrodes they have to go through the
+      holes formed by the grid wires.
+    </p>
+    <p>
+      <a name="fig072ab" id="fig072ab"><img width="600" height="359"
+      src="images/fig072ab.jpg"
+      alt="(A) and (B) Fig. 72.--How the Positive and Negative Voltages of Oscillations Act on the Electrons." />
+      </a> <a name="fig072c" id="fig072c"><img width="600" height="342"
+      src="images/fig072c.jpg"
+      alt="(C) Fig. 72.--How the Three Electrode Tube Acts as a Detector and Amplifier." />
+      </a> <a name="fig072d" id="fig072d"><img width="600" height="448"
+      src="images/fig072d.jpg"
+      alt="(D) Fig. 72.--How the Oscillations Control the Flow of the Battery Current through the Tube." />
+      </a>
+    </p>
+    <p>
+      If now the grid is charged to a higher <i>negative</i> voltage than the
+      filament the electrons will be stopped by the latter, see <i>A</i>, though
+      some of them will go through to the plate because they travel at a high
+      rate of speed. The higher the negative charge on the grid the smaller will
+      be the number of electrons that will reach the plate and, of course, the
+      smaller will be the amount of current that will flow through the tube and
+      the headphones from the <i>B</i> battery.
+    </p>
+    <p>
+      On the other hand if the grid is charged <i>positively</i>, see <i>B</i>,
+      then more electrons will strike the plate than when the grid is not used
+      or when it is negatively charged. But when the three electrode tube is
+      used as a detector the oscillations set up in the circuits change the grid
+      alternately from negative to positive as shown at <i>C</i> and hence the
+      voltage of the <i>B</i> battery current that is allowed to flow through
+      the detector from the plate to the filament rises and falls in unison with
+      the voltage of the oscillating currents. The way the positive and negative
+      voltages of the oscillations which are set up by the incoming waves,
+      energize the grid; how the oscillator tube clips off the negative parts of
+      them, and, finally, how these carry the battery current through the tube
+      are shown graphically by the curves at <i>D</i>.
+    </p>
+    <p>
+      <i>How the Vacuum Tube Acts as an Amplifier</i>.--If you connect up the
+      filament and the plate of a three electrode tube with the batteries and do
+      not connect in the grid, you will find that the electrons which are thrown
+      off by the filament will not get farther than the grid regardless of how
+      high the voltage is that you apply to the plate. This is due to the fact
+      that a large number of electrons which are thrown off by the filament
+      strike the grid and give it a negative charge, and consequently, they
+      cannot get any farther. Since the electrons do not reach the plate the
+      current from the <i>B</i> battery cannot flow between it and the filament.
+    </p>
+    <p>
+      Now with a properly designed amplifier tube a very small negative voltage
+      on the grid will keep a very large positive voltage on the plate from
+      sending a current through the tube, and oppositely, a very small positive
+      voltage on the grid will let a very large plate current flow through the
+      tube; this being true it follows that any small variation of the voltage
+      from positive to negative on the grid and the other way about will vary a
+      large current flowing from the plate to the filament.
+    </p>
+    <p>
+      In the Morse telegraph the relay permits the small current that is
+      received from the distant sending station to energize a pair of magnets,
+      and these draw an armature toward them and close a second circuit when a
+      large current from a local battery is available for working the sounder.
+      The amplifier tube is a variable relay in that the feeble currents set up
+      by the incoming waves constantly and proportionately vary a large current
+      that flows through the headphones. This then is the principle on which the
+      amplifying tube works.
+    </p>
+    <p>
+      <i>The Operation of a Simple Vacuum Tube Receiving Set</i>.--The way a
+      simple vacuum tube detector receiving set works is like this: when the
+      filament is heated to brilliancy it gives off electrons as previously
+      described. Now when the electric waves impinge on the aerial wire they set
+      up oscillations in it and these surge through the primary coil of the
+      loose coupled tuning coil, a diagram of which is shown at <i>B</i> in <i>Fig.
+      41</i>.
+    </p>
+    <p>
+      The energy of these oscillations sets up oscillations of the same
+      frequency in the secondary coil and these high frequency currents whose
+      voltage is first positive and then negative, surge in the closed circuit
+      which includes the secondary coil and the variable condenser. At the same
+      time the alternating positive and negative voltage of the oscillating
+      currents is impressed on the grid; at each change from + to - and back
+      again it allows the electrons to strike the plate and then shuts them off;
+      as the electrons form the conducting path between the filament and the
+      plate the larger direct current from the <i>B</i> battery is permitted to
+      flow through the detector tube and the headphones.
+    </p>
+    <p>
+      <i>Operation of a Regenerative Vacuum Tube Receiving Set</i>.--By feeding
+      back the pulsating direct current from the <i>B</i> battery through the
+      tickler coil it sets up other and stronger oscillations in the secondary
+      of the tuning coil when these act on the detector tube and increase its
+      sensitiveness to a remarkable extent. The regenerative, or <i>feed back</i>,
+      action of the receiving circuits used will be easily understood by
+      referring back to <i>B</i> in <i>Fig. 47</i>.
+    </p>
+    <p>
+      When the waves set up oscillations in the primary of the tuning coil the
+      energy of them produces like oscillations in the closed circuit which
+      includes the secondary coil and the condenser; the alternating positive
+      and negative voltages of these are impressed on the grid and these, as we
+      have seen before, cause similar variations of the direct current from the
+      <i>B</i> battery which acts on the plate and which flows between the
+      latter and the filament.
+    </p>
+    <p>
+      This varying direct current, however, is made to flow back through the
+      third, or tickler coil of the tuning coil and sets up in the secondary
+      coil and circuits other and larger oscillating currents and these augment
+      the action of the oscillations produced by the incoming waves. These extra
+      and larger currents which are the result of the feedback then act on the
+      grid and cause still larger variations of the current in the plate voltage
+      and hence of the current of the <i>B</i> battery that flows through the
+      detector and the headphones. At the same time the tube keeps on responding
+      to the feeble electric oscillations set up in the circuits by the incoming
+      waves. This regenerative action of the battery current augments the
+      original oscillations many times and hence produce sounds in the
+      headphones that are many times greater than where the vacuum tube detector
+      alone is used.
+    </p>
+    <p>
+      <i>Operation of Autodyne and Heterodyne Receiving Sets</i>.--On page <i>109</i>
+      [Chapter VII] we discussed and at <i>A</i> in <i>Fig. 36</i> is shown a
+      picture of two tuning forks mounted on sounding boxes to illustrate the
+      principle of electrical tuning. When a pair of these forks are made to
+      vibrate exactly the same number of times per second there will be a
+      condensation of the air between them and the sound waves that are sent out
+      will be augmented. But if you adjust one of the forks so that it will
+      vibrate 256 times a second and the other fork so that it will vibrate 260
+      times a second then there will be a phase difference between the two sets
+      of waves and the latter will augment each other 4 times every second and
+      you will hear these rising and falling sounds as <i>beats</i>.
+    </p>
+    <p>
+      Now electric oscillations set up in two circuits that are coupled together
+      act in exactly the same way as sound waves produced by two tuning forks
+      that are close to each other. Since this is true if you tune one of the
+      closed circuits so that the oscillations in it will have a frequency of a
+      1,000,000 and tune the other circuit so that the oscillations in it have a
+      frequency of 1,001,000 a second then the oscillations will augment each
+      other 1,000 times every second.
+    </p>
+    <p>
+      As these rising and falling currents act on the pulsating currents from
+      the B battery which flow through the detector tube and the headphones you
+      will hear them as beats. A graphic representation of the oscillating
+      currents set up by the incoming waves, those produced by the heterodyne
+      oscillator and the beats they form is shown in <i>Fig. 73</i>. To produce
+      these beats a receptor can use: (1) a single vacuum tube for setting up
+      oscillations of both frequencies when it is called an <i>autodyne</i>, or
+      <i>self-heterodyne</i> receptor, or (2) a separate vacuum tube for setting
+      up the oscillations for the second circuit when it is called a <i>heterodyne</i>
+      receptor.
+    </p>
+    <p>
+      <a name="fig073" id="fig073"><img width="600" height="680"
+      src="images/fig073.jpg" alt="Fig. 73.--How the Heterodyne Receptor Works." /></a>
+    </p>
+    <p>
+      <i>The Autodyne, or Self-Heterodyne Receiving Set</i>.--Where only one
+      vacuum tube is used for producing both frequencies you need only a
+      regenerative, or feed-back receptor; then you can tune the aerial wire
+      system to the incoming waves and tune the closed circuit of the secondary
+      coil so that it will be out of step with the former by 1,000 oscillations
+      per second, more or less, the exact number does not matter in the least.
+      From this you will see that any regenerative set can be used for autodyne,
+      or self-heterodyne, reception.
+    </p>
+    <p>
+      <i>The Separate Heterodyne Receiving Set.</i>--The better way, however, is
+      to use a separate vacuum tube for setting up the heterodyne oscillations.
+      The latter then act on the oscillations that are produced by the incoming
+      waves and which energize the grid of the detector tube. Note that the
+      vacuum tube used for producing the heterodyne oscillations is a <i>generator</i>
+      of electric oscillations; the latter are impressed on the detector
+      circuits through the variable coupling, the secondary of which is in
+      series with the aerial wire as shown in <i>Fig. 74</i>. The way in which
+      the tube acts as a generator of oscillations will be told in <a
+      href="#chap18">Chapter XVIII</a>.
+    </p>
+    <p>
+      <a name="fig074" id="fig074"><img width="461" height="400"
+      src="images/fig074.jpg" alt="Fig. 74.--Separate Heterodyne Oscillator." /></a>
+    </p>
+    <h2>
+      <a name="chap16" id="chap16">CHAPTER XVI</a>
+    </h2>
+    <h3>
+      CONTINUOUS WAVE TELEGRAPH TRANSMITTING SETS WITH DIRECT CURRENT
+    </h3>
+    <p>
+      In the first part of this book we learned about spark-gap telegraph sets
+      and how the oscillations they set up are <i>damped</i> and the waves they
+      send out are <i>periodic</i>. In this and the next chapter we shall find
+      out how vacuum tube telegraph transmitters are made and how they set up
+      oscillations that are <i>sustained</i> and radiate waves that are <i>continuous</i>.
+    </p>
+    <p>
+      Sending wireless telegraph messages by continuous waves has many features
+      to recommend it as against sending them by periodic waves and among the
+      most important of these are that the transmitter can be: (1) more sharply
+      tuned, (2) it will send signals farther with the same amount of power, and
+      (3) it is noiseless in operation. The disadvantageous features are that:
+      (1) a battery current is not satisfactory, (2) its circuits are somewhat
+      more complicated, and (3) the oscillator tubes burn out occasionally.
+      There is, however, a growing tendency among amateurs to use continuous
+      wave transmitters and they are certainly more up-to-date and interesting
+      than spark gap sets.
+    </p>
+    <p>
+      Now there are two practical ways by which continuous waves can be set up
+      for sending either telegraphic signals or telephonic speech and music and
+      these are with: (a) an <i>oscillation arc lamp</i>, and (b) a <i>vacuum
+      tube oscillator</i>. The oscillation arc was the earliest known way of
+      setting up sustained oscillations, and it is now largely used for
+      commercial high power, long distance work. But since the vacuum tube has
+      been developed to a high degree of efficiency and is the scheme that is
+      now in vogue for amateur stations we shall confine our efforts here to
+      explaining the apparatus necessary and how to wire the various parts
+      together to produce several sizes of vacuum tube telegraph transmitters.
+    </p>
+    <p>
+      <i>Sources of Current for Telegraph Transmitting Sets</i>.--Differing from
+      a spark-gap transmitter you cannot get any appreciable results with a low
+      voltage battery current to start with. For a purely experimental vacuum
+      tube telegraph transmitter you can use enough <i>B</i> batteries to
+      operate it but the current strength of these drops so fact when they are
+      in use, that they are not at all satisfactory for the work.
+    </p>
+    <p>
+      You can, however, use 110 volt direct current from a lighting circuit as
+      your initial source of power to energize the plate of the vacuum tube
+      oscillator of your experimental transmitter. Where you have a 110 volt <i>direct
+      current</i> lighting service in your home and you want a higher voltage
+      for your plate, you will then have to use a motor-generator set and this
+      costs money. If you have 110 volt <i>alternating current</i> lighting
+      service at hand your troubles are over so far as cost is concerned for you
+      can step it up to any voltage you want with a power transformer. In this
+      chapter will be shown how to use a direct current for your source of
+      initial power and in the next chapter how to use an alternating current
+      for the initial power.
+    </p>
+    <p>
+      <i>An Experimental Continuous Wave Telegraph Transmitter.</i>--You will
+      remember that in <a href="#chap15">Chapter XV</a> we learned how the
+      heterodyne receiver works and that in the separate heterodyne receiving
+      set the second vacuum tube is used solely to set up oscillations. Now
+      while this extra tube is used as a generator of oscillations these are, of
+      course, very weak and hence a detector tube cannot be used to generate
+      oscillations that are useful for other purposes than heterodyne receptors
+      and measurements.
+    </p>
+    <p>
+      There is a vacuum tube amplifier [Footnote: This is the <i>radiation</i>
+      UV-<i>201</i>, made by the Radio Corporation of America, Woolworth Bldg.,
+      New York City.] made that will stand a plate potential of 100 volts, and
+      this can be used as a generator of oscillations by energizing it with a
+      110 volt direct current from your lighting service. Or in a pinch you can
+      use five standard <i>B</i> batteries to develop the plate voltage, but
+      these will soon run down. But whatever you do, never use a current from a
+      lighting circuit on a tube of any kind that has a rated plate potential of
+      less than 100 volts.
+    </p>
+    <p>
+      <i>The Apparatus You Need</i>.--For this experimental continuous wave
+      telegraph transmitter get the following pieces of apparatus: (1) one <i>single
+      coil tuner with three clips</i>; (2) one <i>.002 mfd. fixed condenser</i>;
+      (3) three <i>.001 mfd. condensers</i>; (4) one <i>adjustable grid leak</i>;
+      (5) one <i>hot-wire ammeter</i>; (6) one <i>buzzer</i>; (7) one <i>dry
+      cell</i>; (8) one <i>telegraph key</i>; (9) one <i>100 volt plate vacuum
+      tube amplifier</i>; (10) one <i>6 volt storage battery</i>; (11) one <i>rheostat</i>;
+      (12) one <i>oscillation choke coil</i>; (13) one <i>panel cut-out</i> with
+      a <i>single-throw, double-pole switch</i>, and a pair of <i>fuse sockets</i>
+      on it.
+    </p>
+    <p>
+      <i>The Tuning Coil</i>.--You can either make this tuning coil or buy one.
+      To make it get two disks of wood 3/4-inch thick and 5 inches in diameter
+      and four strips of hard wood, or better, hard rubber or composition
+      strips, such as <i>bakelite</i>, 1/2-inch thick, 1 inch wide and 5-3/4
+      inches long, and screw them to the disks as shown at <i>A</i> in <i>Fig.
+      75</i>. Now wrap on this form about 25 turns of No. 8 or 10, Brown and
+      Sharpe gauge, bare copper wire with a space of 1/8-inch between each turn.
+      Get three of the smallest size terminal clips, see <i>B</i>, and clip them
+      on to the different turns, when your tuning coil is ready for use. You can
+      buy a coil of this kind for $4.00 or $5.00.
+    </p>
+    <p>
+      <i>The Condensers</i>.--For the aerial series condenser get one that has a
+      capacitance of .002 mfd. and that will stand a potential of 3,000 volts.
+      [Footnote: The U C-1014 <i>Faradon</i> condenser made by the Radio
+      Corporation of America will serve the purpose.] It is shown at <i>C</i>.
+      The other three condensers, see <i>D</i>, are also of the fixed type and
+      may have a capacitance of .001 mfd.; [Footnote: List No. 266; fixed
+      receiving condenser, sold by the Manhattan Electrical Supply Co.] the
+      blocking condenser should preferably have a capacitance of 1/2 a mfd. In
+      these condensers the leaves of the sheet metal are embedded in
+      composition. The aerial condenser will cost you $2.00 and the others 75
+      cents each.
+    </p>
+    <p>
+      <a name="fig075a" id="fig075a"><img width="587" height="800"
+      src="images/fig075a.jpg"
+      alt="(A) Fig. 75.--Apparatus for Experimental C. W. Telegraph Transmitter." />
+      </a> <a name="fig075b" id="fig075b"><img width="600" height="526"
+      src="images/fig075b.jpg"
+      alt="Fig. 75.--Apparatus for Experimental C. W. Telegraph Transmitter." />
+      </a>
+    </p>
+    <p>
+      <i>The Aerial Ammeter.</i>--This instrument is also called a <i>hot-wire</i>
+      ammeter because the oscillating currents flowing through a piece of wire
+      heat it according to their current strength and as the wire contracts and
+      expands it moves a needle over a scale. The ammeter is connected in the
+      aerial wire system, either in the aerial side or the ground side--the
+      latter place is usually the most convenient. When you tune the transmitter
+      so that the ammeter shows the largest amount of current surging in the
+      aerial wire system you can consider that the oscillation circuits are in
+      tune. A hot-wire ammeter reading to 2.5 amperes will serve your needs, it
+      costs $6.00 and is shown at <i>E</i> in <i>Fig. 75</i>.
+    </p>
+    <table cellspacing="20" summary="Illustration">
+      <tr>
+        <td align="center">
+          <i>Photograph unavailable</i>
+        </td>
+      </tr>
+      <tr>
+        <td align="center">
+          United States Naval High Power Station, Arlington Va. General view of
+          Power Room. At the left can be seen the Control Switchboards, and
+          overhead, the great 30 K.W. Arc Transmitter with Accessories.
+        </td>
+      </tr>
+    </table>
+    <p>
+      <i>The Buzzer and Dry Cell</i>.--While a heterodyne, or beat, receptor can
+      receive continuous wave telegraph signals an ordinary crystal or vacuum
+      tube detector receiving set cannot receive them unless they are broken up
+      into trains either at the sending station or at the receiving station, and
+      it is considered the better practice to do this at the former rather than
+      at the latter station. For this small transmitter you can use an ordinary
+      buzzer as shown at <i>F</i>. A dry cell or two must be used to energize
+      the buzzer. You can get one for about 75 cents.
+    </p>
+    <p>
+      <i>The Telegraph Key</i>.--Any kind of a telegraph key will serve to break
+      up the trains of sustained oscillations into dots and dashes. The key
+      shown at <i>G</i> is mounted on a composition base and is the cheapest key
+      made, costing $1.50.
+    </p>
+    <p>
+      <i>The Vacuum Tube Oscillator</i>.--As explained before you can use any
+      amplifying tube that is made for a plate potential of 100 volts. The
+      current required for heating the filament is about 1 ampere at 6 volts. A
+      porcelain socket should be used for this tube as it is the best insulating
+      material for the purpose. An amplifier tube of this type is shown at <i>H</i>
+      and costs $6.50.
+    </p>
+    <p>
+      <i>The Storage Battery</i>.--A storage battery is used to heat the
+      filament of the tube, just as it is with a detector tube, and it can be of
+      any make or capacity as long as it will develop 6 volts. The cheapest 6
+      volt storage battery on the market has a 20 to 40 ampere-hour capacity and
+      sells for $13.00.
+    </p>
+    <p>
+      <i>The Battery Rheostat</i>.--As with the receptors a rheostat is needed
+      to regulate the current that heats the filament. A rheostat of this kind
+      is shown at <i>I</i> and is listed at $1.25.
+    </p>
+    <p>
+      <i>The Oscillation Choke Coil</i>.--This coil is connected in between the
+      oscillation circuits and the source of current which feeds the oscillator
+      tube to keep the oscillations set up by the latter from surging back into
+      the service wires where they would break down the insulation. You can make
+      an oscillation choke coil by winding say 100 turns of No. 28 Brown and
+      Sharpe gauge double cotton covered magnet wire on a cardboard cylinder 2
+      inches in diameter and 2-1/2 inches long.
+    </p>
+    <p>
+      <i>Transmitter Connectors</i>.--For connecting up the different pieces of
+      apparatus of the transmitter it is a good scheme to use <i>copper braid</i>;
+      this is made of braided copper wire in three sizes and sells for 7,15 and
+      20 cents a foot respectively. A piece of it is pictured at <i>J</i>.
+    </p>
+    <p>
+      <i>The Panel Cut-Out</i>.--This is used to connect the cord of the
+      110-volt lamp socket with the transmitter. It consists of a pair of <i>plug
+      cutouts and a single-throw, double-pole</i> switch mounted on a porcelain
+      base as shown at <i>K</i>. In some localities it is necessary to place
+      these in an iron box to conform to the requirements of the fire
+      underwriters.
+    </p>
+    <p>
+      <i>Connecting Up the Transmitting Apparatus</i>.--The way the various
+      pieces of apparatus are connected together is shown in the wiring diagram.
+      <i>Fig. 76</i>. Begin by connecting one post of the ammeter with the wire
+      that leads to the aerial and the other post of it to one end of the tuning
+      coil; connect clip <i>1</i> to one terminal of the .002 mfd. 3,000 volt
+      aerial condenser and the other post of this with the ground.
+    </p>
+    <p>
+      <a name="fig076" id="fig076"><img width="600" height="538"
+      src="images/fig076.jpg"
+      alt="Fig. 76--Experimental C.W. Telegraph Transmitter" /></a>
+    </p>
+    <p>
+      Now connect the end of the tuning coil that leads to the ammeter with one
+      end of the .001 mfd. grid condenser and the other end of this with the
+      grid of the vacuum tube. Connect the telegraph key, the buzzer and the dry
+      cell in series and then shunt them around the grid condenser. Next connect
+      the plate of the tube with one end of the .001 mfd. blocking condenser and
+      the other end of this with the clip <i>2</i> on the tuning coil.
+    </p>
+    <p>
+      Connect one end of the filament with the + or positive electrode of the
+      storage battery, the - or negative electrode of this with one post of the
+      rheostat and the other post of the latter with the other end of the
+      filament; then connect clip <i>3</i> with the + or positive side of the
+      storage battery. This done connect one end of the choke coil to the
+      conductor that leads to the plate and connect the other end of the choke
+      coil to one of the taps of the switch on the panel cut-out. Connect the +
+      or positive electrode of the storage battery to the other switch tap and
+      between the switch and the choke coil connect the protective condenser
+      across the 110 volt feed wires. Finally connect the lamp cord from the
+      socket to the plug fuse taps when your experimental continuous wave
+      telegraph transmitter is ready to use.
+    </p>
+    <p>
+      <i>A 100 Mile C. W. Telegraph Transmitter</i>.--Here is a continuous wave
+      telegraph transmitter that will cover distances up to 100 miles that you
+      can rely on. It is built on exactly the same lines as the experimental
+      transmitter just described, but instead of using a 100 volt plate
+      amplifier as a makeshift generator of oscillations it employs a vacuum
+      tube made especially for setting up oscillations and instead of having a
+      low plate voltage it is energized with 350 volts.
+    </p>
+    <p>
+      <i>The Apparatus You Need</i>.--For this transmitter you require: (1) one
+      <i>oscillation transformer</i>; (2) one <i>hot-wire ammeter</i>; (3) one
+      <i>aerial series condenser</i>; (4) one <i>grid leak resistance</i>; (5)
+      one <i>chopper</i>; (6) one <i>key circuit choke coil</i>; (7) one <i>5
+      watt vacuum tube oscillator</i>; (8) one <i>6 volt storage battery</i>;
+      (9) one <i>battery rheostat</i>; (10) one <i>battery voltmeter</i>; (11)
+      one <i>blocking condenser</i>; (12) one <i>power circuit choke coil</i>,
+      and (13) one <i>motor-generator</i>.
+    </p>
+    <p>
+      <i>The Oscillation Transformer</i>.--The tuning coil, or <i>oscillation
+      transformer</i> as this one is called, is a conductively coupled
+      tuner--that is, the primary and secondary coils form one continuous coil
+      instead of two separate coils. This tuner is made up of 25 turns of thin
+      copper strip, 3/8 inch wide and with its edges rounded, and this is
+      secured to a wood base as shown at <i>A</i> in <i>Fig. 77</i>. It is
+      fitted with one fixed tap and three clips to each of which a length of
+      copper braid is attached. It has a diameter of 6-1/4 inches, a height of
+      7-7/8 inches and a length of 9-3/8 inches, and it costs $11.00.
+    </p>
+    <p>
+      <a name="fig077" id="fig077"><img width="548" height="800"
+      src="images/fig077.jpg"
+      alt="Fig. 77.--Apparatus of 100 Mile C. W. Telegraph Transmitter." /></a>
+    </p>
+    <p>
+      <i>The Aerial Condenser</i>.--This condenser is made up of three fixed
+      condensers of different capacitances, namely .0003, .0004 and .0005 mfd.,
+      and these are made to stand a potential of 7500 volts. The condenser is
+      therefore adjustable and, as you will see from the picture <i>B</i>, it
+      has one terminal wire at one end and three terminal wires at the other end
+      so that one, two or three condensers can be used in series with the
+      aerial. A condenser of this kind costs $5.40.
+    </p>
+    <p>
+      <i>The Aerial Ammeter</i>.--This is the same kind of a hot-wire ammeter
+      already described in connection with the experimental set, but it reads to
+      5 amperes.
+    </p>
+    <p>
+      <i>The Grid and Blocking Condensers</i>.--Each of these is a fixed
+      condenser of .002 mfd. capacitance and is rated to stand 3,000 volts. It
+      is made like the aerial condenser but has only two terminals. It costs
+      $2.00.
+    </p>
+    <p>
+      <i>The Key Circuit Apparatus</i>.--This consists of: (1) the <i>grid leak</i>;
+      (2) the <i>chopper</i>; (3) the <i>choke coil</i>, and (4) the <i>key</i>.
+      The grid leak is connected in the lead from the grid to the aerial to keep
+      the voltage on the grid at the right potential. It has a resistance of
+      5000 ohms with a mid-tap at 2500 ohms as shown at <i>C</i>. It costs
+      $2.00.
+    </p>
+    <p>
+      The chopper is simply a rotary interrupter driven by a small motor. It
+      comprises a wheel of insulating material in which 30 or more metal
+      segments are set in an insulating disk as shown at <i>D</i>. A metal
+      contact called a brush is fixed on either side of the wheel. It costs
+      about $7.00 and the motor to drive it is extra. The choke coil is wound up
+      of about 250 turns of No. 30 Brown and Sharpe gauge cotton covered magnet
+      wire on a spool which has a diameter of 2 inches and a length of 3-1/4
+      inches.
+    </p>
+    <p>
+      <i>The 5 Watt Oscillator Vacuum Tube</i>.--This tube is made like the
+      amplifier tube described for use with the preceding experimental
+      transmitter, but it is larger, has a more perfect vacuum, and will stand a
+      plate potential of 350 volts while the plate current is .045 ampere. The
+      filament takes a current of a little more than 2 amperes at 7.5 volts. A
+      standard 4-tap base is used with it. The tube costs $8.00 and the
+      porcelain base is $1.00 extra. It is shown at <i>E</i>.
+    </p>
+    <p>
+      <i>The Storage Battery and Rheostat</i>.--This must be a 5-cell battery so
+      that it will develop 10 volts. A storage battery of any capacity can be
+      used but the lowest priced one costs about $22.00. The rheostat for
+      regulating the battery current is the same as that used in the preceding
+      experimental transmitter.
+    </p>
+    <p>
+      <i>The Filament Voltmeter</i>.--To get the best results it is necessary
+      that the voltage of the current which heats the filament be kept at the
+      same value all of the time. For this transmitter a direct current
+      voltmeter reading from 0 to 15 volts is used. It is shown at <i>F</i> and
+      costs $7.50.
+    </p>
+    <p>
+      <i>The Oscillation Choke Coil</i>.--This is made exactly like the one
+      described in connection with the experimental transmitter.
+    </p>
+    <p>
+      <i>The Motor-Generator Set</i>.--Where you have only a 110 or a 220 volt
+      direct current available as a source of power you need a <i>motor-generator</i>
+      to change it to 350 volts, and this is an expensive piece of apparatus. It
+      consists of a single armature core with a motor winding and a generator
+      winding on it and each of these has its own commutator. Where the low
+      voltage current flows into one of the windings it drives its as a motor
+      and this in turn generates the higher voltage current in the other
+      winding. Get a 100 watt 350 volt motor-generator; it is shown at <i>F</i>
+      and costs about $75.00.
+    </p>
+    <p>
+      <i>The Panel Cut-Out</i>.--This switch and fuse block is the same as that
+      used in the experimental set.
+    </p>
+    <p>
+      <i>The Protective Condenser</i>.--This is a fixed condenser having a
+      capacitance of 1 mfd. and will stand 750 volts. It costs $2.00.
+    </p>
+    <p>
+      <i>Connecting Up the Transmitting Apparatus</i>.--From all that has gone
+      before you have seen that each piece of apparatus is fitted with terminal,
+      wires, taps or binding posts. To connect up the parts of this transmitter
+      it is only necessary to make the connections as shown in the wiring
+      diagram <i>Fig. 78</i>.
+    </p>
+    <p>
+      <a name="fig078" id="fig078"><img width="600" height="458"
+      src="images/fig078.jpg"
+      alt="Fig. 78.--5 to 50 Watt C. W. Telegraph Transmitter. (With Single Oscillation Tube.)" />
+      </a>
+    </p>
+    <p>
+      <i>A 200 Mile C. W. Telegraph Transmitter</i>.--To make a continuous wave
+      telegraph transmitter that will cover distances up to 200 miles all you
+      have to do is to use two 5 watt vacuum tubes in <i>parallel</i>, all of
+      the rest of the apparatus being exactly the same. Connecting the
+      oscillator tubes up in parallel means that the two filaments are connected
+      across the leads of the storage battery, the two grids on the same lead
+      that goes to the aerial and the two plates on the same lead that goes to
+      the positive pole of the generator. Where two or more oscillator tubes are
+      used only one storage battery is needed, but each filament must have its
+      own rheostat. The wiring diagram <i>Fig. 79</i> shows how the two tubes
+      are connected up in parallel.
+    </p>
+    <p>
+      <a name="fig079" id="fig079"><img width="600" height="367"
+      src="images/fig079.jpg"
+      alt="Fig. 79.--200 Mile C.W. Telegraph Transmitter (With Two Tubes in Parallel.)" />
+      </a>
+    </p>
+    <p>
+      <i>A 500 Mile C. W. Telegraph Transmitter</i>.--For sending to distances
+      of over 200 miles and up to 500 miles you can use either: (1) three or
+      four 5 watt oscillator tubes in parallel as described above, or (2) one 50
+      watt oscillator tube. Much of the apparatus for a 50 watt tube set is
+      exactly the same as that used for the 5 watt sets. Some of the parts,
+      however, must be proportionately larger though the design all the way
+      through remains the same.
+    </p>
+    <p>
+      <i>The Apparatus and Connections</i>.--The aerial series condenser, the
+      blocking condenser, the grid condenser, the telegraph key, the chopper,
+      the choke coil in the key circuit, the filament voltmeter and the
+      protective condenser in the power circuit are identical with those
+      described for the 5 watt transmitting set.
+    </p>
+    <p>
+      <i>The 50 Watt Vacuum Tube Oscillator</i>.--This is the size of tube
+      generally used by amateurs for long distance continuous wave telegraphy. A
+      single tube will develop 2 to 3 amperes in your aerial. The filament takes
+      a 10 volt current and a plate potential of 1,000 volts is needed. One of
+      these tubes is shown in <i>Fig. 80</i> and the cost is $30.00. A tube
+      socket to fit it costs $2.50 extra.
+    </p>
+    <p>
+      <a name="fig080" id="fig080"><img width="560" height="235"
+      src="images/fig080.jpg" alt="Fig. 80.--50 Watt Oscillator Vacuum Tube." /></a>
+    </p>
+    <p>
+      <i>The Aerial Ammeter</i>.--This should read to 5 amperes and the cost is
+      $6.25.
+    </p>
+    <p>
+      <i>The Grid Leak Resistance</i>.--It has the same resistance, namely 5,000
+      ohms as the one used with the 5 watt tube transmitter, but it is a little
+      larger. It is listed at $1.65.
+    </p>
+    <p>
+      <i>The Oscillation Choke Coil</i>.--The choke coil in the power circuit is
+      made of about 260 turns of No. 30 B. &amp; S. cotton covered magnet wire
+      wound on a spool 2-1/4 inches in diameter and 3-1/4 inches long.
+    </p>
+    <p>
+      <i>The Filament Rheostat</i>.--This is made to take care of a 10 volt
+      current and it costs $10.00.
+    </p>
+    <p>
+      <i>The Filament Storage Battery</i>.--This must develop 12 volts and one
+      having an output of 40 ampere-hours costs about $25.00.
+    </p>
+    <p>
+      <i>The Protective Condenser</i>.--This condenser has a capacitance of 1
+      mfd. and costs $2.00.
+    </p>
+    <p>
+      <i>The Motor-Generator</i>.--Where you use one 50 watt oscillator tube you
+      will need a motor-generator that develops a plate potential of 1000 volts
+      and has an output of 200 watts. This machine will stand you about $100.00.
+    </p>
+    <p>
+      The different pieces of apparatus for this set are connected up exactly
+      the same as shown in the wiring diagram in <i>Fig. 78</i>.
+    </p>
+    <p>
+      <i>A 1000 Mile C. W. Telegraph Transmitter</i>.--All of the parts of this
+      transmitting set are the same as for the 500 mile transmitter just
+      described except the motor generator and while this develops the same
+      plate potential, <i>i.e.</i>, 1,000 volts, it must have an output of 500
+      watts; it will cost you in the neighborhood of $175.00. For this long
+      distance transmitter you use two 50 watt oscillator tubes in parallel and
+      all of the parts are connected together exactly the same as for the 200
+      mile transmitter shown in the wiring diagram in <i>Fig. 79</i>.
+    </p>
+    <h2>
+      <a name="chap17" id="chap17">CHAPTER XVII</a>
+    </h2>
+    <h3>
+      CONTINUOUS WAVE TELEGRAPH TRANSMITTING SETS WITH ALTERNATING CURRENT
+    </h3>
+    <p>
+      Within the last few years alternating current has largely taken the place
+      of direct current for light, heat and power purposes in and around towns
+      and cities and if you have alternating current service in your home you
+      can install a long distance continuous wave telegraph transmitter with
+      very little trouble and at a comparatively small expense.
+    </p>
+    <p>
+      <i>A 100 Mile C. W. Telegraph Transmitting Set</i>.--The principal pieces
+      of apparatus for this transmitter are the same as those used for the <i>100
+      Mile Continuous Wave Telegraph Transmitting Set</i> described and pictured
+      in the preceding chapter which used direct current, except that an <i>alternating
+      current power transformer</i> is employed instead of the more costly <i>motor-generator</i>.
+    </p>
+    <p>
+      <i>The Apparatus Required</i>.--The various pieces of apparatus you will
+      need for this transmitting set are: (1) one <i>hot-wire ammeter</i> for
+      the aerial as shown at <i>E</i> in <i>Fig. 75</i>, but which reads to 5
+      amperes instead of to 2.5 amperes; (2) one <i>tuning coil</i> as shown at
+      <i>A</i> in <i>Fig. 77</i>; (3) one aerial condenser as shown at <i>B</i>
+      in <i>Fig. 77</i>; (4) one <i>grid leak</i> as shown at <i>C</i> in <i>Fig.
+      77</i>; (5) one <i>telegraph key</i> as shown at <i>G</i> in <i>Fig. 75</i>;
+      (6) one <i>grid condenser</i>, made like the aerial condenser but having
+      only two terminals; (7) one <i>5 watt oscillator tube</i> as shown at <i>E</i>
+      in <i>Fig. 77</i>; (8) one <i>.002 mfd. 3,000 volt by-pass condenser</i>,
+      made like the aerial and grid condensers; (9) one pair of <i>choke coils</i>
+      for the high voltage secondary circuit; (10) one <i>milli-ammeter</i>;
+      (11) one A. C. <i>power transformer</i>; (12) one <i>rheostat</i> as shown
+      at <i>I</i> in <i>Fig. 75</i>, and (13) one <i>panel cut-out</i> as shown
+      at <i>K</i> in <i>Fig. 75</i>.
+    </p>
+    <p>
+      <i>The Choke Coils</i>.--Each of these is made by winding about 100 turns
+      of No. 28, Brown and Sharpe gauge, cotton covered magnet wire on a spool 2
+      inches in diameter and 2-1/2 inches long, when it will have an inductance
+      of about 0.5 <i>millihenry</i> [Footnote: A millihenry is 1/1000th part of
+      a henry.] at 1,000 cycles.
+    </p>
+    <p>
+      <i>The Milli-ammeter</i>.--This is an alternating current ammeter and
+      reads from 0 to 250 <i>milli</i>amperes; [Footnote: A <i>milliampere</i>
+      is the 1/1000th part of an ampere.] and is used for measuring the
+      secondary current that energizes the plate of the oscillator tube. It
+      looks like the aerial ammeter and costs about $7.50.
+    </p>
+    <p>
+      <i>The A. C. Power Transformer</i>.--Differing from the motor generator
+      set the power transformer has no moving parts. For this transmitting set
+      you need a transformer that has an input of 325 volts. It is made to work
+      on a 50 to 60 cycle current at 102.5 to 115 volts, which is the range of
+      voltage of the ordinary alternating lighting current. This adjustment for
+      voltage is made by means of taps brought out from the primary coil to a
+      rotary switch.
+    </p>
+    <p>
+      The high voltage secondary coil which energizes the plate has an output of
+      175 watts and develops a potential of from 350 to 1,100 volts. The low
+      voltage secondary coil which heats the filament has an output of 175 watts
+      and develops 7.5 volts. This transformer, which is shown in <i>Fig. 81</i>,
+      is large enough to take care of from one to four 5 watt oscillator tubes.
+      It weighs about 15 pounds and sells for $25.00.
+    </p>
+    <p>
+      <a name="fig081" id="fig081"><img width="600" height="661"
+      src="images/fig081.jpg"
+      alt="Fig. 81.--Alternation Current Power Transformer. (For C. W. Telegraphy and Wireless Telephony.)" />
+      </a>
+    </p>
+    <table cellspacing="20" summary="Illustration">
+      <tr>
+        <td align="center">
+          <i>Photograph unavailable</i>
+        </td>
+      </tr>
+      <tr>
+        <td align="center">
+          The Transformer and Tuner of the World's Largest Radio Station. Owned
+          by the Radio Corporation of America at Rocky Point near Port Jefferson
+          L.I.
+        </td>
+      </tr>
+    </table>
+    <p>
+      <i>Connecting Up the Apparatus</i>.--The wiring diagram <i>Fig. 82</i>
+      shows clearly how all of the connections are made. It will be observed
+      that a storage battery is not needed as the secondary coil of the
+      transformer supplies the current to heat the filament of the oscillator.
+      The filament voltmeter is connected across the filament secondary coil
+      terminals, while the plate milli-ammeter is connected to the mid-taps of
+      the plate secondary coil and the filament secondary coil.
+    </p>
+    <p>
+      <a name="fig082" id="fig082"><img width="600" height="337"
+      src="images/fig082.jpg"
+      alt="Fig. 82. Wiring Diagram for 200 to 500 Mile C.W. Telegraph Transmitting Set. (With Alternating Current)" />
+      </a>
+    </p>
+    <p>
+      <i>A 200 to 500 Mile C. W. Telegraph Transmitting Set</i>.--Distances of
+      from 200 to 500 miles can be successfully covered with a telegraph
+      transmitter using two, three or four 5 watt oscillator tubes in parallel.
+      The apparatus needed is identical with that used for the 100 mile
+      transmitter just described. The tubes are connected in parallel as shown
+      in the wiring diagram in <i>Fig. 83</i>.
+    </p>
+    <p>
+      <a name="fig083" id="fig083"><img width="600" height="306"
+      src="images/fig083.jpg"
+      alt="Fig. 83.--Wiring Diagram for 500 to 1000 Mile C. W. Telegraph Transmitter." />
+      </a>
+    </p>
+    <p>
+      <i>A 500 to 1,000 Mile C. W. Telegraph Transmitting Set</i>.--With the
+      apparatus described for the above set and a single 50 watt oscillator tube
+      a distance of upwards of 500 miles can be covered, while with two 50 watt
+      oscillator tubes in parallel you can cover a distance of 1,000 miles
+      without difficulty, and nearly 2,000 miles have been covered with this
+      set.
+    </p>
+    <p>
+      <i>The Apparatus Required</i>.--All of the apparatus for this C. W.
+      telegraph transmitting set is the same as that described for the 100 and
+      200 mile sets but you will need: (1) one or two <i>50 watt oscillator
+      tubes with sockets;</i> (2) one <i>key</i> <i>condenser</i> that has a
+      capacitance of 1 mfd., and a rated potential of 1,750 volts; (3) one <i>0
+      to 500 milli-ammeter</i>; (4) one <i>aerial ammeter</i> reading to 5
+      amperes, and (5) an <i>A. C. power transformer</i> for one or two 50 watt
+      tubes.
+    </p>
+    <table cellspacing="20" summary="Illustration">
+      <tr>
+        <td align="center">
+          <i>Photograph unavailable</i>
+        </td>
+      </tr>
+      <tr>
+        <td align="center">
+          Broadcasting Government Reports by Wireless from Washington. This
+          shows Mr. Gale at work with his set in the Post Office Department.
+        </td>
+      </tr>
+    </table>
+    <p>
+      <i>The Alternating Current Power Transformer</i>.--This power transformer
+      is made exactly like the one described in connection with the preceding
+      100 mile transmitter and pictured in <i>Fig. 81</i>, but it is
+      considerably larger. Like the smaller one, however, it is made to work
+      with a 50 to 60 cycle current at 102.5 to 115 volts and, hence, can be
+      used with any A. C. lighting current.
+    </p>
+    <p>
+      It has an input of 750 volts and the high voltage secondary coil which
+      energizes the plate has an output of 450 watts and develops 1,500 to 3,000
+      volts. The low voltage secondary coil which heats the filament develops
+      10.5 volts. This transformer will supply current for one or two 50-watt
+      oscillator tubes and it costs about $40.00.
+    </p>
+    <p>
+      <i>Connecting Up the Apparatus</i>.--Where a single oscillator tube is
+      used the parts are connected as shown in <i>Fig. 82</i>, and where two
+      tubes are connected in parallel the various pieces of apparatus are wired
+      together as shown in <i>Fig. 83</i>. The only difference between the 5
+      watt tube transmitter and the 50 watt tube transmitter is in the size of
+      the apparatus with one exception; where one or two 50 watt tubes are used
+      a second condenser of large capacitance (1 mfd.) is placed in the grid
+      circuit and the telegraph key is shunted around it as shown in the diagram
+      <i>Fig. 83</i>.
+    </p>
+    <h2>
+      <a name="chap18" id="chap18">CHAPTER XVIII</a>
+    </h2>
+    <h3>
+      WIRELESS TELEPHONE TRANSMITTING SETS WITH DIRECT AND ALTERNATING CURRENTS
+    </h3>
+    <p>
+      In time past the most difficult of all electrical apparatus for the
+      amateur to make, install and work was the wireless telephone. This was
+      because it required a <i>direct current</i> of not less than 500 volts to
+      set up the sustained oscillations and all ordinary direct current for
+      lighting purposes is usually generated at a potential of 110 volts.
+    </p>
+    <p>
+      Now as you know it is easy to <i>step-up</i> a 110 volt alternating
+      current to any voltage you wish with a power transformer but until within
+      comparatively recent years an alternating current could not be used for
+      the production of sustained oscillations for the very good reason that the
+      state of the art had not advanced that far. In the new order of things
+      these difficulties have all but vanished and while a wireless telephone
+      transmitter still requires a high voltage direct current to operate it
+      this is easily obtained from 110 volt source of alternating current by
+      means of <i>vacuum tube rectifiers</i>.
+    </p>
+    <p>
+      The pulsating direct currents are then passed through a filtering
+      reactance coil, called a <i>reactor</i>, and one or more condensers, and
+      these smooth them out until they approximate a continuous direct current.
+      The latter is then made to flow through a vacuum tube oscillator when it
+      is converted into high frequency oscillations and these are <i>varied</i>,
+      or <i>modulated</i>, as it is called, by a <i>microphone transmitter</i>
+      such as is used for ordinary wire telephony. The energy of these sustained
+      modulated oscillations is then radiated into space from the aerial in the
+      form of electric waves.
+    </p>
+    <p>
+      The distance that can be covered with a wireless telephone transmitter is
+      about one-fourth as great as that of a wireless telegraph transmitter
+      having the same input of initial current, but it is long enough to satisfy
+      the most enthusiastic amateur. For instance with a wireless telephone
+      transmitter where an amplifier tube is used to set up the oscillations and
+      which is made for a plate potential of 100 volts, distances up to 10 or 15
+      miles can be covered.
+    </p>
+    <p>
+      With a single 5 watt oscillator tube energized by a direct current of 350
+      volts from either a motor-generator or from a power transformer (after it
+      has been rectified and smoothed out) speech and music can be transmitted
+      to upwards of 25 miles. Where two 5 watt tubes connected in parallel are
+      used wireless telephone messages can be transmitted to distances of 40 or
+      50 miles. Further, a single 50 watt oscillator tube will send to distances
+      of 50 to 100 miles while two of these tubes in parallel will send from 100
+      to 200 miles. Finally, where four or five oscillator tubes are connected
+      in parallel proportionately greater distances can be covered.
+    </p>
+    <p>
+      <i>A Short Distance Wireless Telephone Transmitting Set-With 110 Volt
+      Direct Lighting Current</i>.--For this very simple, short distance
+      wireless telephone transmitting set you need the same apparatus as that
+      described and pictured in the beginning of <a href="#chap16">Chapter XVI</a>
+      for a <i>Short Distance C. W. Telegraph Transmitter</i>, except that you
+      use a <i>microphone transmitter</i> instead of a <i>telegraph key</i>. If
+      you have a 110 volt direct lighting current in your home you can put up
+      this short distance set for very little money and it will be well worth
+      your while to do so.
+    </p>
+    <p>
+      <i>The Apparatus You Need</i>.--For this set you require: (1) one <i>tuning
+      coil</i> as shown at <i>A</i> and <i>B</i> in <i>Fig. 75</i>; (2) one <i>aerial
+      ammeter</i> as shown at <i>C</i> in <i>Fig. 75</i>; (3) one <i>aerial
+      condenser</i> as shown at <i>C</i> in <i>Fig. 75</i>; (4) one <i>grid,
+      blocking and protective condenser</i> as shown at <i>D</i> in <i>Fig. 75</i>;
+      (5) one <i>grid leak</i> as shown at <i>C</i> in <i>Fig. 77</i>; (6) one
+      <i>vacuum tube amplifier</i> which is used as an <i>oscillator</i>; (7)
+      one <i>6 volt storage battery</i>; (8) one <i>rheostat</i> as shown at <i>I</i>
+      in <i>Fig. 75</i>; (9) one <i>oscillation choke coil</i>; (10) one <i>panel
+      cut-out</i> as shown at <i>K</i> in <i>Fig. 75</i> and an ordinary <i>microphone
+      transmitter</i>.
+    </p>
+    <p>
+      The <i>Microphone Transmitter</i>.--The best kind of a microphone to use
+      with this and other telephone transmitting sets is a <i>Western Electric
+      No. 284-W</i>. [Footnote: Made by the Western Electric Company, Chicago,
+      Ill.] This is known as a solid back transmitter and is the standard
+      commercial type used on all long distance Bell telephone lines. It
+      articulates sharply and distinctly and there are no current variations to
+      distort the wave form of the voice and it will not buzz or sizzle. It is
+      shown in <i>Fig. 84</i> and costs $2.00. Any other good microphone
+      transmitter can be used if desired.
+    </p>
+    <p>
+      <a name="fig084" id="fig084"><img width="600" height="365"
+      src="images/fig084.jpg" alt="Fig. 84.--Standard Microphone Transmitter." /></a>
+    </p>
+    <p>
+      <i>Connecting Up the Apparatus</i>.--Begin by connecting the leading-in
+      wire with one of the terminals of the microphone transmitter, as shown in
+      the wiring diagram <i>Fig. 85</i>, and the other terminal of this to one
+      end of the tuning coil. Now connect <i>clip 1</i> of the tuning coil to
+      one of the posts of the hot-wire ammeter, the other post of this to one
+      end of aerial condenser and, finally, the other end of the latter with the
+      water pipe or other ground. The microphone can be connected in the ground
+      wire and the ammeter in the aerial wire and the results will be
+      practically the same.
+    </p>
+    <p>
+      <a name="fig085" id="fig085"><img width="600" height="526"
+      src="images/fig085.jpg"
+      alt="Fig. 85.--Wiring Diagram of Short Distance Wireless Telephone Set. (Microphone in Aerial Wire.)" />
+      </a>
+    </p>
+    <p>
+      Next connect one end of the grid condenser to the post of the tuning coil
+      that makes connection with the microphone and the other end to the grid of
+      the tube, and then shunt the grid leak around the condenser. Connect the +
+      or <i>positive</i> electrode of the storage battery with one terminal of
+      the filament of the vacuum tube, the other terminal of the filament with
+      one post of the rheostat and the other post of this with the - or <i>negative</i>
+      electrode of the battery. This done, connect <i>clip 2</i> of the tuning
+      coil to the + or <i>positive</i> electrode of the battery and bring a lead
+      from it to one of the switch taps of the panel cut-out.
+    </p>
+    <p>
+      Now connect <i>clip 3</i> of the tuning coil with one end of the blocking
+      condenser, the other end of this with one terminal of the choke coil and
+      the other terminal of the latter with the other switch tap of the cut-out.
+      Connect the protective condenser across the direct current feed wires
+      between the panel cut-out and the choke coil. Finally connect the ends of
+      a lamp cord to the fuse socket taps of the cut-out, and connect the other
+      ends to a lamp plug and screw it into the lamp socket of the feed wires.
+      Screw in a pair of 5 ampere <i>fuse plugs</i>, close the switch and you
+      are ready to tune the transmitter and talk to your friends.
+    </p>
+    <p>
+      <i>A 25 to 50 Mile Wireless Telephone Transmitter--With Direct Current
+      Motor Generator</i>.--Where you have to start with 110 or 220 volt direct
+      current and you want to transmit to a distance of 25 miles or more you
+      will have to install a <i>motor-generator</i>. To make this transmitter
+      you will need exactly the same apparatus as that described and pictured
+      for the <i>100 Mile C. W. Telegraph Transmitting Set</i> in <a
+      href="#chap16">Chapter XVI</a>, except that you must substitute a <i>microphone
+      transmitter</i> and a <i>telephone induction coil</i>, or a <i>microphone
+      transformer</i>, or still better, a <i>magnetic modulator</i>, for the
+      telegraph key and chopper.
+    </p>
+    <p>
+      <i>The Apparatus You Need</i>.--To reiterate; the pieces of apparatus you
+      need are: (1) one <i>aerial ammeter</i> as shown at <i>E</i> in <i>Fig. 75</i>;
+      (2) one <i>tuning coil</i> as shown at <i>A</i> in <i>Fig. 77</i>; (3) one
+      <i>aerial condenser</i> as shown at <i>B</i> in <i>Fig. 77</i>; (4) one <i>grid
+      leak</i> as shown at <i>C</i> in <i>Fig. 77</i>; (5) one <i>grid, blocking</i>
+      and <i>protective condenser</i>; (6) one <i>5 watt oscillator tube</i> as
+      shown at <i>E</i> in <i>Fig. 77</i>; (7) one <i>rheostat</i> as shown at
+      <i>I</i> in <i>Fig. 75</i>; (8) one <i>10 volt (5 cell) storage battery</i>;
+      (9) one <i>choke coil</i>; (10) one <i>panel cut-out</i> as shown at <i>K</i>
+      in <i>Fig. 75</i>, and (11) a <i>motor-generator</i> having an input of
+      110 or 220 volts and an output of 350 volts.
+    </p>
+    <p>
+      In addition to the above apparatus you will need: (12) a <i>microphone
+      transmitter</i> as shown in <i>Fig. 84</i>; (13) a battery of four dry
+      cells or a 6 volt storage battery, and either (14) a <i>telephone
+      induction coil</i> as shown in <i>Fig. 86</i>; (15) a <i>microphone
+      transformer</i> as shown in <i>Fig. 87</i>; or a <i>magnetic modulator</i>
+      as shown in <i>Fig. 88</i>. All of these parts have been described, as
+      said above, in <a href="#chap16">Chapter XVI</a>, except the microphone
+      modulators.
+    </p>
+    <p>
+      <a name="fig086" id="fig086"><img width="600" height="508"
+      src="images/fig086.jpg"
+      alt="Fig. 86.--Telephone Induction Coil. (Used with Microphone Transmitter.)" />
+      </a> <a name="fig087" id="fig087"><img width="600" height="712"
+      src="images/fig087.jpg"
+      alt="Fig. 87.--Microphone Transformer. (Used with Microphone Transmitter.)" />
+      </a> <a name="fig088" id="fig088"><img width="600" height="692"
+      src="images/fig088.jpg"
+      alt="Fig. 88.--Magnetic Modulator. (Used with Microphone Transmitter.)" />
+      </a>
+    </p>
+    <p>
+      <i>The Telephone Induction Coil</i>.--This is a little induction coil that
+      transforms the 6-volt battery current after it has flowed through and been
+      modulated by the microphone transmitter into alternating currents that
+      have a potential of 1,000 volts of more. It consists of a primary coil of
+      <i>No. 20 B. and S.</i> gauge cotton covered magnet wire wound on a core
+      of soft iron wires while around the primary coil is wound a secondary coil
+      of <i>No. 30</i> magnet wire. Get a <i>standard telephone induction coil</i>
+      that has a resistance of 500 or 750 ohms and this will cost you a couple
+      of dollars.
+    </p>
+    <p>
+      <i>The Microphone Transformer</i>.--This device is built on exactly the
+      same principle as the telephone induction coil just described but it is
+      more effective because it is designed especially for modulating the
+      oscillations set up by vacuum tube transmitters. As with the telephone
+      induction coil, the microphone transmitter is connected in series with the
+      primary coil and a 6 volt dry or storage battery.
+    </p>
+    <p>
+      In the better makes of microphone transformer, there is a third winding,
+      called a <i>side tone</i> coil, to which a headphone can be connected so
+      that the operator who is speaking into the microphone can listen-in and so
+      learn if his transmitter is working up to standard.
+    </p>
+    <p>
+      <i>The Magnetic Modulator</i>.--This is a small closed iron core
+      transformer of peculiar design and having a primary and a secondary coil
+      wound on it. This device is used to control the variations of the
+      oscillating currents that are set up by the oscillator tube. It is made in
+      three sizes and for the transmitter here described you want the smallest
+      size, which has an output of 1/2 to 1-1/2 amperes. It costs about $10.00.
+    </p>
+    <p>
+      <i>How the Apparatus Is Connected Up</i>.--The different pieces of
+      apparatus are connected together in exactly the same way as the <i>100
+      Mile C. W. Telegraph Set</i> in <a href="#chap16">Chapter XVI</a> except
+      that the microphone transmitter and microphone modulator (whichever kind
+      you use) is substituted for the telegraph key and chopper.
+    </p>
+    <p>
+      Now there are three different ways that the microphone and its modulator
+      can be connected in circuit. Two of the best ways are shown at <i>A</i>
+      and <i>B</i> in <i>Fig. 89</i>. In the first way the secondary terminals
+      of the modulator are shunted around the grid leak in the grid circuit as
+      at <i>A</i>, and in the second the secondary terminals are connected in
+      the aerial as at <i>B</i>. Where an induction coil or a microphone
+      transformer is used they are shunted around a condenser, but this is not
+      necessary with the magnetic modulator. Where a second tube is used as in
+      <i>Fig. 90</i> then the microphone and its modulator are connected with
+      the grid circuit and <i>clip 3</i> of the tuning coil.
+    </p>
+    <p>
+      <a name="fig089a" id="fig089a"><img width="600" height="432"
+      src="images/fig089a.jpg"
+      alt="Fig. 89.--Wiring Diagram of 25 to 50 Mile Wireless Telephone. (Microphone Modulator Shunted Around Grid-Leak Condenser.)" />
+      </a> <a name="fig089b" id="fig089b"><img width="560" height="705"
+      src="images/fig089b.jpg"
+      alt="(B) Fig. 89.--Microphone Modulator Connected in Aerial Wire." /> </a>
+      <a name="fig090" id="fig090"><img width="600" height="379"
+      src="images/fig090.jpg"
+      alt="Fig. 90.--Wiring Diagram of 50 to 100 Mile Wireless Telephone Transmitting Set." />
+      </a>
+    </p>
+    <p>
+      <i>A 50 to 100 Mile Wireless Telephone Transmitter--With Direct Current
+      Motor Generator</i>.--As the initial source of current available is taken
+      to be a 110 or 220 volt direct current a motor-generator having an output
+      of 350 volts must be used as before. The only difference between this
+      transmitter and the preceding one is that: (1) two 5 watt tubes are used,
+      the first serving as an <i>oscillator</i> and the second as a <i>modulator</i>;
+      (2) an <i>oscillation choke coil</i> is used in the plate circuit; (3) a
+      <i>reactance coil</i> or <i>reactor</i>, is used in the plate circuit; and
+      (4) a <i>reactor</i> is used in the grid circuit.
+    </p>
+    <p>
+      <i>The Oscillation Choke Coil</i>.--You can make this choke coil by
+      winding about 275 turns of <i>No. 28 B. and S. gauge</i> cotton covered
+      magnet wire on a spool 2 inches in diameter and 4 inches long. Give it a
+      good coat of shellac varnish and let it dry thoroughly.
+    </p>
+    <p>
+      <i>The Plate and Grid Circuit Reactance Coils</i>.--Where a single tube is
+      used as an oscillator and a second tube is employed as a modulator, a <i>reactor</i>,
+      which is a coil of wire wound on an iron core, is used in the plate
+      circuit to keep the high voltage direct current of the motor-generator the
+      same at all times. Likewise the grid circuit reactor is used to keep the
+      voltage of the grid at a constant value. These reactors are made alike and
+      a picture of one of them is shown in <i>Fig. 91</i> and each one will cost
+      you $5.75.
+    </p>
+    <p>
+      <a name="fig091" id="fig091"><img width="511" height="680"
+      src="images/fig091.jpg" alt="Fig. 91.--Plate and Grid Circuit Reactor." /></a>
+    </p>
+    <p>
+      <i>Connecting up the Apparatus</i>.--All of the different pieces of
+      apparatus are connected up as shown in <i>Fig. 89</i>. One of the ends of
+      the secondary of the induction coil, or the microphone transformer, or the
+      magnetic modulator is connected to the grid circuit and the other end to
+      <i>clip 3</i> of the tuning coil.
+    </p>
+    <p>
+      <i>A 100 to 200 Mile Wireless Telephone Transmitter--With Direct Current
+      Motor Generator</i>.--By using the same connections shown in the wiring
+      diagrams in <i>Fig. 89</i> and a single 50 watt oscillator tube your
+      transmitter will then have a range of 100 miles or so, while if you
+      connect up the apparatus as shown in <i>Fig. 90</i> and use two 50 watt
+      tubes you can work up to 200 miles. Much of the apparatus for a 50 watt
+      oscillator set where either one or two tubes are used is of the same size
+      and design as that just described for the 5 watt oscillator sets, but, as
+      in the C. W. telegraph sets, some of the parts must be proportionately
+      larger. The required parts are (1) the <i>50 watt tube</i>; (2) the <i>grid
+      leak resistance</i>; (3) the <i>filament rheostat</i>; (4) the <i>filament
+      storage battery</i>; and (5) the <i>magnetic modulator</i>. All of these
+      parts, except the latter, are described in detail under the heading of a
+      <i>500 Mile C. W. Telegraph Transmitting Set</i> in <a href="#chap16">Chapter
+      XVI</a>, and are also pictured in that chapter.
+    </p>
+    <p>
+      It is not advisable to use an induction coil for the modulator for this
+      set, but use, instead, either a telephone transformer, or better, a
+      magnetic modulator of the second size which has an output of from 1-1/2 to
+      3-1/2 amperes. The magnetic modulator is described and pictured in this
+      chapter.
+    </p>
+    <p>
+      <i>A 50 to 100 Mile Wireless Telephone Transmitting Set--With 110 Volt
+      Alternating Current</i>.--If you have a 110 volt [Footnote: Alternating
+      current for lighting purposes ranges from 102.5 volts to 115 volts, so we
+      take the median and call it 110 volts.] alternating current available you
+      can use it for the initial source of energy for your wireless telephone
+      transmitter. The chief difference between a wireless telephone
+      transmitting set that uses an alternating current and one that uses a
+      direct current is that: (1) a <i>power transformer</i> is used for
+      stepping up the voltage instead of a motor-generator, and (2) a <i>vacuum
+      tube rectifier</i> must be used to convert the alternating current into
+      direct current.
+    </p>
+    <p>
+      <i>The Apparatus You Need</i>.--For this telephone transmitting set you
+      need: (1) one <i>aerial ammeter</i>; (2) one <i>tuning coil</i>; (3) one
+      <i>telephone modulator</i>; (4) one <i>aerial series condenser</i>; (5)
+      one <i>4 cell dry battery</i> or a 6 volt storage battery; (6) one <i>microphone
+      transmitter</i>; (7) one <i>battery switch</i>; (8) one <i>grid condenser</i>;
+      (9) one <i>grid leak</i>; (10) two <i>5 watt oscillator tubes with sockets</i>;
+      (11) one <i>blocking condenser</i>; (12) one <i>oscillation choke coil</i>;
+      (13) two <i>filter condensers</i>; (14) one <i>filter reactance coil</i>;
+      (15) an <i>alternating current power transformer</i>, and (16) two <i>20
+      watt rectifier vacuum tubes</i>.
+    </p>
+    <p>
+      All of the above pieces of apparatus are the same as those described for
+      the <i>100 Mile C. W. Telegraph Transmitter in Chapter XVII</i>, except:
+      (a) the <i>microphone modulator</i>; (b) the <i>microphone transmitter</i>
+      and (c) the <i>dry</i> or <i>storage battery</i>, all of which are
+      described in this chapter; and the new parts which are: (d) the <i>rectifier
+      vacuum tubes</i>; (e) the <i>filter condensers</i>; and (f) the <i>filter
+      reactance coil</i>; further and finally, the power transformer has a <i>third</i>
+      secondary coil on it and it is this that feeds the alternating current to
+      the rectifier tubes, which in turn converts it into a pulsating direct
+      current.
+    </p>
+    <p>
+      <i>The Vacuum Tube Rectifier</i>.--This rectifier has two electrodes, that
+      is, it has a filament and a plate like the original vacuum tube detector,
+      The smallest size rectifier tube requires a plate potential of 550 volts
+      which is developed by one of the secondary coils of the power transformer.
+      The filament terminal takes a current of 7.5 volts and this is supplied by
+      another secondary coil of the transformer. This rectifier tube delivers a
+      direct current of 20 watts at 350 volts. It looks exactly like the 5 watt
+      oscillator tube which is pictured at <i>E</i> in <i>Fig. 77</i>. The price
+      is $7.50.
+    </p>
+    <p>
+      <i>The Filter Condensers</i>.--These condensers are used in connection
+      with the reactance coil to smooth out the pulsating direct current after
+      it has passed through the rectifier tube. They have a capacitance of 1
+      mfd. and will stand 750 volts. These condensers cost about $2.00 each.
+    </p>
+    <p>
+      <i>The Filter Reactance Coil</i>.--This reactor which is shown in <i>Fig.
+      92</i>, has about the same appearance as the power transformer but it is
+      somewhat smaller. It consists of a coil of wire wound on a soft iron core
+      and has a large inductance, hence the capacitance of the filter condensers
+      are proportionately smaller than where a small inductance is used which
+      has been the general practice. The size you require for this set has an
+      output of 160 milliamperes and it will supply current for one to four 5
+      watt oscillator tubes. This size of reactor costs $11.50.
+    </p>
+    <p>
+      <a name="fig092" id="fig092"><img width="560" height="714"
+      src="images/fig092.jpg"
+      alt="Fig. 92.--Filter Reactor for Smoothing out Rectified Currents." /></a>
+    </p>
+    <p>
+      <i>Connecting Up the Apparatus</i>.--The wiring diagram in <i>Fig. 93</i>
+      shows how the various pieces of apparatus for this telephone transmitter
+      are connected up. You will observe: (1) that the terminals of the power
+      transformer secondary coil which develops 10 volts are connected to the
+      filaments of the oscillator tubes; (2) that the terminals of the other
+      secondary coil which develops 10 volts are connected with the filaments of
+      the rectifier tubes; (3) that the terminals of the third secondary coil
+      which develops 550 volts are connected with the plates of the rectifier
+      tubes; (4) that the pair of filter condensers are connected in parallel
+      and these are connected to the mid-taps of the two filament secondary
+      coils; (5) that the reactance coil and the third filter condenser are
+      connected together in series and these are shunted across the filter
+      condensers, which are in parallel; and, finally, (6) a lead connects the
+      mid-tap of the 550-volt secondary coil of the power transformer with the
+      connection between the reactor and the third filter condenser.
+    </p>
+    <p>
+      <a name="fig093" id="fig093"><img width="600" height="330"
+      src="images/fig093.jpg"
+      alt="Fig 93.--100 to 200 Mile Wireless Telephone Transmitter." /></a>
+    </p>
+    <p>
+      <i>A 100 to 200 Mile Wireless Telephone Transmitting Set--With 110 Volt
+      Alternating Current</i>.--This telephone transmitter is built up of
+      exactly the same pieces of apparatus and connected up in precisely the
+      same way as the one just described and shown in <i>Fig. 93</i>.
+    </p>
+    <p>
+      <i>Apparatus Required</i>.--The only differences between this and the
+      preceding transmitter are: (1) the <i>magnetic modulator</i>, if you use
+      one, should have an output of 3-1/2 to 5 amperes; (2) you will need two <i>50
+      watt oscillator tubes with sockets</i>; (3) two <i>150 watt rectifier
+      tubes with sockets</i>; (4) an <i>aerial ammeter</i> that reads to <i>5
+      amperes</i>; (5) three <i>1 mfd. filter condensers</i> in parallel; (6) <i>two
+      filter condensers of 1 mfd. capacitance</i> that will stand <i>1750 volts</i>;
+      and (6) a <i>300 milliampere filter reactor</i>.
+    </p>
+    <p>
+      The apparatus is wired up as shown in <i>Fig. 93</i>.
+    </p>
+    <h2>
+      <a name="chap19" id="chap19">CHAPTER XIX</a>
+    </h2>
+    <h3>
+      THE OPERATION OF VACUUM TUBE TRANSMITTERS
+    </h3>
+    <p>
+      The three foregoing chapters explained in detail the design and
+      construction of (1) two kinds of C. W. telegraph transmitters, and (2) two
+      kinds of wireless telephone transmitters, the difference between them
+      being whether they used (<i>A</i>) a direct current, or (<i>B</i>) an
+      alternating current as the initial source of energy. Of course there are
+      other differences between those of like types as, for instance, the
+      apparatus and connections used (<i>a</i>) in the key circuits, and (<i>b</i>)
+      in the microphone circuits. But in all of the transmitters described of
+      whatever type or kind the same fundamental device is used for setting up
+      sustained oscillations and this is the <i>vacuum tube</i>.
+    </p>
+    <p>
+      <i>The Operation of the Vacuum Tube Oscillator</i>.--The operation of the
+      vacuum tube in producing sustained oscillations depends on (1) the action
+      of the tube as a valve in setting up the oscillations in the first place
+      and (2) the action of the grid in amplifying the oscillations thus set up,
+      both of which we explained in <a href="#chap14">Chapter XIV</a>. In that
+      chapter it was also pointed out that a very small change in the grid
+      potential causes a corresponding and larger change in the amount of
+      current flowing from the plate to the filament; and that if a vacuum tube
+      is used for the production of oscillations the initial source of current
+      must have a high voltage, in fact the higher the plate voltage the more
+      powerful will be the oscillations.
+    </p>
+    <p>
+      To understand how oscillations are set up by a vacuum tube when a direct
+      current is applied to it, take a look at the simple circuits shown in <i>Fig.
+      94</i>. Now when you close the switch the voltage from the battery charges
+      the condenser and keeps it charged until you open it again; the instant
+      you do this the condenser discharges through the circuit which includes it
+      and the inductance coil, and the discharge of a condenser is always
+      oscillatory.
+    </p>
+    <p>
+      <a name="fig094ab" id="fig094ab"><img width="600" height="392"
+      src="images/fig094ab.jpg"
+      alt="(A) and (B) Fig. 94. Operation of Vacuum Tube Oscillators." /></a>
+    </p>
+    <p>
+      Where an oscillator tube is included in the circuits as shown at <i>A</i>
+      and <i>B</i> in <i>Fig. 94</i>, the grid takes the place of the switch and
+      any slight change in the voltage of either the grid or the plate is
+      sufficient to start a train of oscillations going. As these oscillations
+      surge through the tube the positive parts of them flow from the plate to
+      the filament and these carry more of the direct current with them.
+    </p>
+    <p>
+      To make a tube set up powerful oscillations then, it is only necessary
+      that an oscillation circuit shall be provided which will feed part of the
+      oscillations set up by the tube back to the grid circuit and when this is
+      done the oscillations will keep on being amplified until the tube reaches
+      the limit of its output.
+    </p>
+    <p>
+      <a name="fig094c" id="fig094c"><img width="484" height="240"
+      src="images/fig094c.jpg"
+      alt="(C) Fig. 94.--How a Direct Current Sets up Oscillations." /></a>
+    </p>
+    <p>
+      <i>The Operation of C. W. Telegraph Transmitters With Direct
+      Current--Short Distance C. W. Transmitter</i>.--In the transmitter shown
+      in the wiring diagram in <i>Fig. 76</i> the positive part of the 110 volt
+      direct current is carried down from the lamp socket through one side of
+      the panel cut-out, thence through the choke coil and to the plate of the
+      oscillator tube, when the latter is charged to the positive sign. The
+      negative part of the 110 volt direct current then flows down the other
+      wire to the filament so that there is a difference of potential between
+      the plate and the filament of 110 volts. Now when the 6-volt battery
+      current is switched on the filament is heated to brilliancy, and the
+      electrons thrown off by it form a conducting path between it and the
+      plate; the 110 volt current then flows from the latter to the former.
+    </p>
+    <p>
+      Now follow the wiring from the plate over to the blocking condenser,
+      thence to <i>clip 3</i> of the tuning coil, through the turns of the
+      latter to <i>clip 2</i> and over to the filament and, when the latter is
+      heated, you have a <i>closed oscillation circuit</i>. The oscillations
+      surging in the latter set up other and like oscillations in the tuning
+      coil between the end of which is connected with the grid, the aerial and
+      the <i>clip 2</i>, and these surge through the circuit formed by this
+      portion of the coil, the grid condenser and the filament; this is the
+      amplifying circuit and it corresponds to the regenerative circuit of a
+      receiving set.
+    </p>
+    <p>
+      When oscillations are set up in it the grid is alternately charged to the
+      positive and negative signs. These reversals of voltage set up stronger
+      and ever stronger oscillations in the plate circuit as before explained.
+      Not only do the oscillations surge in the closed circuits but they run to
+      and fro on the aerial wire when their energy is radiated in the form of
+      electric waves. The oscillations are varied by means of the telegraph key
+      which is placed in the grid circuit as shown in <i>Fig. 76</i>.
+    </p>
+    <p>
+      <i>The Operation of the Key Circuit</i>.--The effect in a C. W.
+      transmitter when a telegraph key is connected in series with a buzzer and
+      a battery and these are shunted around the condenser in the grid circuit,
+      is to rapidly change the wave form of the sustained oscillations, and
+      hence, the length of the waves that are sent out. While no sound can be
+      heard in the headphones at the receiving station so long as the points of
+      the key are not in contact, when they are in contact the oscillations are
+      modulated and sounds are heard in the headphones that correspond to the
+      frequency of the buzzer in the key circuit.
+    </p>
+    <p>
+      <i>The Operation of C. W. Telegraph Transmitters with Direct Current</i>.--The
+      chief differences between the long distance sets which use a direct
+      current, i.e., those described in <a href="#chap16">Chapter XVI</a>, and
+      the short distance transmitting sets are that the former use: (1) a
+      motor-generator set for changing the low voltage direct current into high
+      voltage direct current, and (2) a chopper in the key circuit. The way the
+      motor-generator changes the low- into high-voltage current has been
+      explained in <a href="#chap16">Chapter XVI</a>.
+    </p>
+    <p>
+      The chopper interrupts the oscillations surging through the grid circuit
+      at a frequency that the ear can hear, that is to say, about 800 to 1,000
+      times per second. When the key is open, of course, the sustained
+      oscillations set up in the circuits will send out continuous waves but
+      when the key is closed these oscillations are broken up and then they send
+      out discontinuous waves. If a heterodyne receiving set, see <a
+      href="#chap15">Chapter XV</a>, is being used at the other end you can
+      dispense with the chopper and the key circuit needed is very much
+      simplified. The operation of key circuits of the latter kind will be
+      described presently.
+    </p>
+    <p>
+      <i>The Operation of C. W. Telegraph Transmitters with Alternating
+      Current--With a Single Oscillator Tube</i>.--Where an oscillator tube
+      telegraph transmitter is operated by a 110 volt alternating current as the
+      initial source of energy, a buzzer, chopper or other interruptor is not
+      needed in the key circuit. This is because oscillations are set up only
+      when the plate is energized with the positive part of the alternating
+      current and this produces an intermittent musical tone in the headphones.
+      Hence this kind of a sending set is called a <i>tone transmitter</i>.
+    </p>
+    <p>
+      Since oscillations are set up only by the positive part or voltage of an
+      alternating current it is clear that, as a matter of fact, this kind of a
+      transmitter does not send out continuous waves and therefore it is not a
+      C. W. transmitter. This is graphically shown by the curve of the wave form
+      of the alternating current and the oscillations that are set up by the
+      positive part of it in <i>Fig. 95</i>. Whenever the positive half of the
+      alternating current energizes the plate then oscillations are set up by
+      the tube and, conversely, when the negative half of the current charges
+      the plate no oscillations are produced.
+    </p>
+    <p>
+      <a name="fig095" id="fig095"><img width="592" height="240"
+      src="images/fig095.jpg"
+      alt="Fig. 95.--Positive Voltage only sets up Oscillations." /></a>
+    </p>
+    <p>
+      You will also observe that the oscillations set up by the positive part of
+      the current are not of constant amplitude but start at zero the instant
+      the positive part begins to energize the plate and they keep on increasing
+      in amplitude as the current rises in voltage until the latter reaches its
+      maximum; then as it gradually drops again to zero the oscillations
+      decrease proportionately in amplitude with it.
+    </p>
+    <p>
+      <i>Heating the Filament with Alternating Current</i>.--Where an
+      alternating current power transformer is used to develop the necessary
+      plate voltage a second secondary coil is generally provided for heating
+      the filament of the oscillation tube. This is better than a direct current
+      for it adds to the life of the filament. When you use an alternating
+      current to heat the filament keep it at the same voltage rather than at
+      the same amperage (current strength). To do this you need only to use a
+      voltmeter across the filament terminals instead of an ammeter in series
+      with it; then regulate the voltage of the filament with a rheostat.
+    </p>
+    <p>
+      <i>The Operation of C. W. Telegraph Transmitters with Alternating
+      Current--With Two Oscillator Tubes</i>.--By using two oscillator tubes and
+      connecting them up with the power transformer and oscillating circuits as
+      shown in the wiring diagram in <i>Fig. 83</i> the plates are positively
+      energized alternately with every reversal of the current and,
+      consequently, there is no time period between the ending of the
+      oscillations set up by one tube and the beginning of the oscillations set
+      up by the other tube. In other words these oscillations are sustained but
+      as in the case of those of a single tube, their amplitude rises and falls.
+      This kind of a set is called a <i>full wave rectification transmitter</i>.
+    </p>
+    <p>
+      The waves radiated by this transmitter can be received by either a crystal
+      detector or a plain vacuum-tube detector but the heterodyne receptor will
+      give you better results than either of the foregoing types.
+    </p>
+    <p>
+      <i>The Operation of Wireless Telephone Transmitters with Direct
+      Current--Short Distance Transmitter</i>.--The operation of this short
+      distance wireless telephone transmitter, a wiring diagram of which is
+      shown in <i>Fig. 85</i> is exactly the same as that of the <i>Direct
+      Current Short Distance C. W. Telegraph Transmitter</i> already explained
+      in this chapter. The only difference in the operation of these sets is the
+      substitution of the <i>microphone transmitter</i> for the telegraph key.
+    </p>
+    <p>
+      <i>The Microphone Transmitter</i>.--The microphone transmitter that is
+      used to vary, or modulate, the sustained oscillations set up by the
+      oscillator tube and circuits is shown in <i>Fig. 84</i>. By referring to
+      the diagram at <i>A</i> in this figure you will readily understand how it
+      operates. When you speak into the mouthpiece the <i>sound waves</i>, which
+      are waves in the air, impinge upon the diaphragm and these set it into
+      vibration--that is, they make it move to and fro.
+    </p>
+    <p>
+      When the diaphragm moves toward the back of the transmitter it forces the
+      carbon granules that are in the cup closer together; this lowers their
+      resistance and allows more current from the battery to flow through them;
+      when the pressure of the air waves is removed from the diaphragm it
+      springs back toward the mouth-piece and the carbon granules loosen up when
+      the resistance offered by them is increased and less current can flow
+      through them. Where the oscillation current in the aerial wire is small
+      the transmitter can be connected directly in series with the latter when
+      the former will surge through it. As you speak into the microphone
+      transmitter its resistance is varied and the current strength of the
+      oscillations is varied accordingly.
+    </p>
+    <p>
+      <i>The Operation of Wireless Telephone Transmitters with Direct
+      Current--Long Distance Transmitters</i>.--In the wireless telephone
+      transmitters for long distance work which were shown and described in the
+      preceding chapter a battery is used to energize the microphone
+      transmitter, and these two elements are connected in series with a <i>microphone
+      modulator</i>. This latter device may be either (1) a <i>telephone
+      induction coil</i>, (2) a <i>microphone transformer</i>, or (3) a <i>magnetic
+      modulator</i>; the first two of these devices step-up the voltage of the
+      battery current and the amplified voltage thus developed is impressed on
+      the oscillations that surge through the closed oscillation circuit or the
+      aerial wire system according to the place where you connect it. The third
+      device works on a different principle and this will be described a little
+      farther along.
+    </p>
+    <p>
+      <i>The Operation of Microphone Modulators--The Induction Coil</i>.--This
+      device is really a miniature transformer, see <i>A</i> in <i>Fig. 86</i>,
+      and its purpose is to change the 6 volt direct current that flows through
+      the microphone into 100 volts alternating current; in turn, this is
+      impressed on the oscillations that are surging in either (1) the grid
+      circuit as shown at <i>A</i> in <i>Fig. 89</i>, and in <i>Fig. 90</i>, (2)
+      the aerial wire system, as shown at <i>B</i> in <i>Fig. 89</i> and <i>Fig.
+      93</i>. When the current from the battery flows through the primary coil
+      it magnetizes the soft iron core and as the microphone varies the strength
+      of the current the high voltage alternating currents set up in the
+      secondary coil of the induction coil are likewise varied, when they are
+      impressed upon and modulate the oscillating currents.
+    </p>
+    <p>
+      <i>The Microphone Transformer</i>.--This is an induction coil that is
+      designed especially for wireless telephone modulation. The iron core of
+      this transformer is also of the open magnetic circuit type, see <i>A</i>
+      in <i>Fig. 87</i>, and the <i>ratio</i> of the turns [Footnote: See
+      Chapter VI] of the primary and the secondary coil is such that when the
+      secondary current is impressed upon either the grid circuit or the aerial
+      wire system it controls the oscillations flowing through it with the
+      greatest efficiency.
+    </p>
+    <p>
+      <i>The Magnetic Modulator</i>.--This piece of apparatus is also called a
+      <i>magnetic amplifier</i>. The iron core is formed of very thin plates, or
+      <i>laminations</i> as they are called, and this permits high-frequency
+      oscillations to surge in a coil wound on it. In this transformer, see <i>A</i>
+      in <i>Fig. 88</i>, the current flowing through the microphone varies the
+      magnetic permeability of the soft iron core by the magnetic saturation of
+      the latter. Since the microphone current is absolutely distinct from the
+      oscillating currents surging through the coil of the transformer a very
+      small direct current flowing through a coil on the latter will vary or
+      modulate very large oscillating currents surging through the former. It is
+      shown connected in the aerial wire system at <i>A</i> in <i>Fig. 88</i>,
+      and in <i>Fig. 93</i>.
+    </p>
+    <p>
+      <i>Operation of the Vacuum Tube as a Modulator</i>.--Where a microphone
+      modulator of the induction coil or microphone transformer type is
+      connected in the grid circuit or aerial wire system the modulation is not
+      very effective, but by using a second tube as a <i>modulator</i>, as shown
+      in <i>Fig. 90</i>, an efficient degree of modulation can be had. Now there
+      are two methods by which a vacuum tube can be used as a modulator and
+      these are: (1) by the <i>absorption</i> of the energy of the current set
+      up by the oscillator tube, and (2) by <i>varying</i> the direct current
+      that energizes the plate of the oscillator tube.
+    </p>
+    <p>
+      The first of these two methods is not used because it absorbs the energy
+      of the oscillating current produced by the tube and it is therefore
+      wasteful. The second method is an efficient one, as the direct current is
+      varied before it passes into the oscillator tube. This is sufficient
+      reason for describing only the second method. The voltage of the grid of
+      the modulator tube is varied by the secondary coil of the induction coil
+      or microphone transformer, above described. In this way the modulator tube
+      acts like a variable resistance but it amplifies the variations impressed
+      on the oscillations set up by the oscillator tube. As the magnetic
+      modulator does the same thing a vacuum tube used as a modulator is not
+      needed where the former is employed. For this reason a magnetic modulator
+      is the cheapest in the long run.
+    </p>
+    <p>
+      <i>The Operation of Wireless Telephone Transmitters with Alternating
+      Current</i>.--Where an initial alternating current is used for wireless
+      telephony, the current must be rectified first and then smoothed out
+      before passing into the oscillator tube to be converted into oscillations.
+      Further so that the oscillations will be sustained, two oscillator tubes
+      must be used, and, finally, in order that the oscillations may not vary in
+      amplitude the alternating current must be first changed into direct
+      current by a pair of rectifier vacuum tubes, as shown in <i>Fig. 93.</i>
+      When this is done the plates will be positively charged alternately with
+      every reversal of the current in which case there will be no break in the
+      continuity of the oscillations set up and therefore in the waves that are
+      sent out.
+    </p>
+    <p>
+      <i>The Operation of Rectifier Vacuum Tubes</i>.--The vacuum tube rectifier
+      is simply a two electrode vacuum tube. The way in which it changes a
+      commercial alternating current into pulsating direct current is the same
+      as that in which a two electrode vacuum tube detector changes an
+      oscillating current into pulsating direct currents and this has been
+      explained in detail under the heading of <i>The Operation of a Two
+      Electrode Vacuum Tube Detector</i> in <a href="#chap12">Chapter XII</a>.
+      In the <i>C. W. Telegraph Transmitting Sets</i> described in <a
+      href="#chap17">Chapter XVII</a>, the oscillator tubes act as rectifiers as
+      well as oscillators but for wireless telephony the alternating current
+      must be rectified first so that a continuous direct current will result.
+    </p>
+    <p>
+      <i>The Operation of Reactors and Condensers</i>.--A reactor is a single
+      coil of wire wound on an iron core, see <i>Fig. 90</i> and <i>A</i> in <i>Fig.
+      91</i>, and it should preferably have a large inductance. The reactor for
+      the plate and grid circuit of a wireless telephone transmitter where one
+      or more tubes are used as modulators as shown in the wiring diagram in <i>Fig.
+      90</i>, and the filter reactor shown in <i>Fig. 92</i>, operate in the
+      same way.
+    </p>
+    <p>
+      When an alternating current flows through a coil of wire the reversals of
+      the current set up a <i>counter electromotive force</i> in it which
+      opposes, that is <i>reacts</i>, on the current, and the <i>higher</i> the
+      frequency of the current the <i>greater</i> will be the <i>reactance</i>.
+      When the positive half of an alternating current is made to flow through a
+      large resistance the current is smoothed out but at the same time a large
+      amount of its energy is used up in producing heat.
+    </p>
+    <p>
+      But when the positive half of an alternating current is made to flow
+      through a large inductance it acts like a large resistance as before and
+      likewise smooths out the current, but none of its energy is wasted in heat
+      and so a coil having a large inductance, which is called an <i>inductive
+      reactance</i>, or just <i>reactor</i> for short, is used to smooth out, or
+      filter, the alternating current after it has been changed into a pulsating
+      direct current by the rectifier tubes.
+    </p>
+    <p>
+      A condenser also has a reactance effect on an alternating current but
+      different from an induction coil the <i>lower</i> the frequency the <i>greater</i>
+      will be the reactance. For this reason both a filter reactor and <i>filter
+      condensers</i> are used to smooth out the pulsating direct currents.
+    </p>
+    <h2>
+      <a name="chap20" id="chap20">CHAPTER XX</a>
+    </h2>
+    <h3>
+      HOW TO MAKE A RECEIVING SET FOR $5.00 OR LESS
+    </h3>
+    <p>
+      In the chapters on <i>Receptors</i> you have been told how to build up
+      high-grade sets. But there are thousands of boys, and, probably, not a few
+      men, who cannot afford to invest $25.00, more or less, in a receiving set
+      and would like to experiment in a small way.
+    </p>
+    <p>
+      The following set is inexpensive, and with this cheap, little portable
+      receptor you can get the Morse code from stations a hundred miles distant
+      and messages and music from broadcasting stations if you do not live too
+      far away from them. All you need for this set are: (1) a <i>crystal
+      detector</i>, (2) a <i>tuning coil</i> and (3) an <i>earphone</i>. You can
+      make a crystal detector out of a couple of binding posts, a bit of galena
+      and a piece of brass wire, or, better, you can buy one all ready to use
+      for 50 cents.
+    </p>
+    <table cellspacing="20" summary="Illustration">
+      <tr>
+        <td align="center">
+          <i>Photograph unavailable</i>
+        </td>
+      </tr>
+      <tr>
+        <td align="center">
+          Wireless Receptor, the size of a Safety Match Box. A Youthful Genius
+          in the person of Kenneth R. Hinman, Who is only twelve years old, has
+          made a Wireless Receiving Set that fits neatly into a Safety Match
+          Box. With this Instrument and a Pair of Ordinary Receivers, He is able
+          to catch not only Code Messages but the regular Broadcasting Programs
+          from Stations Twenty and Thirty Miles Distant.
+        </td>
+      </tr>
+    </table>
+    <p>
+      <i>The Crystal Detector</i>.--This is known as the <i>Rasco baby</i>
+      detector and it is made and sold by the <i>Radio Specialty Company</i>, 96
+      Park Place, New York City. It is shown in <i>Fig. 96</i>. The base is made
+      of black composition and on it is mounted a standard in which a rod slides
+      and on one end of this there is fixed a hard rubber adjusting knob while
+      the other end carries a thin piece of <i>phosphor-bronze wire</i>, called
+      a <i>cat-whisker</i> To secure the galena crystal in the cup you simply
+      unscrew the knurled cap, place it in the cavity of the post and screw the
+      cap back on again. The free end of the cat-whisker wire is then adjusted
+      so that it will rest lightly on the exposed part of the galena.
+    </p>
+    <p>
+      <a name="fig096" id="fig096"><img width="600" height="347"
+      src="images/fig096.jpg" alt="Fig. 96.--Rasco Baby Crystal Detector." /></a>
+    </p>
+    <p>
+      The <i>Tuning Coil</i>.--You will have to make this tuning coil, which you
+      can do at a cost of less than $1.00, as the cheapest tuning coil you can
+      buy costs at least $3.00, and we need the rest of our $5.00 to invest in
+      the earphone. Get a cardboard tube, such as is used for mailing purposes,
+      2 inches in diameter and 3 inches long, see <i>A</i> in <i>Fig. 97</i>.
+      Now wind on 250 turns of <i>No. 40 Brown and Sharpe gauge plain enameled
+      magnet wire</i>. You can use <i>No. 40 double cotton covered magnet wire</i>,
+      in which case you will have to shellac the tube and the wire after you get
+      it on.
+    </p>
+    <p>
+      <a name="fig097" id="fig097"><img width="600" height="359"
+      src="images/fig097.jpg" alt="Fig. 97.--How the Tuning Coil is Made." /></a>
+    </p>
+    <p>
+      As you wind on the wire take off a tap at every 15th turn, that is, scrape
+      the wire and solder on a piece about 7 inches long, as shown in <i>Fig. 99</i>;
+      and do this until you have 6 taps taken off. Instead of leaving the wires
+      outside of the tube bring them to the inside of it and then out through
+      one of the open ends. Now buy a <i>round wood-base switch</i> with 7
+      contact points on it as shown at <i>B</i> in <i>Fig. 97</i>. This will
+      cost you <i>25</i> or <i>50</i> cents.
+    </p>
+    <p>
+      <i>The Headphone</i>.--An ordinary Bell telephone receiver is of small use
+      for wireless work as it is wound to too low a resistance and the diaphragm
+      is much too thick. If you happen to have a Bell phone you can rewind it
+      with <i>No. 40</i> single covered silk magnet wire, or enameled wire of
+      the same size, when its sensitivity will be very greatly improved. Then
+      you must get a thin diaphragm and this should <i>not</i> be enameled, as
+      this tends to dampen the vibrations of it. You can get a diaphragm of the
+      right kind for 5 cents.
+    </p>
+    <p>
+      The better way, though, is to buy an earphone made especially for wireless
+      work. You can get one wound to 1000 ohms resistance for $1.75 and this
+      price includes a cord. [Footnote: This is Mesco, No. 470 wireless phone.
+      Sold by the Manhattan Electrical Supply Co., Park Place, N.Y.C.] For $1.00
+      extra you can get a head-band for it, and then your phone will look like
+      the one pictured in <i>Fig. 98</i>.
+    </p>
+    <p>
+      <a name="fig098" id="fig098"><img width="345" height="360"
+      src="images/fig098.jpg" alt="Fig. 98.--Mesco 1000 Ohm Head Set." /></a>
+    </p>
+    <p>
+      <i>How to Mount the Parts</i>.--Now mount the coil on a wood base, 1/2 or
+      1 inch thick, 3-1/2 inches wide and 5-1/2 inches long, and then connect
+      one end of the coil to one of the end points on the switch, and connect
+      each succeeding tap to one of the switch points, as shown schematically in
+      <i>Fig. 99</i> and diagrammatically in <i>Fig. 100</i>. This done, screw
+      the switch down to the base. Finally screw the detector to the base and
+      screw two binding posts in front of the coil. These are for the earphone.
+    </p>
+    <p>
+      <a name="fig099" id="fig099"><img width="600" height="554"
+      src="images/fig099.jpg"
+      alt="Fig. 99.--Schematic Layout of $5.00 Receiving Set." /></a> <a
+      name="fig100" id="fig100"><img width="480" height="585"
+      src="images/fig100.jpg"
+      alt="Fig. 100.--Wiring Diagram for $5.00 Receiving Set." /></a>
+    </p>
+    <p>
+      <i>The Condenser</i>.--You do not have to connect a condenser across the
+      earphone but if you do you will improve the receiving qualities of the
+      receptor.
+    </p>
+    <p>
+      <i>How to Connect Up the Receptor</i>.--Now connect up all the parts as
+      shown in <i>Figs. 99</i> and <i>100</i>, then connect the leading-in wire
+      of the aerial with the lever of the switch; and connect the free end of
+      the tuning coil with the <i>ground</i>. If you have no aerial wire try
+      hooking it up to a rain pipe that is <i>not grounded</i> or the steel
+      frame of an umbrella. For a <i>ground</i> you can use a water pipe, an
+      iron pipe driven into the ground, or a hydrant. Put on your headphone,
+      adjust the detector and move the lever over the switch contacts until it
+      is in adjustment and then, if all your connections are properly made, you
+      should be able to pick up messages.
+    </p>
+    <table cellspacing="20" summary="Illustration">
+      <tr>
+        <td align="center">
+          <i>Photograph unavailable</i>
+        </td>
+      </tr>
+      <tr>
+        <td align="center">
+          Wireless Set made into a Ring, designed by Alfred G. Rinehart, of
+          Elizabeth, New Jersey. This little Receptor is a Practical Set; it
+          will receive Messages, Concerts, etc., Measures 1" by 5/8" by 7/8". An
+          ordinary Umbrella is used as an Aerial.
+        </td>
+      </tr>
+    </table>
+    <h2>
+      <a name="appendix" id="appendix">APPENDIX</a>
+    </h2>
+    <h3>
+      USEFUL INFORMATION
+    </h3>
+    <h3>
+      ABBREVIATIONS OF UNITS
+    </h3>
+<pre xml:space="preserve">
+  Unit                   Abbreviation
+
+  ampere                 amp.
+  ampere-hours           amp.-hr.
+  centimeter             cm.
+  centimeter-gram-second c.g.s.
+  cubic centimeters      cm.^3
+  cubic inches           cu. in.
+  cycles per second      ~
+  degrees Centigrade     &deg;C.
+  degrees Fahrenheit     &deg;F.
+  feet                   ft.
+  foot-pounds            ft.-lb.
+  grams                  g.
+  henries                h.
+  inches                 in.
+  kilograms              kg.
+  kilometers             km.
+  kilowatts              kw.
+  kilowatt-hours         kw.-hr.
+  kilovolt-amperes       kv.-a.
+  meters                 m.
+  microfarads            [Greek: mu]f.
+  micromicrofarads       [Greek: mu mu]f.
+  millihenries           mh.
+  millimeters            mm.
+  pounds                 lb.
+  seconds                sec.
+  square centimeters     cm.^2
+  square inches          sq. in.
+  volts                  v.
+  watts                  w.
+</pre>
+    <h3>
+      PREFIXES USED WITH METRIC SYSTEM UNITS
+    </h3>
+<pre xml:space="preserve">
+  Prefix          Abbreviation          Meaning
+
+  micro           [Greek: mu].          1 millionth
+  milli           m.                    1 thousandth
+  centi           c.                    1 hundredth
+  deci            d.                    1 tenth
+  deka            dk.                   10
+  hekto           h.                    1 hundred
+  kilo            k.                    1 thousand
+  mega            m.                    1 million
+</pre>
+    <h3>
+      SYMBOLS USED FOR VARIOUS QUANTITIES
+    </h3>
+    <p>
+      <img width="600" height="530" src="images/symbols-quantities.jpg"
+      alt="Symbols for quantities" />
+    </p>
+<pre xml:space="preserve">
+Quantity                 Symbol
+
+capacitance              <i>C</i>
+
+conductance              <i>g</i>
+
+coupling co-efficient    <i>k</i>
+
+current, instantaneous   <i>i</i>
+
+current, effective value <i>I</i>
+
+decrement                <i>[Greek: delta]</i>
+
+dielectric constant      <i>[Greek: alpha]</i>
+
+electric field intensity <i>[Greek: epsilon]</i>
+
+electromotive force,<br />
+instantaneous value      <i>E</i>
+
+electromotive force,<br />
+effective value          <i>F</i>
+
+energy                   <i>W</i>
+
+force                    <i>F</i>
+
+frequency                <i>f</i>
+
+frequency x 2[Greek: pi] <i>[Greek: omega]</i>
+
+impedance                <i>Z</i>
+
+inductance, self         <i>L</i>
+
+inductance, mutual       <i>M</i>
+
+magnetic field intensity <i>A</i>
+
+magnetic flux            <i>[Greek: Phi]</i>
+
+magnetic induction       <i>B</i>
+
+period of a complete<br />
+oscillation              <i>T</i>
+
+potential difference     <i>V</i>
+
+quantity of electricity  <i>Q</i>
+
+ratio of the<br />
+circumference of a<br />
+circle to its diameter<br />
+=3.1416                  <i>[Greek: pi]</i>
+
+reactance                <i>X</i>
+
+resistance               <i>R</i>
+
+time                     <i>t</i>
+
+velocity                 <i>v</i>
+
+velocity of light        <i>c</i>
+
+wave length              <i>[Greek: lambda]</i>
+
+wave length in meters    <i>[Greek: lambda]m</i>
+
+work                     <i>W</i>
+
+permeability             <i>[Greek: mu]</i>
+
+Square root              <i>[Math: square root]</i>
+</pre>
+    <h3>
+      TABLE OF ENAMELED WIRE
+    </h3>
+<pre xml:space="preserve">
+  No. of   Turns     Turns      Ohms per
+  Wire,     per       per      Cubic Inch
+  B.&amp; S.  Linear    Square        of
+  Gauge    Inch      Inch       Winding
+
+  20        30         885         .748
+  22        37        1400        1.88
+  24        46        2160        4.61
+  26        58        3460       11.80
+  28        73        5400       29.20
+  30        91        8260       70.90
+  32       116      21,000     7547.00
+  34       145      13,430     2968.00
+  36       178      31,820     1098.00
+  38       232      54,080      456.00
+  40       294      86,500      183.00
+</pre>
+    <h3>
+      TABLE OF FREQUENCY AND WAVE LENGTHS
+    </h3>
+<pre xml:space="preserve">
+  W. L.--Wave Lengths in Meters.
+  F.--Number of Oscillations per Second.
+  O. or square root L. C. is called Oscillation Constant.
+  C.--Capacity in Microfarads.
+  L.--Inductance in Centimeters.
+  1000 Centimeters = 1 Microhenry.
+</pre>
+<pre xml:space="preserve">
+    W.L.     F          O       L.C.
+      50  6,000,000     .839       .7039
+     100  3,000,000    1.68       2.82
+     150  2,000,000    2.52       6.35
+     200  1,500,000    3.36      11.29
+     250  1,200,000    4.19      17.55
+     300  1,000,000    5.05      25.30
+     350    857,100    5.87      34.46
+     400    750,000    6.71      45.03
+     450    666,700    7.55      57.00
+     500    600,000    8.39      70.39
+     550    545,400    9.23      85.19
+     600    500,000   10.07     101.41
+     700    428,600   11.74     137.83
+     800    375,000   13.42     180.10
+     900    333,300   15.10     228.01
+   1,000    300,000   16.78     281.57
+   1,100    272,730   18.45     340.40
+   1,200    250,000   20.13     405.20
+   1,300    230,760   21.81     475.70
+   1,400    214,380   23.49     551.80
+   1,500    200,000   25.17     633.50
+   1,600    187,500   26.84     720.40
+   1,700    176,460   28.52     813.40
+   1,800    166,670   30.20     912.00
+   1,900    157,800   31.88   1,016.40
+   2,000    150,000   33.55   1,125.60
+   2,100    142,850   35.23   1,241.20
+   2,200    136,360   36.91   1,362.40
+   2,300    130,430   38.59   1,489.30
+   2,400    125,000   40.27   1,621.80
+   2,500    120,000   41.95   1,759.70
+   2,600    115,380   43.62   1,902.60
+   2,700    111,110   45.30   2,052.00
+   2,800    107,140   46.89   2,207.00
+   2,900    103,450   48.66   2,366.30
+   3,000    100,000   50.33   2,533.20
+   4,000     75,000   67.11   4,504.00
+   5,000     60,000   83.89   7,038.00
+   6,000     50,000  100.7   10,130.00
+   7,000     41,800  117.3   13,630.00
+   8,000     37,500  134.1   18,000.00
+   9,000     33,300  151.0   22,820.00
+  10,000     30,000  167.9   28,150.00
+  11,000     27,300  184.8   34,150.00
+  12,000     25,000  201.5   40,600.00
+  13,000     23,100  218.3   47,600.00
+  14,000     21,400  235.0   55,200.00
+  15,000     20,000  252.0   63,500.00
+  16,000     18,750  269.0   72,300.00
+</pre>
+    <h3>
+      PRONUNCIATION OF GREEK LETTERS
+    </h3>
+    <p>
+      Many of the physical quantities use Greek letters for symbols. The
+      following is the Greek alphabet with the way the letters are pronounced:<br />
+      <img width="600" height="230" src="images/symbols-greek-letters.jpg"
+      alt="Greek symbols" />
+    </p>
+<pre xml:space="preserve">
+  a   alpha
+  b   beta
+  g   gamma
+  d   delta
+  e   epsilon
+  z   zeta
+  ae  eta
+  th  theta
+  i   iota
+  k   kappa
+  l   lambda
+  m   mu
+  n   nu
+  x   Xi(Zi)
+  o   omicron
+  p   pi
+  r   rho
+  s   sigma
+  t   tau
+  u   upsilon
+  ph  phi
+  ch  chi
+  ps  psi
+  o   omega
+</pre>
+    <h3>
+      TABLE OF SPARKING DISTANCES
+    </h3>
+    <p>
+      In Air for Various Voltages between Needle Points
+    </p>
+<pre xml:space="preserve">
+  Volts               Distance
+               Inches         Centimeter
+  5,000         .225            .57
+  10,000        .470           1.19
+  15,000        .725           1.84
+  20,000       1.000           2.54
+  25,000       1.300           3.30
+  30,000       1.625           4.10
+  35,000       2.000           5.10
+  40,000       2.450           6.20
+  45,000       2.95            7.50
+  50,000       3.55            9.90
+  60,000       4.65           11.8
+  70,000       5.85           14.9
+  80,000       7.10           18.0
+  90,000       8.35           21.2
+  100,000      9.60           24.4
+  110,000     10.75           27.3
+  120,000     11.85           30.1
+  130,000     12.95           32.9
+  140,000     13.95           35.4
+  150,000     15.00           38.1
+</pre>
+    <h3>
+      FEET PER POUND OF INSULATED MAGNET WIRE
+    </h3>
+<pre xml:space="preserve">
+  No. of    Single     Double     Single     Double
+  B.&amp; S.    Cotton,    Cotton,    Silk,      Silk,      Enamel
+  Gauge     4-Mils     8-Mils     1-3/4-Mils 4-Mils
+
+  20           311        298       319         312       320
+  21           389        370       408         389       404
+  22           488        461       503         498       509
+  23           612        584       636         631       642
+  24           762        745       800         779       810
+  25           957        903     1,005         966     1,019
+  26         1,192      1,118     1,265       1,202     1,286
+  27         1,488      1,422     1,590       1,543     1,620
+  28         1,852      1,759     1,972       1,917     2,042
+  29         2,375      2,207     2,570       2,435     2,570
+  30         2,860      2,534     3,145       2,900     3,240
+  31         3,800      2,768     3,943       3,683     4,082
+  32         4,375      3,737     4,950       4,654     5,132
+  33         5,590      4,697     6,180       5,689     6,445
+  34         6,500      6,168     7,740       7,111     8,093
+  35         8,050      6,737     9,600       8,584    10,197
+  36         9,820      7,877    12,000      10,039    12,813
+  37        11,860      9,309    15,000      10,666    16,110
+  38        14,300     10,636    18,660      14,222    20,274
+  39        17,130     11,907    23,150      16,516    25,519
+  40        21,590     14,222    28,700      21,333    32,107
+</pre>
+    <h3>
+      INTERNATIONAL MORSE CODE AND CONVENTIONAL SIGNALS
+    </h3>
+    <p>
+      <b>TO BE USED FOR ALL GENERAL PUBLIC SERVICE RADIO COMMUNICATION</b>
+    </p>
+    <ol>
+      <li>
+        A dash is equal to three dots.
+      </li>
+      <li>
+        The space between parts of the same letter is equal to one dot.
+      </li>
+      <li>
+        The space between two letters is equal to three dots.
+      </li>
+      <li>
+        The space between two words is equal to five dots.
+      </li>
+    </ol>
+    <p>
+      [Note: period denotes Morse dot, hyphen denotes Morse dash]
+    </p>
+<pre xml:space="preserve">
+A .-
+
+B -...
+
+C -.-.
+
+D -..
+
+E .
+
+F ..-.
+
+G --.
+
+H ....
+
+I ..
+
+J .---
+
+K -.-
+
+L .-..
+
+M --
+
+N -.
+
+O ---
+
+P .--.
+
+Q --.-
+
+R .-.
+
+S ...
+
+T -
+
+U ..-
+
+V ...-
+
+W .--
+
+X -..-
+
+Y -.--
+
+Z --..
+
+&Auml; (German) .-.-
+
+&Aacute; or &Aring; (Spanish-Scandinavian) .--.-
+
+CH (German-Spanish) ----
+
+&Eacute; (French) ..-..
+
+&Ntilde; (Spanish) --.--
+
+&Ouml; (German) ---.
+
+&Uuml; (German) ..--
+
+1 .----
+
+2 ..---
+
+3 ...--
+
+4 ....-
+
+5 .....
+
+6 -....
+
+7 --...
+
+8 ---..
+
+9 ----.
+
+0 -----
+
+Period .. .. ..
+
+Semicolon -.-.-.
+
+Comma -.-.-.
+
+Colon ---...
+
+Interrogation ..--..
+
+Exclamation point --..--
+
+Apostrophe .----.
+
+Hyphen -....-
+
+Bar indicating fraction -..-.
+
+Parenthesis -.--.-
+
+Inverted commas .-..-.
+
+Underline ..--.-
+
+Double dash -...-
+
+Distress Call ...---...
+
+Attention call to precede every transmission -.-.-
+
+General inquiry call -.-. --.-
+
+From (de) -.. .
+
+Invitation to transmit (go ahead) -.-
+
+Warning--high power --..--
+
+Question (please repeat after ...)--interrupting long messages ..--..
+
+Wait .-...
+
+Break (Bk.) (double dash) -...-
+
+Understand ...-.
+
+Error ........
+
+Received (O.K.) .-.
+
+Position report (to precede all position messages) - .-.
+
+End of each message (cross) .-.-.
+
+Transmission finished (end of work) (conclusion of correspondence) ...-.-
+
+</pre>
+    <h3>
+      INTERNATIONAL RADIOTELEGRAPHIC CONVENTION
+    </h3>
+    <p>
+      <b>LIST OF ABBREVIATIONS TO BE USED IN RADIO COMMUNICATION</b>
+    </p>
+<pre xml:space="preserve">
+ABBREVIATION      QUESTION                ANSWER OR REPLY
+
+PRB   Do you wish to communicate          I wish to communicate by means
+        by means of the International       of the International Signal Code.
+        Signal Code?
+
+QRA   What ship or coast station is       This is....
+      that?
+
+QRB   What is your distance?              My distance is....
+
+QRC   What is your true bearing?          My true bearing is....
+
+QRD   Where are you bound for?            I am bound for....
+
+QRF   Where are you bound from?           I am bound from....
+
+QRG   What line do you belong to?         I belong to the ... Line.
+
+QRH   What is your wave length in         My wave length is ... meters.
+        meters?
+
+QRJ   How many words have you to send?    I have ... words to send.
+
+QRK   How do you receive me?              I am receiving well.
+
+QRL   Are you receiving badly?            I am receiving badly. Please
+        Shall I send 20?                    send 20.
+                   ...-.                               ...-.
+                   for adjustment?                     for adjustment.
+
+QRM   Are you being interfered with?      I am being interfered with.
+
+QRN   Are the atmospherics strong?        Atmospherics are very strong.
+
+QRO   Shall I increase power?             Increase power.
+
+QRP   Shall I decrease power?             Decrease power.
+
+QRQ   Shall I send faster?                Send faster.
+
+QRS   Shall I send slower?                Send slower.
+
+QRT   Shall I stop sending?               Stop sending.
+
+QRU   Have you anything for me?           I have nothing for you.
+
+QRV   Are you ready?                      I am ready. All right now.
+
+QRW   Are you busy?                       I am busy (or: I am busy with...).
+                                            Please do not interfere.
+
+QRX   Shall I stand by?                   Stand by. I will call you when
+                                            required.
+
+QRY   When will be my turn?               Your turn will be No....
+
+QRZ   Are my signals weak?                You signals are weak.
+
+QSA   Are my signals strong?              You signals are strong.
+
+QSB   Is my tone bad?                     The tone is bad.
+      Is my spark bad?                    The spark is bad.
+
+QSC   Is my spacing bad?                  Your spacing is bad.
+
+QSD   What is your time?                  My time is....
+
+QSF   Is transmission to be in            Transmission will be in
+       alternate  order or in series?       alternate order.
+
+QSG                                       Transmission will be in a
+                                            series of 5 messages.
+
+QSH                                       Transmission will be in a
+                                            series of 10  messages.
+
+QSJ   What rate shall I collect for...?   Collect....
+
+QSK   Is the last radiogram canceled?     The last radiogram is canceled.
+
+QSL   Did you get my receipt?             Please acknowledge.
+
+QSM   What is your true course?           My true course is...degrees.
+
+QSN   Are you in communication with land? I am not in communication with land.
+
+QSO   Are you in communication with       I am in communication with...
+        any ship or station                 (through...).
+        (or: with...)?
+
+QSP   Shall I inform...that you are       Inform...that I am calling him.
+        calling him?
+
+QSQ   Is...calling me?                    You are being called by....
+
+QSR   Will you forward the radiogram?     I will forward the radiogram.
+
+QST   Have you received the general       General call to all stations.
+        call?
+
+QSU   Please call me when you have        Will call when I have finished.
+        finished (or: at...o'clock)?
+
+QSV  Is public correspondence being       Public correspondence is being
+       handled?                             handled. Please do not interfere.
+</pre>
+    <p>
+      [Footnote: Public correspondence is any radio work, official or private,
+      handled on commercial wave lengths.]
+    </p>
+<pre xml:space="preserve">
+QSW   Shall I increase my spark           Increase your spark frequency.
+        frequency?
+
+QSX   Shall I decrease my spark           Decrease your spark frequency.
+        frequency?
+
+QSY   Shall I send on a wavelength        Let us change to the wave length
+        of ... meters?                        of ... meters.
+
+QSZ                                       Send each word twice.  I have
+                                            difficulty in receiving you.
+
+QTA                                       Repeat the last radiogram.
+</pre>
+    <p>
+      When an abbreviation is followed by a mark of interrogation, it refers to
+      the question indicated for that abbreviation.
+    </p>
+    <p>
+      <b>Useful Information</b>
+    </p>
+    <h3>
+      Symbols Used For Apparatus
+    </h3>
+    <p>
+      <img width="509" height="800" src="images/symbols-apparatus.jpg"
+      alt="Symbols" />
+    </p>
+    <p>
+      alternator<br /> ammeter<br /> aerial<br /> arc<br /> battery<br /> buzzer<br />
+      condenser<br /> variable condenser<br /> connection of wires<br /> no
+      connection<br /> coupled coils<br /> variable coupling<br /> detector<br />
+      gap, plain<br /> gap, quenched<br /> ground<br /> hot wire ammeter<br />
+      inductor<br /> variable inductor<br /> key<br /> resistor<br /> variable
+      resistor<br /> switch s.p.s.t.<br /> " s.p.d.t.<br /> " d.p.s.t.<br /> "
+      d.p.d.t.<br /> " reversing<br /> phone receiver<br /> " transmitter<br />
+      thermoelement<br /> transformer<br /> vacuum tube<br /> voltmeter<br /> choke
+      coil
+    </p>
+    <h3>
+      DEFINITIONS OF ELECTRIC AND MAGNETIC UNITS
+    </h3>
+    <p>
+      The <i>ohm</i> is the resistance of a thread of mercury at the temperature
+      of melting ice, 14.4521 grams in mass, of uniform cross-section and a
+      length of 106.300 centimeters.
+    </p>
+    <p>
+      The <i>ampere</i> is the current which when passed through a solution of
+      nitrate of silver in water according to certain specifications, deposits
+      silver at the rate of 0.00111800 of a gram per second.
+    </p>
+    <p>
+      The <i>volt</i> is the electromotive force which produces a current of 1
+      ampere when steadily applied to a conductor the resistance of which is 1
+      ohm.
+    </p>
+    <p>
+      The <i>coulomb</i> is the quantity of electricity transferred by a current
+      of 1 ampere in 1 second.
+    </p>
+    <p>
+      The <i>ampere-hour</i> is the quantity of electricity transferred by a
+      current of 1 ampere in 1 hour and is, therefore, equal to 3600 coulombs.
+    </p>
+    <p>
+      The <i>farad</i> is the capacitance of a condenser in which a potential
+      difference of 1 volt causes it to have a charge of 1 coulomb of
+      electricity.
+    </p>
+    <p>
+      The <i>henry</i> is the inductance in a circuit in which the electromotive
+      force induced is 1 volt when the inducing current varies at the rate of 1
+      ampere per second.
+    </p>
+    <p>
+      The <i>watt</i> is the power spent by a current of 1 ampere in a
+      resistance of 1 ohm.
+    </p>
+    <p>
+      The <i>joule</i> is the energy spent in I second by a flow of 1 ampere in
+      1 ohm.
+    </p>
+    <p>
+      The <i>horse-power</i> is used in rating steam machinery. It is equal to
+      746 watts.
+    </p>
+    <p>
+      The <i>kilowatt</i> is 1,000 watts.
+    </p>
+    <p>
+      The units of capacitance actually used in wireless work are the <i>microfarad</i>,
+      which is the millionth part of a farad, because the farad is too large a
+      unit; and the <i>C. G. S. electrostatic unit of capacitance</i>, which is
+      often called the <i>centimeter of capacitance</i>, which is about equal to
+      1.11 microfarads.
+    </p>
+    <p>
+      The units of inductance commonly used in radio work are the <i>millihenry</i>,
+      which is the thousandth part of a henry; and the <i>centimeter of
+      inductance</i>, which is one one-thousandth part of a microhenry.
+    </p>
+    <p>
+      <i>Note</i>.--For further information about electric and magnetic units
+      get the <i>Bureau of Standards Circular No. 60</i>, called <i>Electric
+      Units and Standards</i>, the price of which is 15 cents; also get <i>Scientific
+      Paper No. 292</i>, called <i>International System of Electric and Magnetic
+      Units</i>, price 10 cents. These and other informative papers can be had
+      from the <i>Superintendent of Documents, Government Printing Office</i>,
+      Washington, D. C.
+    </p>
+    <h3>
+      WIRELESS BOOKS
+    </h3>
+    <p>
+      <i>The Admiralty Manual of Wireless Telegraphy</i>. 1920. Published by His
+      Majesty's Stationery Office, London.
+    </p>
+    <p>
+      Ralph E. Batcher.--<i>Prepared Radio Measurements</i>. 1921. Wireless
+      Press, Inc., New York City.
+    </p>
+    <p>
+      Elmer E. Bucher.--<i>Practical Wireless Telegraphy</i>. 1918. Wireless
+      Press, Inc., New York City.
+    </p>
+    <p>
+      Elmer E. Bucher.--<i>Vacuum Tubes in Wireless Communication</i>. 1919.
+      Wireless Press, Inc., New York City.
+    </p>
+    <p>
+      Elmer E. Bucher.--<i>The Wireless Experimenter's Manual</i>. 1920.
+      Wireless Press, Inc., New York City.
+    </p>
+    <ol>
+      <li>
+        Frederick Collins.--<i>Wireless Telegraphy, Its History, Theory, and
+        Practice</i>. 1905. McGraw Pub. Co., New York City.
+      </li>
+      <li>
+        H. Dellinger.--<i>Principles Underlying Radio Communication</i>.
+      </li>
+      <li>
+        Signal Corps, U. S. Army, Washington, D. C.
+      </li>
+      <li>
+        M. Dorsett.--<i>Wireless Telegraphy and Telephony</i>. 1920. Wireless
+        Press, Ltd., London.
+      </li>
+      <li>
+        A. Fleming.--<i>Principles of Electric Wave Telegraphy</i>. 1919.
+        Longmans, Green and Co., London.
+      </li>
+    </ol>
+    <p>
+      Charles B. Hayward.--<i>How to Become a Wireless Operator</i>. 1918.
+      American Technical Society, Chicago, Ill.
+    </p>
+    <p>
+      G. D. Robinson.--<i>Manual of Radio Telegraphy and Telephony</i>. 1920.
+      United States Naval Institute, Annapolis, Md.
+    </p>
+    <p>
+      Rupert Stanley.--<i>Textbook of Wireless Telegraphy</i>. 1919. Longmans,
+      Green and Co., London.
+    </p>
+    <p>
+      E. W. Stone.--<i>Elements of Radio Telegraphy</i>. 1919. D, Van Nostrand
+      Co., New York City.
+    </p>
+    <p>
+      L. B. Turner.--<i>Wireless Telegraphy and Telephony</i>. 1921. Cambridge
+      University Press. Cambridge, England.
+    </p>
+    <p>
+      Send to the <i>Superintendent of Documents, Government Printing Office</i>,
+      Washington, D. C., for a copy of <i>Price List No. 64</i> which lists the
+      Government's books and pamphlets on wireless. It will be sent to you free
+      of charge.
+    </p>
+    <p>
+      The Government publishes; (1) <i>A List of Commercial Government and
+      Special Wireless Stations</i>, every year, price 15 cents; (2) <i>A List
+      of Amateur Wireless Stations</i>, yearly, price 15 cents; (3) <i>A
+      Wireless Service Bulletin</i> is published monthly, price 5 cents a copy,
+      or 25 cents yearly; and (4) <i>Wireless Communication Laws of the United
+      States</i>, the <i>International Wireless Telegraphic Convention and
+      Regulations Governing Wireless Operators and the Use of Wireless on Ships
+      and Land Stations</i>, price 15 cents a copy. Orders for the above
+      publications should be addressed to the <i>Superintendent of Documents,
+      Government Printing Office, Washington, D. C.</i>
+    </p>
+    <h3>
+      Manufacturers and Dealers in Wireless Apparatus and Supplies:
+    </h3>
+    <p>
+      Adams-Morgan Co., Upper Montclair, N. J.
+    </p>
+    <p>
+      American Hard Rubber Co., 11 Mercer Street, New York City.
+    </p>
+    <p>
+      American Radio and Research Corporation, Medford Hillside, Mass.
+    </p>
+    <p>
+      Brach (L. S.) Mfg. Co., 127 Sussex Ave., Newark, N. J.
+    </p>
+    <p>
+      Brandes (C.) Inc., 237 Lafayette St., New York City.
+    </p>
+    <p>
+      Bunnell (J. H.) Company, Park Place, New York City.
+    </p>
+    <p>
+      Burgess Battery Company, Harris Trust Co. Bldg., Chicago, Ill.
+    </p>
+    <p>
+      Clapp-Eastman Co., 120 Main St., Cambridge, Mass.
+    </p>
+    <p>
+      Connecticut Telephone and Telegraph Co., Meriden, Conn.
+    </p>
+    <p>
+      Continental Fiber Co., Newark, Del.
+    </p>
+    <p>
+      Coto-Coil Co., Providence, R. I.
+    </p>
+    <p>
+      Crosley Mfg. Co., Cincinnati, Ohio.
+    </p>
+    <p>
+      Doolittle (F. M.), 817 Chapel St., New Haven, Conn.
+    </p>
+    <p>
+      Edelman (Philip E.), 9 Cortlandt St., New York City.
+    </p>
+    <p>
+      Edison Storage Battery Co., Orange, N. J.
+    </p>
+    <p>
+      Electric Specialty Co., Stamford, Conn.
+    </p>
+    <p>
+      Electrose Mfg. Co., 60 Washington St., Brooklyn, N. Y.
+    </p>
+    <p>
+      General Electric Co., Schenectady, N. Y.
+    </p>
+    <p>
+      Grebe (A. H.) and Co., Inc., Richmond Hill, N. Y. C.
+    </p>
+    <p>
+      International Brass and Electric Co., 176 Beekman St., New York City.
+    </p>
+    <p>
+      International Insulating Co., 25 West 45th St., New York City.
+    </p>
+    <p>
+      King Amplitone Co., 82 Church St., New York City.
+    </p>
+    <p>
+      Kennedy (Colin B.) Co., Rialto Bldg., San Francisco, Cal.
+    </p>
+    <p>
+      Magnavox Co., Oakland, Cal.
+    </p>
+    <p>
+      Manhattan Electrical Supply Co., Park Place, N. Y.
+    </p>
+    <p>
+      Marshall-Gerken Co., Toledo, Ohio.
+    </p>
+    <p>
+      Michigan Paper Tube and Can Co., 2536 Grand River Ave., Detroit, Mich.
+    </p>
+    <p>
+      Murdock (Wm. J.) Co., Chelsea, Mass.
+    </p>
+    <p>
+      National Carbon Co., Inc., Long Island City, N. Y.
+    </p>
+    <p>
+      Pittsburgh Radio and Appliance Co., 112 Diamond St., Pittsburgh, Pa,
+    </p>
+    <p>
+      Radio Corporation of America, 233 Broadway, New York City.
+    </p>
+    <p>
+      Riley-Klotz Mfg. Co., 17-19 Mulberry St., Newark, N. J.
+    </p>
+    <p>
+      Radio Specialty Co., 96 Park Place, New York City.
+    </p>
+    <p>
+      Roller-Smith Co., 15 Barclay St., New York City.
+    </p>
+    <p>
+      Tuska (C. D.) Co., Hartford, Conn.
+    </p>
+    <p>
+      Western Electric Co., Chicago, Ill.
+    </p>
+    <p>
+      Westinghouse Electric Co., Pittsburgh, Pa.
+    </p>
+    <p>
+      Weston Electrical Instrument Co., 173 Weston Ave., Newark, N. J.
+    </p>
+    <p>
+      Westfield Machine Co., Westfield, Mass.
+    </p>
+    <h3>
+      ABBREVIATIONS OF COMMON TERMS
+    </h3>
+<pre xml:space="preserve">
+A. ..............Aerial
+
+A.C. ............Alternating Current
+
+A.F. ............Audio Frequency
+
+B. and S. .......Brown &amp; Sharpe Wire Gauge
+
+C. ..............Capacity or Capacitance
+
+C.G.S. ..........Centimeter-Grain-Second
+
+Cond. ...........Condenser
+
+Coup. ...........Coupler
+
+C.W. ............Continuous Waves
+
+D.C. ............Direct Current
+
+D.P.D.T. ........Double Point Double Throw
+
+D.P.S.T. ........Double Point Single Throw
+
+D.X. ............Distance
+
+E. ..............Short for Electromotive Force (Volt)
+
+E.M.F. ..........Electromotive Force
+
+F. ..............Filament or Frequency
+
+G. ..............Grid
+
+Gnd. ............Ground
+
+I. ..............Current Strength (Ampere)
+
+I.C.W. ..........Interrupted Continuous Waves
+
+KW. .............Kilowatt
+
+L. ..............Inductance
+
+L.C. ............Loose Coupler
+
+Litz. ...........Litzendraht
+
+Mfd. ............Microfarad
+
+Neg. ............Negative
+
+O.T. ............Oscillation Transformer
+
+P. ..............Plate
+
+Prim. ...........Primary
+
+Pos. ............Positive
+
+R. ..............Resistance
+
+R.F. ............Radio Frequency
+
+Sec. ............Secondary
+
+S.P.D.T. ........Single Point Double Throw
+
+S.P.S.T. ........Single Point Single Throw
+
+S.R. ............Self Rectifying
+
+T. ..............Telephone or Period (time) of Complete
+                    Oscillation
+
+Tick. ...........Tickler
+
+V. ..............Potential Difference
+
+Var. ............Variometer
+
+Var. Cond. ......Variable Condenser
+
+V.T. ............Vacuum Tube
+
+W.L. ............Wave Length
+
+X. ..............Reactance
+</pre>
+    <h2>
+      <a name="glossary" id="glossary">GLOSSARY</a>
+    </h2>
+    <p>
+      <i>A</i> BATTERY.--<i>See Battery A</i>.
+    </p>
+    <p>
+      ABBREVIATIONS, CODE.--Abbreviations of questions and answers used in
+      wireless communication. The abbreviation <i>of a question</i> is usually
+      in three letters of which the first is Q. Thus Q R B is the code
+      abbreviation of "<i>what is your distance?</i>" and the answer "<i>My
+      distance is</i>..." See <i>Page 306</i> [Appendix: List of Abbreviations].
+    </p>
+    <p>
+      ABBREVIATIONS, UNITS.--Abbreviations of various units used in wireless
+      electricity. These abbreviations are usually lower case letters of the
+      Roman alphabet, but occasionally Greek letters are used and other signs.
+      Thus <i>amperes</i> is abbreviated <i>amp., micro</i>, which means <i>one
+      millionth</i>, [Greek: mu], etc. See <i>Page 301</i> [Appendix: Useful
+      Abbreviations].
+    </p>
+    <p>
+      ABBREVIATIONS OF WORDS AND TERMS.--Letters used instead of words and terms
+      for shortening them up where there is a constant repetition of them, as <i>A.C.</i>
+      for <i>alternating current; C.W.</i> for <i>continuous waves; V.T.</i> for
+      <i>vacuum tube</i>, etc. See <i>Page 312</i> [Appendix: Abbreviations of
+      Common Terms].
+    </p>
+    <p>
+      AERIAL.--Also called <i>antenna</i>. An aerial wire. One or more wires
+      suspended in the air and insulated from its supports. It is the aerial
+      that sends out the waves and receives them.
+    </p>
+    <p>
+      AERIAL, AMATEUR.--An aerial suitable for sending out 200 meter wave
+      lengths. Such an aerial wire system must not exceed 120 feet in length
+      from the ground up to the aerial switch and from this through the
+      leading-in wire to the end of the aerial.
+    </p>
+    <p>
+      AERIAL AMMETER.--See <i>Ammeter, Hot Wire</i>.
+    </p>
+    <p>
+      AERIAL, BED-SPRINGS.--Where an outdoor aerial is not practicable <i>bed-springs</i>
+      are often made to serve the purpose.
+    </p>
+    <p>
+      AERIAL CAPACITY.--See <i>Capacity, Aerial.</i>
+    </p>
+    <p>
+      AERIAL COUNTERPOISE.--Where it is not possible to get a good ground an <i>aerial
+      counterpoise</i> or <i>earth capacity</i> can be used to advantage. The
+      counterpoise is made like the aerial and is supported directly under it
+      close to the ground but insulated from it.
+    </p>
+    <p>
+      AERIAL, DIRECTIONAL.--A flat-top or other aerial that will transmit and
+      receive over greater distances to and from one direction than to and from
+      another.
+    </p>
+    <p>
+      AERIAL, GROUND.--Signals can be received on a single long wire when it is
+      placed on or buried in the earth or immersed in water. It is also called a
+      <i>ground antenna</i> and an <i>underground aerial.</i>
+    </p>
+    <p>
+      AERIAL, LOOP.--Also called a <i>coil aerial, coil antenna, loop aerial,
+      loop antenna</i> and when used for the purpose a <i>direction finder</i>.
+      A coil of wire wound on a vertical frame.
+    </p>
+    <p>
+      AERIAL RESISTANCE.--See <i>Resistance, Aerial.</i>
+    </p>
+    <p>
+      AERIAL SWITCH.--See <i>Switch Aerial.</i>
+    </p>
+    <p>
+      AERIAL WIRE.--(1) A wire or wires that form the aerial. (2) Wire that is
+      used for aerials; this is usually copper or copper alloy.
+    </p>
+    <p>
+      AERIAL WIRE SYSTEM.--An aerial and ground wire and that part of the
+      inductance coil which connects them. The open oscillation circuit of a
+      sending or a receiving station.
+    </p>
+    <p>
+      AIR CORE TRANSFORMER.--See <i>Transformer, Air Core.</i>
+    </p>
+    <p>
+      AMATEUR AERIAL OR ANTENNA.--See <i>Aerial, Amateur.</i>
+    </p>
+    <p>
+      ALTERNATOR.--An electric machine that generates alternating current.
+    </p>
+    <p>
+      ALPHABET, INTERNATIONAL CODE.--A modified Morse alphabet of dots and
+      dashes originally used in Continental Europe and, hence, called the <i>Continental
+      Code</i>. It is now used for all general public service wireless
+      communication all over the world and, hence, it is called the <i>International
+      Code</i>. See <i>page 305</i> [Appendix: International Morse Code].
+    </p>
+    <p>
+      ALTERNATING CURRENT (<i>A.C.</i>)--See <i>Current.</i>
+    </p>
+    <p>
+      ALTERNATING CURRENT TRANSFORMER.--See <i>Transformer</i>.
+    </p>
+    <p>
+      AMATEUR GROUND.--See <i>Ground, Amateur</i>.
+    </p>
+    <p>
+      AMMETER.--An instrument used for measuring the current strength, in terms
+      of amperes, that flows in a circuit. Ammeters used for measuring direct
+      and alternating currents make use of the <i>magnetic effects</i> of the
+      currents. High frequency currents make use of the <i>heating effects</i>
+      of the currents.
+    </p>
+    <p>
+      AMMETER, HOT-WIRE.--High frequency currents are usually measured by means
+      of an instrument which depends on heating a wire or metal strip by the
+      oscillations. Such an instrument is often called a <i>thermal ammeter</i>,
+      <i>radio ammeter</i> and <i>aerial ammeter</i>.
+    </p>
+    <p>
+      AMMETER, AERIAL.--See <i>Ammeter, Hot Wire</i>.
+    </p>
+    <p>
+      AMMETER, RADIO.--See <i>Ammeter, Hot Wire</i>.
+    </p>
+    <p>
+      AMPERE.--The current which when passed through a solution of nitrate of
+      silver in water according to certain specifications, deposits silver at
+      the rate of 0.00111800 of a gram per second.
+    </p>
+    <p>
+      AMPERE-HOUR.--The quantity of electricity transferred by a current of 1
+      ampere in 1 hour and is, therefore, equal to 3600 coulombs.
+    </p>
+    <p>
+      AMPERE-TURNS.--When a coil is wound up with a number of turns of wire and
+      a current is made to flow through it, it behaves like a magnet. B The
+      strength of the magnetic field inside of the coil depends on (1) the
+      strength of the current and (2) the number of turns of wire on the coil.
+      Thus a feeble current flowing through a large number of turns will produce
+      as strong a magnetic field as a strong current flowing through a few turns
+      of wire. This product of the current in amperes times the number of turns
+      of wire on the coil is called the <i>ampere-turns</i>.
+    </p>
+    <p>
+      AMPLIFICATION, AUDIO FREQUENCY.--A current of audio frequency that is
+      amplified by an amplifier tube or other means.
+    </p>
+    <p>
+      AMPLIFICATION, CASCADE.--See <i>Cascade Amplification</i>.
+    </p>
+    <p>
+      AMPLIFICATION, RADIO FREQUENCY.--A current of radio frequency that is
+      amplified by an amplifier tube or other means before it reaches the
+      detector.
+    </p>
+    <p>
+      AMPLIFICATION, REGENERATIVE.--A scheme that uses a third circuit to feed
+      back part of the oscillations through a vacuum tube and which increases
+      its sensitiveness when used as a detector and multiplies its action as an
+      amplifier and an oscillator.
+    </p>
+    <p>
+      AMPLIFIER, AUDIO FREQUENCY.--A vacuum tube or other device that amplifies
+      the signals after passing through the detector.
+    </p>
+    <p>
+      AMPLIFIER, MAGNETIC.--A device used for controlling radio frequency
+      currents either by means of a telegraph key or a microphone transmitter.
+      The controlling current flows through a separate circuit from that of the
+      radio current and a fraction of an ampere will control several amperes in
+      the aerial wire.
+    </p>
+    <p>
+      AMPLIFIERS, MULTI-STAGE.--A receiving set using two or more amplifiers.
+      Also called <i>cascade amplification</i>.
+    </p>
+    <p>
+      AMPLIFIER, VACUUM TUBE.--A vacuum tube that is used either to amplify the
+      radio frequency currents or the audio frequency currents.
+    </p>
+    <p>
+      AMPLITUDE OF WAVE.--The greatest distance that a point moves from its
+      position of rest.
+    </p>
+    <p>
+      AMPLIFYING TRANSFORMER, AUDIO.--See <i>Transformer, Audio Amplifying</i>.
+    </p>
+    <p>
+      AMPLIFYING MODULATOR VACUUM TUBE.--See <i>Vacuum Tube, Amplifying
+      Modulator</i>.
+    </p>
+    <p>
+      AMPLIFYING TRANSFORMER RADIO.--See <i>Transformer, Radio Amplifying</i>.
+    </p>
+    <p>
+      ANTENNA, AMATEUR.--See <i>Aerial, Amateur</i>.
+    </p>
+    <p>
+      ANTENNA SWITCH.--See <i>Switch, Aerial</i>.
+    </p>
+    <p>
+      APPARATUS SYMBOLS.--See <i>Symbols, Apparatus</i>.
+    </p>
+    <p>
+      ARMSTRONG CIRCUIT.--See <i>Circuit, Armstrong</i>.
+    </p>
+    <p>
+      ATMOSPHERICS.--Same as <i>Static</i>, which see.
+    </p>
+    <p>
+      ATTENUATION.--In Sending wireless telegraph and telephone messages the
+      amplitude of the electric waves is damped out as the distance increases.
+      This is called <i>attenuation</i> and it increases as the frequency is
+      increased. This is the reason why short wave lengths will not carry as far
+      as long wave lengths.
+    </p>
+    <p>
+      AUDIO FREQUENCY AMPLIFIER.--See <i>Amplifier, Audio Frequency</i>.
+    </p>
+    <p>
+      AUDIO FREQUENCY AMPLIFICATION.--See <i>Amplification, Audio Frequency</i>.
+    </p>
+    <p>
+      AUDIBILITY METER.--See <i>Meter, Audibility</i>.
+    </p>
+    <p>
+      AUDIO FREQUENCY.--See <i>Frequency, Audio</i>.
+    </p>
+    <p>
+      AUDIO FREQUENCY CURRENT.--See <i>Current, Audio Frequency</i>.
+    </p>
+    <p>
+      AUDION.--An early trade name given to the vacuum tube detector.
+    </p>
+    <p>
+      AUTODYNE RECEPTOR.--See <i>Receptor, Autodyne</i>.
+    </p>
+    <p>
+      AUTO TRANSFORMER.--See <i>Transformer, Auto</i>.
+    </p>
+    <p>
+      BAKELITE.--A manufactured insulating compound.
+    </p>
+    <p>
+      B BATTERY.--See <i>Battery B</i>.
+    </p>
+    <p>
+      BAND, WAVE LENGTH.--See <i>Wave Length Band</i>.
+    </p>
+    <p>
+      BASKET WOUND COILS.--See <i>Coils, Inductance</i>.
+    </p>
+    <p>
+      BATTERY, A.--The 6-volt storage battery used to heat the filament of a
+      vacuum tube, detector or amplifier.
+    </p>
+    <p>
+      BATTERY, B.--The 22-1/2-volt dry cell battery used to energize the plate
+      of a vacuum tube detector or amplifier.
+    </p>
+    <p>
+      BATTERY, BOOSTER.--This is the battery that is connected in series with
+      the crystal detector.
+    </p>
+    <p>
+      BATTERY, C.--A small dry cell battery sometimes used to give the grid of a
+      vacuum tube detector a bias potential.
+    </p>
+    <p>
+      BATTERY, EDISON STORAGE.--A storage battery in which the elements are made
+      of nickel and iron and immersed in an alkaline <i>electrolyte</i>.
+    </p>
+    <p>
+      BATTERY, LEAD STORAGE.--A storage battery in which the elements are made
+      of lead and immersed in an acid electrolyte.
+    </p>
+    <p>
+      BATTERY POLES.--See <i>Poles, Battery</i>.
+    </p>
+    <p>
+      BATTERY, PRIMARY.--A battery that generates current by chemical action.
+    </p>
+    <p>
+      BATTERY, STORAGE.--A battery that develops a current after it has been
+      charged.
+    </p>
+    <p>
+      BEAT RECEPTION.--See <i>Heterodyne Reception</i>.
+    </p>
+    <p>
+      BED SPRINGS AERIAL.--See <i>Aerial, Bed Springs</i>.
+    </p>
+    <p>
+      BLUB BLUB.--Over modulation in wireless telephony.
+    </p>
+    <p>
+      BROAD WAVE.--See <i>Wave, Broad</i>.
+    </p>
+    <p>
+      BRUSH DISCHARGE.--See <i>Discharge</i>.
+    </p>
+    <p>
+      BUZZER MODULATION.--See <i>Modulation, Buzzer</i>.
+    </p>
+    <p>
+      BLUE GLOW DISCHARGE.--See <i>Discharge</i>.
+    </p>
+    <p>
+      BOOSTER BATTERY.--See <i>Battery, Booster</i>.
+    </p>
+    <p>
+      BROADCASTING.--Sending out intelligence and music from a central station
+      for the benefit of all who live within range of it and who have receiving
+      sets.
+    </p>
+    <p>
+      CAPACITANCE.--Also called by the older name of <i>capacity</i>. The
+      capacity of a condenser, inductance coil or other device capable of
+      retaining a charge of electricity. Capacitance is measured in terms of the
+      <i>microfarad</i>.
+    </p>
+    <p>
+      CAPACITIVE COUPLING.--See <i>Coupling, Capacitive</i>.
+    </p>
+    <p>
+      CAPACITY.--Any object that will retain a charge of electricity; hence an
+      aerial wire, a condenser or a metal plate is sometimes called a <i>capacity</i>.
+    </p>
+    <p>
+      CAPACITY, AERIAL.--The amount to which an aerial wire system can be
+      charged. The <i>capacitance</i> of a small amateur aerial is from 0.0002
+      to 0.0005 microfarad.
+    </p>
+    <p>
+      CAPACITY, DISTRIBUTED.--A coil of wire not only has inductance, but also a
+      certain small capacitance. Coils wound with their turns parallel and
+      having a number of layers have a <i>bunched capacitance</i> which produces
+      untoward effects in oscillation circuits. In honeycomb and other stagger
+      wound coils the capacitance is more evenly distributed.
+    </p>
+    <p>
+      CAPACITY REACTANCE.--See <i>Reactance, Capacity</i>.
+    </p>
+    <p>
+      CAPACITY UNIT.--See <i>Farad</i>.
+    </p>
+    <p>
+      CARBON RHEOSTATS.--See <i>Rheostat, Carbon</i>.
+    </p>
+    <p>
+      CARBORUNDUM DETECTOR.--See <i>Detector</i>.
+    </p>
+    <p>
+      CARRIER CURRENT TELEPHONY.--See <i>Wired-Wireless</i>.
+    </p>
+    <p>
+      CARRIER FREQUENCY.--See <i>Frequency, Carrier</i>.
+    </p>
+    <p>
+      CARRIER FREQUENCY TELEPHONY.--See <i>Wired-Wireless</i>.
+    </p>
+    <p>
+      CASCADE AMPLIFICATION.--Two or more amplifying tubes hooked up in a
+      receiving set.
+    </p>
+    <p>
+      CAT WHISKER CONTACT.--A long, thin wire which makes contact with the
+      crystal of a detector.
+    </p>
+    <p>
+      CENTIMETER OF CAPACITANCE.--Equal to 1.11 <i>microfarads</i>.
+    </p>
+    <p>
+      CENTIMETER OF INDUCTANCE.--Equal to one one-thousandth part of a <i>microhenry</i>.
+    </p>
+    <p>
+      CELLULAR COILS.--See <i>Coils, Inductance</i>.
+    </p>
+    <p>
+      C.G.S. ELECTROSTATIC UNIT OF CAPACITANCE.--See <i>Centimeter of
+      Capacitance</i>.
+    </p>
+    <p>
+      CHARACTERISTICS.--The special behavior of a device, such as an aerial, a
+      detector tube, etc.
+    </p>
+    <p>
+      CHARACTERISTICS, GRID.--See <i>Grid Characteristics</i>.
+    </p>
+    <p>
+      CHOKE COILS.--Coils that prevent the high voltage oscillations from
+      surging back into the transformer and breaking down the insulation.
+    </p>
+    <p>
+      CHOPPER MODULATION.--See <i>Modulation, Chopper</i>.
+    </p>
+    <p>
+      CIRCUIT.--Any electrical conductor through which a current can flow. A low
+      voltage current requires a loop of wire or other conductor both ends of
+      which are connected to the source of current before it can flow. A high
+      frequency current will surge in a wire which is open at both ends like the
+      aerial.
+    </p>
+    <ul>
+      <li>
+        <i>Closed Circuit</i>.--A circuit that is continuous.
+      </li>
+      <li>
+        <i>Open Circuit</i>.--A conductor that is not continuous.
+      </li>
+      <li>
+        <i>Coupled Circuits</i>.--Open and closed circuits connected together by
+        inductance coils, condensers or resistances. See <i>coupling</i>.
+      </li>
+      <li>
+        <i>Close Coupled Circuits</i>.--Open and closed circuits connected
+        directly together with a single inductance coil.
+      </li>
+      <li>
+        <i>Loose Coupled Circuits</i>.--Opened and closed currents connected
+        together inductively by means of a transformer.
+      </li>
+      <li>
+        <i>Stand-by Circuits</i>.--Also called <i>pick-up</i> circuits. When
+        listening-in for possible calls from a number of stations, a receiver is
+        used which will respond to a wide band of wave lengths.
+      </li>
+      <li>
+        <i>Armstrong Circuits</i>.--The regenerative circuit invented by Major
+        E. H. Armstrong.
+      </li>
+    </ul>
+    <p>
+      CLOSE COUPLED CIRCUITS.--See <i>Currents, Close Coupled</i>.
+    </p>
+    <p>
+      CLOSED CIRCUIT.--See <i>Circuit, Closed</i>.
+    </p>
+    <p>
+      CLOSED CORE TRANSFORMER.--See <i>Transformer, Closed Core</i>.
+    </p>
+    <p>
+      CODE.--
+    </p>
+    <ul>
+      <li>
+        <i>Continental</i>.--Same as <i>International</i>.
+      </li>
+      <li>
+        <i>International</i>.--On the continent of Europe land lines use the <i>Continental
+        Morse</i> alphabetic code. This code has come to be used throughout the
+        world for wireless telegraphy and hence it is now called the <i>International
+        code</i>. It is given on Page <i>305</i>. [Appendix: International Morse
+        Code].
+      </li>
+      <li>
+        <i>Morse</i>.--The code devised by Samuel F. B. Morse and which is used
+        on the land lines in the U. S.
+      </li>
+      <li>
+        <i>National Electric</i>.--A set of rules and requirements devised by
+        the <i>National Board of Fire Underwriters</i> for the electrical
+        installations in buildings on which insurance companies carry risks.
+        This code also covers the requirements for wireless installations. A
+        copy may be had from the <i>National Board of Fire Underwriters</i>, New
+        York City, or from your insurance agent.
+      </li>
+      <li>
+        <i>National Electric Safety</i>.--<i>The Bureau of Standards</i>,
+        Washington, D. C., have investigated the precautions which should be
+        taken for the safe operation of all electric equipment. A copy of the <i>Bureau
+        of Standards Handbook No. 3</i> can be had for 40 cents from the <i>Superintendent
+        of Documents</i>.
+      </li>
+    </ul>
+    <p>
+      COEFFICIENT OF COUPLING.--See <i>Coupling, Coefficient of</i>.
+    </p>
+    <p>
+      COIL AERIAL.--See <i>Aerial, Loop</i>.
+    </p>
+    <p>
+      COIL ANTENNA.--See <i>Aerial, Loop</i>.
+    </p>
+    <p>
+      COIL, INDUCTION.--An apparatus for changing low voltage direct currents
+      into high voltage, low frequency alternating currents. When fitted with a
+      spark gap the high voltage, low frequency currents are converted into high
+      voltage, high frequency currents. It is then also called a <i>spark coil</i>
+      and a <i>Ruhmkorff coil</i>.
+    </p>
+    <p>
+      COIL, LOADING.--A coil connected in the aerial or closed oscillation
+      circuit so that longer wave lengths can be received.
+    </p>
+    <p>
+      COIL, REPEATING.--See <i>Repeating Coil</i>.
+    </p>
+    <p>
+      COIL, ROTATING.--One which rotates on a shaft instead of sliding as in a
+      <i>loose coupler</i>. The rotor of a <i>variometer</i> or <i>variocoupler</i>
+      is a <i>rotating coil</i>.
+    </p>
+    <p>
+      COILS, INDUCTANCE.--These are the tuning coils used for sending and
+      receiving sets. For sending sets they are formed of one and two coils, a
+      single sending coil is generally called a <i>tuning inductance coil</i>,
+      while a two-coil tuner is called an <i>oscillation transformer</i>.
+      Receiving tuning coils are made with a single layer, single coil, or a
+      pair of coils, when it is called an oscillation <i>transformer</i>. Some
+      tuning inductance coils have more than one layer, they are then called <i>lattice
+      wound</i>, <i>cellular</i>, <i>basket wound</i>, <i>honeycomb</i>, <i>duo-lateral</i>,
+      <i>stagger wound</i>, <i>spider-web</i> and <i>slab</i> coils.
+    </p>
+    <p>
+      COMMERCIAL FREQUENCY.--See <i>Frequency, Commercial</i>.
+    </p>
+    <p>
+      CONDENSER, AERIAL SERIES.--A condenser placed in the aerial wire system to
+      cut down the wave length.
+    </p>
+    <p>
+      CONDENSER, VERNIER.--A small variable condenser used for receiving
+      continuous waves where very sharp tuning is desired.
+    </p>
+    <p>
+      CONDENSER.--All conducting objects with their insulation form capacities,
+      but a <i>condenser</i> is understood to mean two sheets or plates of metal
+      placed closely together but separated by some insulating material.
+    </p>
+    <ul>
+      <li>
+        <i>Adjustable Condenser</i>.--Where two or more condensers can be
+        coupled together by means of plugs, switches or other devices.
+      </li>
+      <li>
+        <i>Aerial Condenser</i>.--A condenser connected in the aerial.
+      </li>
+      <li>
+        <i>Air Condenser</i>.--Where air only separates the sheets of metal.
+      </li>
+      <li>
+        <i>By-Pass Condenser</i>.--A condenser connected in the transmitting
+        currents so that the high frequency currents cannot flow back through
+        the power circuit.
+      </li>
+      <li>
+        <i>Filter Condenser</i>.--A condenser of large capacitance used in
+        combination with a filter reactor for smoothing out the pulsating direct
+        currents as they come from the rectifier.
+      </li>
+      <li>
+        <i>Fixed Condenser</i>.--Where the plates are fixed relatively to one
+        another.
+      </li>
+      <li>
+        <i>Grid Condenser</i>.--A condenser connected in series with the grid
+        lead.
+      </li>
+      <li>
+        <i>Leyden Jar Condenser</i>.--Where glass jars are used.
+      </li>
+      <li>
+        <i>Mica Condenser</i>.--Where mica is used.
+      </li>
+      <li>
+        <i>Oil Condenser</i>.--Where the plates are immersed in oil.
+      </li>
+      <li>
+        <i>Paper Condenser</i>.--Where paper is used as the insulating material.
+      </li>
+      <li>
+        <i>Protective</i>.--A condenser of large capacity connected across the
+        low voltage supply circuit of a transmitter to form a by-path of
+        kick-back oscillations.
+      </li>
+      <li>
+        <i>Variable Condenser</i>.--Where alternate plates can be moved and so
+        made to interleave more or less with a set of fixed plates.
+      </li>
+      <li>
+        <i>Vernier</i>.--A small condenser with a vernier on it so that it can
+        be very accurately varied. It is connected in parallel with the variable
+        condenser used in the primary circuit and is used for the reception of
+        continuous waves where sharp tuning is essential.
+      </li>
+    </ul>
+    <p>
+      CONDENSITE.--A manufactured insulating compound.
+    </p>
+    <p>
+      CONDUCTIVITY.--The conductance of a given length of wire of uniform cross
+      section. The reciprocal of <i>resistivity</i>.
+    </p>
+    <p>
+      CONTACT DETECTORS.--See <i>Detectors, Contact</i>.
+    </p>
+    <p>
+      CONTINENTAL CODE.--See <i>Code, Continental</i>.
+    </p>
+    <p>
+      COULOMB.--The quantity of electricity transferred by a current of 1 ampere
+      in 1 second.
+    </p>
+    <p>
+      CONVECTIVE DISCHARGE.--See <i>Discharge</i>.
+    </p>
+    <p>
+      CONVENTIONAL SIGNALS.--See <i>Signals, Conventional</i>.
+    </p>
+    <p>
+      COUNTER ELECTROMOTIVE FORCE.--See <i>Electromotive Force, Counter</i>.
+    </p>
+    <p>
+      COUNTERPOISE. A duplicate of the aerial wire that is raised a few feet
+      above the earth and insulated from it. Usually no connection is made with
+      the earth itself.
+    </p>
+    <p>
+      COUPLED CIRCUITS.--See <i>Circuit, Coupled</i>.
+    </p>
+    <p>
+      COUPLING.--When two oscillation circuits are connected together either by
+      the magnetic field of an inductance coil, or by the electrostatic field of
+      a condenser.
+    </p>
+    <p>
+      COUPLING, CAPACITIVE.--Oscillation circuits when connected together by
+      condensers instead of inductance coils.
+    </p>
+    <p>
+      COUPLING, COEFFICIENT OF.--The measure of the closeness of the coupling
+      between two coils.
+    </p>
+    <p>
+      COUPLING, INDUCTIVE.--Oscillation circuits when connected together by
+      inductance coils.
+    </p>
+    <p>
+      COUPLING, RESISTANCE.--Oscillation circuits connected together by a
+      resistance.
+    </p>
+    <p>
+      CRYSTAL RECTIFIER.--A crystal detector.
+    </p>
+    <p>
+      CURRENT, ALTERNATING (<i>A.C.</i>).--A low frequency current that surges
+      to and fro in a circuit.
+    </p>
+    <p>
+      CURRENT, AUDIO FREQUENCY.--A current whose frequency is low enough to be
+      heard in a telephone receiver. Such a current usually has a frequency of
+      between 200 and 2,000 cycles per second.
+    </p>
+    <p>
+      CURRENT, PLATE.--The current which flows between the filament and the
+      plate of a vacuum tube.
+    </p>
+    <p>
+      CURRENT, PULSATING.--A direct current whose voltage varies from moment to
+      moment.
+    </p>
+    <p>
+      CURRENT, RADIO FREQUENCY.--A current whose frequency is so high it cannot
+      be heard in a telephone receiver. Such a current may have a frequency of
+      from 20,000 to 10,000,000 per second.
+    </p>
+    <p>
+      CURRENTS, HIGH FREQUENCY.--(1) Currents that oscillate from 10,000 to
+      300,000,000 times per second. (2) Electric oscillations.
+    </p>
+    <p>
+      CURRENTS, HIGH POTENTIAL.--(1) Currents that have a potential of more than
+      10,000 volts. (2) High voltage currents.
+    </p>
+    <p>
+      CYCLE.--(1) A series of changes which when completed are again at the
+      starting point. (2) A period of time at the end of which an alternating or
+      oscillating current repeats its original direction of flow.
+    </p>
+    <p>
+      DAMPING.--The degree to which the energy of an electric oscillation is
+      reduced. In an open circuit the energy of an oscillation set up by a spark
+      gap is damped out in a few swings, while in a closed circuit it is greatly
+      prolonged, the current oscillating 20 times or more before the energy is
+      dissipated by the sum of the resistances of the circuit.
+    </p>
+    <p>
+      DECREMENT.--The act or process of gradually becoming less.
+    </p>
+    <p>
+      DETECTOR.--Any device that will (1) change the oscillations set up by the
+      incoming waves into direct current, that is which will rectify them, or
+      (2) that will act as a relay.
+    </p>
+    <ul>
+      <li>
+        <i>Carborundum</i>.--One that uses a <i>carborundum</i> crystal for the
+        sensitive element. Carborundum is a crystalline silicon carbide formed
+        in the electric furnace.
+      </li>
+      <li>
+        <i>Cat Whisker Contact</i>.--See <i>Cat Whisker Contact</i>.
+      </li>
+      <li>
+        <i>Chalcopyrite</i>.--Copper pyrites. A brass colored mineral used as a
+        crystal for detectors. See <i>Zincite</i>.
+      </li>
+      <li>
+        <i>Contact</i>.--A crystal detector. Any kind of a detector in which two
+        dissimilar but suitable solids make contact.
+      </li>
+      <li>
+        <i>Ferron</i>.--A detector in which iron pyrites are used as the
+        sensitive element.
+      </li>
+      <li>
+        <i>Galena</i>.--A detector that uses a galena crystal for the rectifying
+        element.
+      </li>
+      <li>
+        <i>Iron Pyrites</i>.--A detector that uses a crystal of iron pyrites for
+        its sensitive element.
+      </li>
+      <li>
+        <i>Molybdenite</i>.--A detector that uses a crystal of <i>sulphide of
+        molybdenum</i> for the sensitive element.
+      </li>
+      <li>
+        <i>Perikon</i>.--A detector in which a <i>bornite</i> crystal makes
+        contact with a <i>zincite</i> crystal.
+      </li>
+      <li>
+        <i>Silicon</i>.--A detector that uses a crystal of silicon for its
+        sensitive element.
+      </li>
+      <li>
+        <i>Vacuum Tube</i>.--A vacuum tube (which see) used as a detector.
+      </li>
+      <li>
+        <i>Zincite</i>.--A detector in which a crystal of <i>zincite</i> is used
+        as the sensitive element.
+      </li>
+    </ul>
+    <p>
+      DE TUNING.--A method of signaling by sustained oscillations in which the
+      key when pressed down cuts out either some of the inductance or some of
+      the capacity and hence greatly changes the wave length.
+    </p>
+    <p>
+      DIELECTRIC.--An insulating material between two electrically charged
+      plates in which there is set up an <i>electric strain</i>, or
+      displacement.
+    </p>
+    <p>
+      DIELECTRIC STRAIN.--The electric displacement in a dielectric.
+    </p>
+    <p>
+      DIRECTIONAL AERIAL.--See <i>Aerial, Directional</i>.
+    </p>
+    <p>
+      DIRECTION FINDER.--See <i>Aerial, Loop</i>.
+    </p>
+    <p>
+      DISCHARGE.--(1) A faintly luminous discharge that takes place from the
+      positive pointed terminal of an induction coil, or other high potential
+      apparatus; is termed a <i>brush discharge</i>. (2) A continuous discharge
+      between the terminals of a high potential apparatus is termed a <i>convective
+      discharge</i>. (3) The sudden breaking-down of the air between the balls
+      forming the spark gap is termed a <i>disruptive discharge</i>; also called
+      an <i>electric spark</i>, or just <i>spark</i> for short. (4) When a tube
+      has a poor vacuum, or too large a battery voltage, it glows with a blue
+      light and this is called a <i>blue glow discharge</i>.
+    </p>
+    <p>
+      DISRUPTIVE DISCHARGE.--See <i>Discharge</i>.
+    </p>
+    <p>
+      DISTRESS CALL. [Morse code:] ...---... (SOS).
+    </p>
+    <p>
+      DISTRIBUTED CAPACITY.--See <i>Capacity, Distributed</i>.
+    </p>
+    <p>
+      DOUBLE HUMP RESONANCE CURVE.--A resonance curve that has two peaks or
+      humps which show that the oscillating currents which are set up when the
+      primary and secondary of a tuning coil are closely coupled have two
+      frequencies.
+    </p>
+    <p>
+      DUO-LATERAL COILS.--See <i>Coils, Inductance</i>.
+    </p>
+    <p>
+      DUPLEX COMMUNICATION.--A wireless telephone system with which it is
+      possible to talk between both stations in either direction without the use
+      of switches. This is known as the <i>duplex system</i>.
+    </p>
+    <p>
+      EARTH CAPACITY.--An aerial counterpoise.
+    </p>
+    <p>
+      EARTH CONNECTION.--Metal plates or wires buried in the ground or immersed
+      in water. Any kind of means by which the sending and receiving apparatus
+      can be connected with the earth.
+    </p>
+    <p>
+      EDISON STORAGE BATTERY.--See <i>Storage Battery, Edison</i>.
+    </p>
+    <p>
+      ELECTRIC ENERGY.--The power of an electric current.
+    </p>
+    <p>
+      ELECTRIC OSCILLATIONS.--See <i>Oscillations, Electric</i>.
+    </p>
+    <p>
+      ELECTRIC SPARK.--See <i>Discharge, Spark</i>.
+    </p>
+    <p>
+      ELECTRICITY, NEGATIVE.--The opposite of <i>positive electricity</i>.
+      Negative electricity is formed of negative electrons which make up the
+      outside particles of an atom.
+    </p>
+    <p>
+      ELECTRICITY, POSITIVE.--The opposite of <i>negative electricity</i>.
+      Positive electricity is formed of positive electrons which make up the
+      inside particles of an atom.
+    </p>
+    <p>
+      ELECTRODES.--Usually the parts of an apparatus which dip into a liquid and
+      carry a current. The electrodes of a dry battery are the zinc and carbon
+      elements. The electrodes of an Edison storage battery are the iron and
+      nickel elements, and the electrodes of a lead storage battery are the lead
+      elements.
+    </p>
+    <p>
+      ELECTROLYTES.--The acid or alkaline solutions used in batteries.
+    </p>
+    <p>
+      ELECTROMAGNETIC WAVES.--See <i>Waves, Electric</i>.
+    </p>
+    <p>
+      ELECTROMOTIVE FORCE.--Abbreviated <i>emf</i>. The force that drives an
+      electric current along a conductor. Also loosely called <i>voltage</i>.
+    </p>
+    <p>
+      ELECTROMOTIVE FORCE, COUNTER.--The emf. that is set up in a direction
+      opposite to that in which the current is flowing in a conductor.
+    </p>
+    <p>
+      ELECTRON.--(1) A negative particle of electricity that is detached from an
+      atom. (2) A negative particle of electricity thrown off from the
+      incandescent filament of a vacuum tube.
+    </p>
+    <p>
+      ELECTRON FLOW.--The passage of electrons between the incandescent filament
+      and the cold positively charged plate of a vacuum tube.
+    </p>
+    <p>
+      ELECTRON RELAY.--See <i>Relay, Electron</i>.
+    </p>
+    <p>
+      ELECTRON TUBE.--A vacuum tube or a gas-content tube used for any purpose
+      in wireless work. See <i>Vacuum Tube</i>.
+    </p>
+    <p>
+      ELECTROSE INSULATORS.--Insulators made of a composition material the trade
+      name of which is <i>Electrose</i>.
+    </p>
+    <p>
+      ENERGY, ELECTRIC.--See <i>Electric Energy</i>.
+    </p>
+    <p>
+      ENERGY UNIT.--The <i>joule</i>, which see, <i>Page 308</i> [Appendix:
+      Definitions of Electric and Magnetic Units].
+    </p>
+    <p>
+      FADING.--The sudden variation in strength of signals received from a
+      transmitting station when all the adjustments of both sending and
+      receiving apparatus remain the same. Also called <i>swinging</i>.
+    </p>
+    <p>
+      FARAD.--The capacitance of a condenser in which a potential difference of
+      1 volt causes it to have a charge of 1 coulomb of electricity.
+    </p>
+    <p>
+      FEED-BACK ACTION.--Feeding back the oscillating currents in a vacuum tube
+      to amplify its power. Also called <i>regenerative action</i>.
+    </p>
+    <p>
+      FERROMAGNETIC CONTROL.--See <i>Magnetic Amplifier</i>.
+    </p>
+    <p>
+      FILAMENT.--The wire in a vacuum tube that is heated to incandescence and
+      which throws off electrons.
+    </p>
+    <p>
+      FILAMENT RHEOSTAT.--See <i>Rheostat, Filament</i>.
+    </p>
+    <p>
+      FILTER.--Inductance coils or condensers or both which (1) prevent
+      troublesome voltages from acting on the different circuits, and (2) smooth
+      out alternating currents after they have been rectified.
+    </p>
+    <p>
+      FILTER REACTOR.--See <i>Reactor, Filter</i>.
+    </p>
+    <p>
+      FIRE UNDERWRITERS.--See <i>Code, National Electric</i>.
+    </p>
+    <p>
+      FIXED GAP.--See <i>Gap</i>.
+    </p>
+    <p>
+      FLEMING VALVE.--A two-electrode vacuum tube.
+    </p>
+    <p>
+      FORCED OSCILLATIONS.--See <i>Oscillations, Forced</i>.
+    </p>
+    <p>
+      FREE OSCILLATIONS.--See <i>Oscillations, Free</i>.
+    </p>
+    <p>
+      FREQUENCY, AUDIO.--(1) An alternating current whose frequency is low
+      enough to operate a telephone receiver and, hence, which can be heard by
+      the ear. (2) Audio frequencies are usually around 500 or 1,000 cycles per
+      second, but may be as low as 200 and as high as 10,000 cycles per second.
+    </p>
+    <ul>
+      <li>
+        <i>Carrier</i>.--A radio frequency wave modulated by an audio frequency
+        wave which results in setting of <i>three</i> radio frequency waves. The
+        principal radio frequency is called the carrier frequency, since it
+        carries or transmits the audio frequency wave.
+      </li>
+      <li>
+        <i>Commercial</i>.--(1) Alternating current that is used for commercial
+        purposes, namely, light, heat and power. (2) Commercial frequencies now
+        in general use are from 25 to 50 cycles per second.
+      </li>
+      <li>
+        <i>Natural</i>.--The pendulum and vibrating spring have a <i>natural
+        frequency</i> which depends on the size, material of which it is made,
+        and the friction which it has to overcome. Likewise an oscillation
+        circuit has a natural frequency which depends upon its <i>inductance</i>,
+        <i>capacitance</i> and <i>resistance</i>.
+      </li>
+      <li>
+        <i>Radio</i>.--(1) An oscillating current whose frequency is too high to
+        affect a telephone receiver and, hence, cannot be heard by the ear. (2)
+        Radio frequencies are usually between 20,000 and 2,000,000 cycles per
+        second but may be as low as 10,000 and as high as 300,000,000 cycles per
+        second.
+      </li>
+      <li>
+        <i>Spark.--</i>The number of sparks per second produced by the discharge
+        of a condenser.
+      </li>
+    </ul>
+    <p>
+      GAP, FIXED.--One with fixed electrodes.
+    </p>
+    <p>
+      GAP, NON-SYNCHRONOUS.--A rotary spark gap run by a separate motor which
+      may be widely different from that of the speed of the alternator.
+    </p>
+    <p>
+      GAP, QUENCHED.--(1) A spark gap for the impulse production of oscillating
+      currents. (2) This method can be likened to one where a spring is struck a
+      single sharp blow and then continues to set up vibrations.
+    </p>
+    <p>
+      GAP, ROTARY.--One having fixed and rotating electrodes.
+    </p>
+    <p>
+      GAP, SYNCHRONOUS.--A rotary spark gap run at the same speed as the
+      alternator which supplies the power transformer. Such a gap usually has as
+      many teeth as there are poles on the generator. Hence one spark occurs per
+      half cycle.
+    </p>
+    <p>
+      GAS-CONTENT TUBE.--See <i>Vacuum Tube.</i>
+    </p>
+    <p>
+      GENERATOR TUBE.--A vacuum tube used to set up oscillations. As a matter of
+      fact it does not <i>generate</i> oscillations, but changes the initial low
+      voltage current that flows through it into oscillations. Also called an <i>oscillator
+      tube</i> and a <i>power tube.</i>
+    </p>
+    <p>
+      GRID BATTERY.--See <i>Battery C.</i>
+    </p>
+    <p>
+      GRID CHARACTERISTICS.--The various relations that could exist between the
+      voltages and currents of the grid of a vacuum tube, and the values which
+      do exist between them when the tube is in operation. These characteristics
+      are generally shown by curves.
+    </p>
+    <p>
+      GRID CONDENSER.--See <i>Condenser, Grid.</i>
+    </p>
+    <p>
+      GRID LEAK.--A high resistance unit connected in the grid lead of both
+      sending and receiving sets. In a sending set it keeps the voltage of the
+      grid at a constant value and so controls the output of the aerial. In a
+      receiving set it controls the current flowing between the plate and
+      filament.
+    </p>
+    <p>
+      GRID MODULATION.--See <i>Modulation, Grid.</i>
+    </p>
+    <p>
+      GRID POTENTIAL.--The negative or positive voltage of the grid of a vacuum
+      tube.
+    </p>
+    <p>
+      GRID VOLTAGE.--See <i>Grid Potential.</i>
+    </p>
+    <p>
+      GRINDERS.--The most common form of <i>Static,</i> which see. They make a
+      grinding noise in the headphones.
+    </p>
+    <p>
+      GROUND.--See <i>Earth Connection.</i>
+    </p>
+    <p>
+      GROUND, AMATEUR.--A water-pipe ground.
+    </p>
+    <p>
+      GROUND, WATERPIPE.--A common method of grounding by amateurs is to use the
+      waterpipe, gaspipe or radiator.
+    </p>
+    <p>
+      GUIDED WAVE TELEPHONY.--See <i>Wired Wireless.</i>
+    </p>
+    <p>
+      HARD TUBE.--A vacuum tube in which the vacuum is <i>high,</i> that is,
+      exhausted to a high degree.
+    </p>
+    <p>
+      HELIX.--(1) Any coil of wire. (2) Specifically a transmitter tuning
+      inductance coil.
+    </p>
+    <p>
+      HENRY.--The inductance in a circuit in which the electromotive force
+      induced is 1 volt when the inducing current varies at the rate of 1 ampere
+      per second.
+    </p>
+    <p>
+      HETERODYNE RECEPTION.--(1) Receiving by the <i>beat</i> method. (2)
+      Receiving by means of superposing oscillations generated at the receiving
+      station on the oscillations set up in the aerial by the incoming waves.
+    </p>
+    <p>
+      HETERODYNE RECEPTOR.--See <i>Receptor, Heterodyne.</i>
+    </p>
+    <p>
+      HIGH FREQUENCY CURRENTS.--See <i>Currents, High Frequency.</i>
+    </p>
+    <p>
+      HIGH FREQUENCY RESISTANCE.--See <i>Resistance, High Frequency.</i>
+    </p>
+    <p>
+      HIGH POTENTIAL CURRENTS.--See <i>Currents, High Potential.</i>
+    </p>
+    <p>
+      HIGH VOLTAGE CURRENTS.--See <i>Currents, High Potential.</i>
+    </p>
+    <p>
+      HONEYCOMB COILS.--See <i>Coils, Inductance.</i>
+    </p>
+    <p>
+      HORSE-POWER.--Used in rating steam machinery. It is equal to 746 watts.
+    </p>
+    <p>
+      HOT WIRE AMMETER.--See <i>Ammeter, Hot Wire.</i>
+    </p>
+    <p>
+      HOWLING.--Where more than three stages of radio amplification, or more
+      than two stages of audio amplification, are used howling noises are apt to
+      occur in the telephone receivers.
+    </p>
+    <p>
+      IMPEDANCE.--An oscillation circuit has <i>reactance</i> and also <i>resistance,</i>
+      and when these are combined the total opposition to the current is called
+      <i>impedance.</i>
+    </p>
+    <p>
+      INDUCTANCE COILS.--See <i>Coils, Inductance.</i>
+    </p>
+    <p>
+      INDUCTANCE COIL, LOADING.--See <i>Coil, Loading Inductance.</i>
+    </p>
+    <p>
+      INDUCTIVE COUPLING.--See <i>Coupling, Inductive.</i>
+    </p>
+    <p>
+      INDUCTIVE REACTANCE.--See <i>Reactance, Inductive.</i>
+    </p>
+    <p>
+      INDUCTION COIL.--See <i>Coil, Induction.</i>
+    </p>
+    <p>
+      INDUCTION, MUTUAL.--Induction produced between two circuits or coils close
+      to each other by the mutual interaction of their magnetic fields.
+    </p>
+    <p>
+      INSULATION.--Materials used on and around wires and other conductors to
+      keep the current from leaking away.
+    </p>
+    <p>
+      INSPECTOR, RADIO.--A U. S. inspector whose business it is to issue both
+      station and operators' licenses in the district of which he is in charge.
+    </p>
+    <p>
+      INTERFERENCE.--The crossing or superposing of two sets of electric waves
+      of the same or slightly different lengths which tend to oppose each other.
+      It is the untoward interference between electric waves from different
+      stations that makes selective signaling so difficult a problem.
+    </p>
+    <p>
+      INTERMEDIATE WAVES.--See <i>Waves.</i>
+    </p>
+    <p>
+      IONIC TUBES.--See <i>Vacuum Tubes.</i>
+    </p>
+    <p>
+      INTERNATIONAL CODE.--See Code, International.
+    </p>
+    <p>
+      JAMMING.--Waves that are of such length and strength that when they
+      interfere with incoming waves they drown them out.
+    </p>
+    <p>
+      JOULE.--The energy spent in 1 second by a flow of 1 ampere in 1 ohm.
+    </p>
+    <p>
+      JOULE'S LAW.--The relation between the heat produced in seconds to the
+      resistance of the circuit, to the current flowing in it.
+    </p>
+    <p>
+      KENOTRON.--The trade name of a vacuum tube rectifier made by the <i>Radio
+      Corporation of America.</i>
+    </p>
+    <p>
+      KICK-BACK.--Oscillating currents that rise in voltage and tend to flow
+      back through the circuit that is supplying the transmitter with low
+      voltage current.
+    </p>
+    <p>
+      KICK-BACK PREVENTION.--See <i>Prevention, Kick-Back.</i>
+    </p>
+    <p>
+      KILOWATT.--1,000 watts.
+    </p>
+    <p>
+      LAMBDA.--See <i>Pages 301, 302.</i> [Appendix: Useful Abbreviations].
+    </p>
+    <p>
+      LATTICE WOUND COILS.--See <i>Coils, Inductance.</i>
+    </p>
+    <p>
+      LIGHTNING SWITCH.--See <i>Switch, Lightning.</i>
+    </p>
+    <p>
+      LINE RADIO COMMUNICATION.--See <i>Wired Wireless.</i>
+    </p>
+    <p>
+      LINE RADIO TELEPHONY.--See <i>Telephony, Line Radio.</i>
+    </p>
+    <p>
+      LITZENDRAHT.--A conductor formed of a number of fine copper wires either
+      twisted or braided together. It is used to reduce the <i>skin effect.</i>
+      See <i>Resistance, High Frequency.</i>
+    </p>
+    <p>
+      LOAD FLICKER.--The flickering of electric lights on lines that supply
+      wireless transmitting sets due to variations of the voltage on opening and
+      closing the key.
+    </p>
+    <p>
+      LOADING COIL.--See <i>Coil, Loading.</i>
+    </p>
+    <p>
+      LONG WAVES.--See <i>Waves.</i>
+    </p>
+    <p>
+      LOOP AERIAL.--See <i>Aerial, Loop.</i>
+    </p>
+    <p>
+      LOOSE COUPLED CIRCUITS.--See <i>Circuits, Loose Coupled.</i>
+    </p>
+    <p>
+      LOUD SPEAKER.--A telephone receiver connected to a horn, or a specially
+      made one, that reproduces the incoming signals, words or music loud enough
+      to be heard by a room or an auditorium full of people, or by large crowds
+      out-doors.
+    </p>
+    <p>
+      MAGNETIC POLES.--See <i>Poles, Magnetic.</i>
+    </p>
+    <p>
+      MEGOHM.--One million ohms.
+    </p>
+    <p>
+      METER, AUDIBILITY.--An instrument for measuring the loudness of a signal
+      by comparison with another signal. It consists of a pair of headphones and
+      a variable resistance which have been calibrated.
+    </p>
+    <p>
+      MHO.--The unit of conductance. As conductance is the reciprocal of
+      resistance it is measured by the <i>reciprocal ohm</i> or <i>mho.</i>
+    </p>
+    <p>
+      MICA.--A transparent mineral having a high insulating value and which can
+      be split into very thin sheets. It is largely used in making condensers
+      both for transmitting and receiving sets.
+    </p>
+    <p>
+      MICROFARAD.--The millionth part of a <i>farad.</i>
+    </p>
+    <p>
+      MICROHENRY.--The millionth part of a <i>farad.</i>
+    </p>
+    <p>
+      MICROMICROFARAD.--The millionth part of a <i>microfarad.</i>
+    </p>
+    <p>
+      MICROHM.--The millionth part of an <i>ohm.</i>
+    </p>
+    <p>
+      MICROPHONE TRANSFORMER.--See <i>Transformer, Microphone.</i>
+    </p>
+    <p>
+      MICROPHONE TRANSMITTER.--See <i>Transmitter, Microphone.</i>
+    </p>
+    <p>
+      MILLI-AMMETER.--An ammeter that measures a current by the one-thousandth
+      of an ampere.
+    </p>
+    <p>
+      MODULATION.--(1) Inflection or varying the voice. (2) Varying the
+      amplitude of oscillations by means of the voice.
+    </p>
+    <p>
+      MODULATION, BUZZER.--The modulation of radio frequency oscillations by a
+      buzzer which breaks up the sustained oscillations of a transmitter into
+      audio frequency impulses.
+    </p>
+    <p>
+      MILLIHENRY.--The thousandth part of a <i>henry.</i>
+    </p>
+    <p>
+      MODULATION, CHOPPER.--The modulation of radio frequency oscillations by a
+      chopper which breaks up the sustained oscillations of a transmitter into
+      audio frequency impulses.
+    </p>
+    <p>
+      MODULATION, GRID.--The scheme of modulating an oscillator tube by
+      connecting the secondary of a transformer, the primary of which is
+      connected with a battery and a microphone transmitter, in the grid lead.
+    </p>
+    <p>
+      MODULATION, OVER.--See <i>Blub Blub.</i>
+    </p>
+    <p>
+      MODULATION, PLATE.--Modulating the oscillations set up by a vacuum tube by
+      varying the current impressed on the plate.
+    </p>
+    <p>
+      MODULATOR TUBE.--A vacuum tube used as a modulator.
+    </p>
+    <p>
+      MOTION, WAVE.--(1) The to and fro motion of water at sea. (2) Waves
+      transmitted by, in and through the air, or sound waves. (3) Waves
+      transmitted by, in and through the <i>ether,</i> or <i>electromagnetic
+      waves,</i> or <i>electric waves</i> for short.
+    </p>
+    <p>
+      MOTOR-GENERATOR.--A motor and a dynamo built to run at the same speed and
+      mounted on a common base, the shafts being coupled together. In wireless
+      it is used for changing commercial direct current into direct current of
+      higher voltages for energizing the plate of a vacuum tube oscillator.
+    </p>
+    <p>
+      MULTI-STAGE AMPLIFIERS.--See <i>Amplifiers, Multi-Stage.</i>
+    </p>
+    <p>
+      MUTUAL INDUCTION.--See <i>Induction, Mutual.</i>
+    </p>
+    <p>
+      MUSH.--Irregular intermediate frequencies set up by arc transmitters which
+      interfere with the fundamental wave lengths.
+    </p>
+    <p>
+      MUSHY NOTE.--A note that is not clear cut, and hence hard to read, which
+      is received by the <i>heterodyne method</i> when damped waves or modulated
+      continuous waves are being received.
+    </p>
+    <p>
+      NATIONAL ELECTRIC CODE.--See <i>Code, National Electric.</i>
+    </p>
+    <p>
+      NATIONAL ELECTRIC SAFETY CODE.--See <i>Code, National Electric Safety.</i>
+    </p>
+    <p>
+      NEGATIVE ELECTRICITY.--See <i>Electricity, Negative.</i>
+    </p>
+    <p>
+      NON-SYNCHRONOUS GAP.--See <i>Gap, Non-Synchronous.</i>
+    </p>
+    <p>
+      OHM.--The resistance of a thread of mercury at the temperature of melting
+      ice, 14.4521 grams in mass, of uniform cross-section and a length of
+      106.300 centimeters.
+    </p>
+    <p>
+      OHM'S LAW.--The important fixed relation between the electric current, its
+      electromotive force and the resistance of the conductor in which it flows.
+    </p>
+    <p>
+      OPEN CIRCUIT.--See <i>Circuit, Open.</i>
+    </p>
+    <p>
+      OPEN CORE TRANSFORMER.--See <i>Transformer, Open Core.</i>
+    </p>
+    <p>
+      OSCILLATION TRANSFORMER.--See <i>Transformer, Oscillation.</i>
+    </p>
+    <p>
+      OSCILLATIONS, ELECTRIC.--A current of high frequency that surges through
+      an open or a closed circuit. (1) Electric oscillations may be set up by a
+      spark gap, electric arc or a vacuum tube, when they have not only a high
+      frequency but a high potential, or voltage. (2) When electric waves
+      impinge on an aerial wire they are transformed into electric oscillations
+      of a frequency equal to those which emitted the waves, but since a very
+      small amount of energy is received their potential or voltage is likewise
+      very small.
+    </p>
+    <ul>
+      <li>
+        <i>Sustained.--</i>Oscillations in which the damping factor is small.
+      </li>
+      <li>
+        <i>Damped.--</i>Oscillations in which the damping factor is large.
+      </li>
+      <li>
+        <i>Free.--</i>When a condenser discharges through an oscillation
+        circuit, where there is no outside electromotive force acting on it, the
+        oscillations are said to be <i>free.</i>
+      </li>
+      <li>
+        <i>Forced.--</i>Oscillations that are made to surge in a circuit whose
+        natural period is different from that of the oscillations set up in it.
+      </li>
+    </ul>
+    <p>
+      OSCILLATION TRANSFORMER.--See <i>Transformer.</i>
+    </p>
+    <p>
+      OSCILLATION VALVE.--See <i>Vacuum Tube.</i>
+    </p>
+    <p>
+      OSCILLATOR TUBE.--A vacuum tube which is used to produce electric
+      oscillations.
+    </p>
+    <p>
+      OVER MODULATION.--See <i>Blub Blub.</i>
+    </p>
+    <p>
+      PANCAKE OSCILLATION TRANSFORMER.--Disk-shaped coils that are used for
+      receiving tuning inductances.
+    </p>
+    <p>
+      PERMEABILITY, MAGNETIC.--The degree to which a substance can be
+      magnetized. Iron has a greater magnetic permeability than air.
+    </p>
+    <p>
+      PHASE.--A characteristic aspect or appearance that takes place at the same
+      point or part of a cycle.
+    </p>
+    <p>
+      PICK-UP CIRCUITS.--See <i>Circuits, Stand-by.</i>
+    </p>
+    <p>
+      PLATE CIRCUIT REACTOR.--See <i>Reactor, Plate Circuit.</i>
+    </p>
+    <p>
+      PLATE CURRENT.--See <i>Current, Plate.</i>
+    </p>
+    <p>
+      PLATE MODULATION.--See <i>Modulation, Plate.</i>
+    </p>
+    <p>
+      PLATE VOLTAGE.--See <i>Foliage, Plate.</i>
+    </p>
+    <p>
+      POLES, BATTERY.--The positive and negative terminals of the elements of a
+      battery. On a storage battery these poles are marked + and - respectively.
+    </p>
+    <p>
+      POLES, MAGNETIC.--The ends of a magnet.
+    </p>
+    <p>
+      POSITIVE ELECTRICITY.--See <i>Electricity, Positive.</i>
+    </p>
+    <p>
+      POTENTIAL DIFFERENCE.--The electric pressure between two charged
+      conductors or surfaces.
+    </p>
+    <p>
+      POTENTIOMETER.--A variable resistance used for subdividing the voltage of
+      a current. A <i>voltage divider.</i>
+    </p>
+    <p>
+      POWER TRANSFORMER.--See <i>Transformer, Power.</i>
+    </p>
+    <p>
+      POWER TUBE.--See <i>Generator Tube.</i>
+    </p>
+    <p>
+      PRIMARY BATTERY.--See <i>Battery, Primary.</i>
+    </p>
+    <p>
+      PREVENTION, KICK-BACK.--A choke coil placed in the power circuit to
+      prevent the high frequency currents from getting into the transformer and
+      breaking down the insulation.
+    </p>
+    <p>
+      Q S T.--An abbreviation used in wireless communication for (1) the
+      question "Have you received the general call?" and (2) the notice,
+      "General call to all stations."
+    </p>
+    <p>
+      QUENCHED GAP.--See <i>Gap, Quenched.</i>
+    </p>
+    <p>
+      RADIATION.--The emission, or throwing off, of electric waves by an aerial
+      wire system.
+    </p>
+    <p>
+      RADIO AMMETER.--See <i>Ammeter, Hot Wire.</i>
+    </p>
+    <p>
+      RADIO FREQUENCY.--See <i>Frequency, Radio.</i>
+    </p>
+    <p>
+      RADIO FREQUENCY AMPLIFICATION.--See <i>Amplification, Radio Frequency.</i>
+    </p>
+    <p>
+      RADIO FREQUENCY CURRENT.--See <i>Current, Radio Frequency.</i>
+    </p>
+    <p>
+      RADIO INSPECTOR.--See <i>Inspector, Radio</i>.
+    </p>
+    <p>
+      RADIOTRON.--The trade name of vacuum tube detectors, amplifiers,
+      oscillators and modulators made by the <i>Radio Corporation of America</i>.
+    </p>
+    <p>
+      RADIO WAVES.--See <i>Waves, Radio</i>.
+    </p>
+    <p>
+      REACTANCE.--When a circuit has inductance and the current changes in
+      value, it is opposed by the voltage induced by the variation of the
+      current.
+    </p>
+    <p>
+      REACTANCE, CAPACITY.--The capacity reactance is the opposition offered to
+      a current by a capacity. It is measured as a resistance, that is, in <i>ohms</i>.
+    </p>
+    <p>
+      RECEIVING TUNING COILS.--See <i>Coils, Inductance</i>.
+    </p>
+    <p>
+      RECEIVER, LOUD SPEAKING.--See <i>Loud Speakers</i>.
+    </p>
+    <p>
+      RECEIVER, WATCH CASE.--A compact telephone receiver used for wireless
+      reception.
+    </p>
+    <p>
+      REACTANCE, INDUCTIVE.--The inductive reactance is the opposition offered
+      to the current by an inductance coil. It is measured as a resistance, that
+      is, in <i>ohms</i>.
+    </p>
+    <p>
+      REACTOR, FILTER.--A reactance coil for smoothing out the pulsating direct
+      currents as they come from the rectifier.
+    </p>
+    <p>
+      REACTOR, PLATE CIRCUIT.--A reactance coil used in the plate circuit of a
+      wireless telephone to keep the direct current supply at a constant
+      voltage.
+    </p>
+    <p>
+      RECEIVER.--(1) A telephone receiver. (2) An apparatus for receiving
+      signals, speech or music. (3) Better called a <i>receptor</i> to
+      distinguish it from a telephone receiver.
+    </p>
+    <p>
+      RECTIFIER.--(1) An apparatus for changing alternating current into
+      pulsating direct current. (2) Specifically in wireless (<i>a</i>) a
+      crystal or vacuum tube detector, and (<i>b</i>) a two-electrode vacuum
+      tube used for changing commercial alternating current into direct current
+      for wireless telephony.
+    </p>
+    <p>
+      REGENERATIVE AMPLIFICATION.--See <i>Amplification, Regenerative</i>.
+    </p>
+    <p>
+      RECEPTOR.--A receiving set.
+    </p>
+    <p>
+      RECEPTOR, AUTODYNE.--A receptor that has a regenerative circuit and the
+      same tube is used as a detector and as a generator of local oscillations.
+    </p>
+    <p>
+      RECEPTOR, BEAT.--A heterodyne receptor.
+    </p>
+    <p>
+      RECEPTOR, HETERODYNE.--A receiving set that uses a separate vacuum tube to
+      set up the second series of waves for beat reception.
+    </p>
+    <p>
+      REGENERATIVE ACTION.--See <i>Feed-Back Action.</i>
+    </p>
+    <p>
+      REGENERATIVE AMPLIFICATION.--See <i>Amplification, Regenerative.</i>
+    </p>
+    <p>
+      RELAY, ELECTRON.--A vacuum tube when used as a detector or an amplifier.
+    </p>
+    <p>
+      REPEATING COIL.--A transformer used in connecting up a wireless receiver
+      with a wire transmitter.
+    </p>
+    <p>
+      RESISTANCE.--The opposition offered by a wire or other conductor to the
+      passage of a current.
+    </p>
+    <p>
+      RESISTANCE, AERIAL.--The resistance of the aerial wire to oscillating
+      currents. This is greater than its ordinary ohmic resistance due to the
+      skin effect. See <i>Resistance, High Frequency.</i>
+    </p>
+    <p>
+      RESISTANCE BOX.--See <i>Resistor.</i>
+    </p>
+    <p>
+      RESISTANCE COUPLING.--See <i>Coupling, Resistance.</i>
+    </p>
+    <p>
+      RESISTANCE, HIGH FREQUENCY.--When a high frequency current oscillates on a
+      wire two things take place that are different than when a direct or
+      alternating current flows through it, and these are (1) the current inside
+      of the wire lags behind that of the current on the surface, and (2) the
+      amplitude of the current is largest on the surface and grows smaller as
+      the center of the wire is reached. This uneven distribution of the current
+      is known as the <i>skin effect</i> and it amounts to the same thing as
+      reducing the size of the wire, hence the resistance is increased.
+    </p>
+    <p>
+      RESISTIVITY.--The resistance of a given length of wire of uniform cross
+      section. The reciprocal of <i>conductivity.</i>
+    </p>
+    <p>
+      RESISTOR.--A fixed or variable resistance unit or a group of such units.
+      Variable resistors are also called <i>resistance boxes</i> and more often
+      <i>rheostats.</i>
+    </p>
+    <p>
+      RESONANCE.--(1) Simple resonance of sound is its increase set up by one
+      body by the sympathetic vibration of a second body. (2) By extension the
+      increase in the amplitude of electric oscillations when the circuit in
+      which they surge has a <i>natural</i> period that is the same, or nearly
+      the same, as the period of the first oscillation circuit.
+    </p>
+    <p>
+      RHEOSTAT.--A variable resistance unit. See <i>Resistor.</i>
+    </p>
+    <p>
+      RHEOSTAT, CARBON.--A carbon rod, or carbon plates or blocks, when used as
+      variable resistances.
+    </p>
+    <p>
+      RHEOSTAT, FILAMENT.--A variable resistance used for keeping the current of
+      the storage battery which heats the filament of a vacuum tube at a
+      constant voltage.
+    </p>
+    <p>
+      ROTATING COIL.--See <i>Coil.</i>
+    </p>
+    <p>
+      ROTARY GAP.--See <i>Gap.</i>
+    </p>
+    <p>
+      ROTOR.--The rotating coil of a variometer or a variocoupler.
+    </p>
+    <p>
+      RUHMKORFF COIL.--See <i>Coil, Induction.</i>
+    </p>
+    <p>
+      SATURATION.--The maximum plate current that a vacuum tube will take.
+    </p>
+    <p>
+      SENSITIVE SPOTS.--Spots on detector crystals that are sensitive to the
+      action of electric oscillations.
+    </p>
+    <p>
+      SHORT WAVES.--See <i>Waves.</i>
+    </p>
+    <p>
+      SIDE WAVES.--See <i>Wave Length Band.</i>
+    </p>
+    <p>
+      SIGNALS, CONVENTIONAL.--(1) The International Morse alphabet and numeral
+      code, punctuation marks, and a few important abbreviations used in
+      wireless telegraphy. (2) Dot and dash signals for distress call,
+      invitation to transmit, etc. Now used for all general public service
+      wireless communication.
+    </p>
+    <p>
+      SKIN EFFECT.--See <i>Resistance, High Frequency.</i>
+    </p>
+    <p>
+      SOFT TUBE.--A vacuum tube in which the vacuum is low, that is, it is not
+      highly exhausted.
+    </p>
+    <p>
+      SPACE CHARGE EFFECT.--The electric field intensity due to the pressure of
+      the negative electrons in the space between the filament and plate which
+      at last equals and neutralizes that due to the positive potential of the
+      plate so that there is no force acting on the electrons near the filament.
+    </p>
+    <p>
+      SPARK.--See <i>Discharge.</i>
+    </p>
+    <p>
+      SPARK COIL.--See <i>Coil, Induction.</i>
+    </p>
+    <p>
+      SPARK DISCHARGE.--See <i>Spark, Electric.</i>
+    </p>
+    <p>
+      SPARK FREQUENCY.--See <i>Frequency, Spark.</i>
+    </p>
+    <p>
+      SPARK GAP.--(1) A <i>spark gap,</i> without the hyphen, means the
+      apparatus in which sparks take place; it is also called a <i>spark
+      discharger.</i> (2) <i>Spark-gap,</i> with the hyphen, means the air-gap
+      between the opposed faces of the electrodes in which sparks are produced.
+    </p>
+    <ul>
+      <li>
+        <i>Plain.--</i>A spark gap with fixed electrodes.
+      </li>
+      <li>
+        <i>Rotary.--</i>A spark gap with a pair of fixed electrodes and a number
+        of electrodes mounted on a rotating element.
+      </li>
+      <li>
+        <i>Quenched.--</i>A spark gap formed of a number of metal plates placed
+        closely together and insulated from each other.
+      </li>
+    </ul>
+    <p>
+      SPIDER WEB INDUCTANCE COIL.--See <i>Coil, Spider Web Inductance.</i>
+    </p>
+    <p>
+      SPREADER.--A stick of wood, or spar, that holds the wires of the aerial
+      apart.
+    </p>
+    <p>
+      STAGGER WOUND COILS.--See <i>Coils, Inductance.</i>
+    </p>
+    <p>
+      STAND-BY CIRCUITS.--See <i>Circuits, Stand-By.</i>
+    </p>
+    <p>
+      STATIC.--Also called <i>atmospherics, grinders, strays, X's,</i> and, when
+      bad enough, by other names. It is an electrical disturbance in the
+      atmosphere which makes noises in the telephone receiver.
+    </p>
+    <p>
+      STATOR.--The fixed or stationary coil of a variometer or a variocoupler.
+    </p>
+    <p>
+      STORAGE BATTERY.--See <i>Battery, Storage.</i>
+    </p>
+    <p>
+      STRAY ELIMINATION.--A method for increasing the strength of the signals as
+      against the strength of the strays. See <i>Static.</i>
+    </p>
+    <p>
+      STRAYS.--See <i>Static</i>.
+    </p>
+    <p>
+      STRANDED WIRE.--See <i>Wire, Stranded</i>.
+    </p>
+    <p>
+      SUPER-HETERODYNE RECEPTOR.--See <i>Heterodyne, Super</i>.
+    </p>
+    <p>
+      SWINGING.--See <i>Fading</i>.
+    </p>
+    <p>
+      SWITCH, AERIAL.--A switch used to change over from the sending to the
+      receiving set, and the other way about, and connect them with the aerial.
+    </p>
+    <p>
+      SWITCH, LIGHTNING.--The switch that connects the aerial with the outside
+      ground when the apparatus is not in use.
+    </p>
+    <p>
+      SYMBOLS, APPARATUS.--Also called <i>conventional symbols</i>. These are
+      diagrammatic lines representing various parts of apparatus so that when a
+      wiring diagram of a transmitter or a receptor is to be made it is only
+      necessary to connect them together. They are easy to make and easy to
+      read. See <i>Page 307</i> [Appendix: Symbols Used for Apparatus].
+    </p>
+    <p>
+      SYNCHRONOUS GAP.--See <i>Gap, Synchronous</i>.
+    </p>
+    <p>
+      TELEPHONY, LINE RADIO.--See <i>Wired Wireless</i>.
+    </p>
+    <p>
+      THERMAL AMMETER.--See <i>Ammeter, Hot Wire</i>.
+    </p>
+    <p>
+      THREE ELECTRODE VACUUM TUBE.--<i>See Vacuum Tube, Three Electrode</i>.
+    </p>
+    <p>
+      TIKKER.--A slipping contact device that breaks up the sustained
+      oscillations at the receiving end into groups so that the signals can be
+      heard in the head phones. The device usually consists of a fine steel or
+      gold wire slipping in the smooth groove of a rotating brass wheel.
+    </p>
+    <p>
+      TRANSFORMER.--A primary and a secondary coil for stepping up or down a
+      primary alternating or oscillating current.
+    </p>
+    <ul>
+      <li>
+        <i>A. C.</i>--See <i>Power Transformer</i>.
+      </li>
+      <li>
+        <i>Air Cooled</i>.--A transformer in which the coils are exposed to the
+        air.
+      </li>
+      <li>
+        <i>Air Core</i>.--With high frequency currents it is the general
+        practice not to use iron cores as these tend to choke off the
+        oscillations. Hence the core consists of the air inside of the coils.
+      </li>
+      <li>
+        <i>Auto.--</i>A single coil of wire in which one part forms the primary
+        and the other part the secondary by bringing out an intermediate tap.
+      </li>
+      <li>
+        <i>Audio Amplifying.--</i>This is a transformer with an iron core and is
+        used for frequencies up to say 3,000.
+      </li>
+      <li>
+        <i>Closed Core.--</i>A transformer in which the path of the magnetic
+        flux is entirely through iron. Power transformers have closed cores.
+      </li>
+      <li>
+        <i>Microphone.--</i>A small transformer for modulating the oscillations
+        set up by an arc or a vacuum tube oscillator.
+      </li>
+      <li>
+        <i>Oil Cooled.--</i>A transformer in which the coils are immersed in
+        oil.
+      </li>
+      <li>
+        <i>Open Core.--</i>A transformer in which the path of the magnetic flux
+        is partly through iron and partly through air. Induction coils have open
+        cores.
+      </li>
+      <li>
+        <i>Oscillation.--</i>A coil or coils for transforming or stepping down
+        or up oscillating currents. Oscillation transformers usually have no
+        iron cores when they are also called <i>air core transformers.</i>
+      </li>
+      <li>
+        <i>Power.--</i>A transformer for stepping down a commercial alternating
+        current for lighting and heating the filament and for stepping up the
+        commercial a.c., for charging the plate of a vacuum tube oscillator.
+      </li>
+      <li>
+        <i>Radio Amplifying.--</i>This is a transformer with an air core. It
+        does not in itself amplify but is so called because it is used in
+        connection with an amplifying tube.
+      </li>
+    </ul>
+    <p>
+      TRANSMITTER, MICROPHONE.--A telephone transmitter of the kind that is used
+      in the Bell telephone system.
+    </p>
+    <p>
+      TRANSMITTING TUNING COILS.--See <i>Coils, Inductance.</i>
+    </p>
+    <p>
+      TUNING.--When the open and closed oscillation circuits of a transmitter or
+      a receptor are adjusted so that both of the former will permit electric
+      oscillations to surge through them with the same frequency, they are said
+      to be tuned. Likewise, when the sending and receiving stations are
+      adjusted to the same wave length they are said to be <i>tuned.</i>
+    </p>
+    <ul>
+      <li>
+        <i>Coarse Tuning.--</i>The first adjustment in the tuning oscillation
+        circuits of a receptor is made with the inductance coil and this tunes
+        them coarse, or roughly.
+      </li>
+      <li>
+        <i>Fine Tuning.--</i>After the oscillation circuits have been roughly
+        tuned with the inductance coil the exact adjustment is obtained with the
+        variable condenser and this is <i>fine tuning.</i>
+      </li>
+      <li>
+        <i>Sharp.--</i>When a sending set will transmit or a receiving set will
+        receive a wave of given length only it is said to be sharply tuned. The
+        smaller the decrement the sharper the tuning.
+      </li>
+    </ul>
+    <p>
+      TUNING COILS.--See <i>Coils, Inductance.</i>
+    </p>
+    <p>
+      TWO ELECTRODE VACUUM TUBE.--See <i>Vacuum Tube, Two Electrode.</i>
+    </p>
+    <p>
+      VACUUM TUBE.--A tube with two or three electrodes from which the air has
+      been exhausted, or which is filled with an inert gas, and used as a
+      detector, an amplifier, an oscillator or a modulator in wireless
+      telegraphy and telephony.
+    </p>
+    <ul>
+      <li>
+        <i>Amplifier.--</i>See <i>Amplifier, Vacuum Tube.</i>
+      </li>
+      <li>
+        <i>Amplifying Modulator.--</i>A vacuum tube used for modulating and
+        amplifying the oscillations set up by the sending set.
+      </li>
+      <li>
+        <i>Gas Content.--</i>A tube made like a vacuum tube and used as a
+        detector but which contains an inert gas instead of being exhausted.
+      </li>
+      <li>
+        <i>Hard.--</i>See <i>Hard Tube.</i>
+      </li>
+      <li>
+        <i>Rectifier.--</i>(1) A vacuum tube detector. (2) a two-electrode
+        vacuum tube used for changing commercial alternating current into direct
+        current for wireless telephony.
+      </li>
+      <li>
+        <i>Soft.--</i>See <i>Soft Tube.</i>
+      </li>
+      <li>
+        <i>Three Electrode.--</i>A vacuum tube with three electrodes, namely a
+        filament, a grid and a plate.
+      </li>
+      <li>
+        <i>Two Electrode.--</i>A vacuum tube with two electrodes, namely the
+        filament and the plate.
+      </li>
+    </ul>
+    <p>
+      VALVE.--See <i>Vacuum Tube.</i>
+    </p>
+    <p>
+      VALVE, FLEMING.--See <i>Fleming Valve.</i>
+    </p>
+    <p>
+      VARIABLE CONDENSER.--See <i>Condenser, Variable.</i>
+    </p>
+    <p>
+      VARIABLE INDUCTANCE.--See <i>Inductance, Variable.</i>
+    </p>
+    <p>
+      VARIABLE RESISTANCE.--See <i>Resistance, Variable.</i>
+    </p>
+    <p>
+      VARIOCOUPLER.--A tuning device for varying the inductance of the receiving
+      oscillation circuits. It consists of a fixed and a rotatable coil whose
+      windings are not connected with each other.
+    </p>
+    <p>
+      VARIOMETER.--A tuning device for varying the inductance of the receiving
+      oscillation currents. It consists of a fixed and a rotatable coil with the
+      coils connected in series.
+    </p>
+    <p>
+      VERNIER CONDENSER.--See <i>Condenser, Vernier.</i>
+    </p>
+    <p>
+      VOLT.--The electromotive force which produces a current of 1 ampere when
+      steadily applied to a conductor the resistance of which is one ohm.
+    </p>
+    <p>
+      VOLTAGE DIVIDER.--See <i>Potentiometer.</i>
+    </p>
+    <p>
+      VOLTAGE, PLATE.--The voltage of the current that is used to energize the
+      plate of a vacuum tube.
+    </p>
+    <p>
+      VOLTMETER.--An instrument for measuring the voltage of an electric
+      current.
+    </p>
+    <p>
+      WATCH CASE RECEIVER.--See <i>Receiver, Watch Case.</i>
+    </p>
+    <p>
+      WATER-PIPE GROUND.--See <i>Ground, Water-Pipe.</i>
+    </p>
+    <p>
+      WATT.--The power spent by a current of 1 ampere in a resistance of 1 ohm.
+    </p>
+    <p>
+      WAVE, BROAD.--A wave having a high decrement, when the strength of the
+      signals is nearly the same over a wide range of wave lengths.
+    </p>
+    <p>
+      WAVE LENGTH.--Every wave of whatever kind has a length. The wave length is
+      usually taken to mean the distance between the crests of two successive
+      waves.
+    </p>
+    <p>
+      WAVE LENGTH BAND.--In wireless reception when continuous waves are being
+      sent out and these are modulated by a microphone transmitter the different
+      audio frequencies set up corresponding radio frequencies and the energy of
+      these are emitted by the aerial; this results in waves of different
+      lengths, or a band of waves as it is called.
+    </p>
+    <p>
+      WAVE METER.--An apparatus for measuring the lengths of electric waves set
+      up in the oscillation circuits of sending and receiving sets.
+    </p>
+    <p>
+      WAVE MOTION.--Disturbances set up in the surrounding medium as water waves
+      in and on the water, sound waves in the air and electric waves in the
+      ether.
+    </p>
+    <p>
+      WAVES.--See <i>Wave Motion</i>.
+    </p>
+    <p>
+      WAVES, ELECTRIC.--Electromagnetic waves set up in and transmitted by and
+      through the ether.
+    </p>
+    <ul>
+      <li>
+        <i>Continuous</i>. <i>Abbreviated C.W.</i>--Waves that are emitted
+        without a break from the aerial. Also called <i>undamped waves</i>.
+      </li>
+      <li>
+        <i>Discontinuous</i>.--Waves that are emitted periodically from the
+        aerial. Also called <i>damped waves</i>. <i>Damped</i>.--See <i>Discontinuous
+        Waves</i>.
+      </li>
+      <li>
+        <i>Intermediate</i>.--Waves from 600 to 2,000 meters in length.
+      </li>
+      <li>
+        <i>Long</i>.--Waves over 2,000 meters in length. <i>Radio</i>.--Electric
+        waves used in wireless telegraphy and telephony.
+      </li>
+      <li>
+        <i>Short</i>.--Waves up to 600 meters in length.
+      </li>
+      <li>
+        <i>Wireless</i>.--Electric waves used in wireless telegraphy and
+        telephony.
+      </li>
+      <li>
+        <i>Undamped</i>.--See <i>Continuous Waves</i>.
+      </li>
+    </ul>
+    <p>
+      WIRELESS TELEGRAPH CODE.--See <i>Code, International</i>.
+    </p>
+    <p>
+      WIRE, ENAMELLED.--Wire that is given a thin coat of enamel which insulates
+      it.
+    </p>
+    <p>
+      WIRE, PHOSPHOR BRONZE.--A very strong wire made of an alloy of copper and
+      containing a trace of phosphorus.
+    </p>
+    <p>
+      WIRED WIRELESS.--Continuous waves of high frequency that are sent over
+      telephone wires instead of through space. Also called <i>line radio
+      communication; carrier frequency telephony, carrier current telephony;
+      guided wave telephony</i> and <i>wired wireless.</i>
+    </p>
+    <p>
+      X'S.--See <i>Static.</i>
+    </p>
+    <p>
+      ZINCITE.--See <i>Detector.</i>
+    </p>
+    <h2>
+      <a name="donts" id="donts">WIRELESS DON'TS</a>
+    </h2>
+    <h3>
+      AERIAL WIRE DON'TS
+    </h3>
+    <p>
+      <i>Don't</i> use iron wire for your aerial.
+    </p>
+    <p>
+      <i>Don't</i> fail to insulate it well at both ends.
+    </p>
+    <p>
+      <i>Don't</i> have it longer than 75 feet for sending out a 200-meter wave.
+    </p>
+    <p>
+      <i>Don't</i> fail to use a lightning arrester, or better, a lightning
+      switch, for your receiving set.
+    </p>
+    <p>
+      <i>Don't</i> fail to use a lightning switch with your transmitting set.
+    </p>
+    <p>
+      <i>Don't</i> forget you must have an outside ground.
+    </p>
+    <p>
+      <i>Don't</i> fail to have the resistance of your aerial as small as
+      possible. Use stranded wire.
+    </p>
+    <p>
+      <i>Don't</i> fail to solder the leading-in wire to the aerial.
+    </p>
+    <p>
+      <i>Don't</i> fail to properly insulate the leading-in wire where it goes
+      through the window or wall.
+    </p>
+    <p>
+      <i>Don't</i> let your aerial or leading-in wire touch trees or other
+      objects.
+    </p>
+    <p>
+      <i>Don't</i> let your aerial come too close to overhead wires of any kind.
+    </p>
+    <p>
+      <i>Don't</i> run your aerial directly under, or over, or parallel with
+      electric light or other wires.
+    </p>
+    <p>
+      <i>Don't</i> fail to make a good ground connection with the water pipe
+      inside.
+    </p>
+    <h3>
+      TRANSMITTING DON'TS
+    </h3>
+    <p>
+      <i>Don't</i> attempt to send until you get your license.
+    </p>
+    <p>
+      <i>Don't</i> fail to live up to every rule and regulation.
+    </p>
+    <p>
+      <i>Don't</i> use an input of more than 1/2 a kilowatt if you live within 5
+      nautical miles of a naval station.
+    </p>
+    <p>
+      <i>Don't</i> send on more than a 200-meter wave if you have a restricted
+      or general amateur license.
+    </p>
+    <p>
+      <i>Don't</i> use spark gap electrodes that are too small or they will get
+      hot.
+    </p>
+    <p>
+      <i>Don't</i> use too long or too short a spark gap. The right length can
+      be found by trying it out.
+    </p>
+    <p>
+      <i>Don't</i> fail to use a safety spark gap between the grid and the
+      filament terminals where the plate potential is above 2,000 volts.
+    </p>
+    <p>
+      <i>Don't</i> buy a motor-generator set if you have commercial alternating
+      current in your home.
+    </p>
+    <p>
+      <i>Don't</i> overload an oscillation vacuum tube as it will greatly
+      shorten its life. Use two in parallel.
+    </p>
+    <p>
+      <i>Don't</i> operate a transmitting set without a hot-wire ammeter in the
+      aerial.
+    </p>
+    <p>
+      <i>Don't</i> use solid wire for connecting up the parts of transmitters.
+      Use stranded or braided wire.
+    </p>
+    <p>
+      <i>Don't</i> fail to solder each connection.
+    </p>
+    <p>
+      <i>Don't</i> use soldering fluid, use rosin.
+    </p>
+    <p>
+      <i>Don't</i> think that all of the energy of an oscillation tube cannot be
+      used for wave lengths of 200 meters and under. It can be if the
+      transmitting set and aerial are properly designed.
+    </p>
+    <p>
+      <i>Don't</i> run the wires of oscillation circuits too close together.
+    </p>
+    <p>
+      <i>Don't</i> cross the wires of oscillation circuits except at right
+      angles.
+    </p>
+    <p>
+      <i>Don't</i> set the transformer of a transmitting set nearer than 3 feet
+      to the condenser and tuning coil.
+    </p>
+    <p>
+      <i>Don't</i> use a rotary gap in which the wheel runs out of true.
+    </p>
+    <h3>
+      RECEIVING DON'TS
+    </h3>
+    <p>
+      <i>Don't</i> expect to get as good results with a crystal detector as with
+      a vacuum tube detector.
+    </p>
+    <p>
+      <i>Don't</i> be discouraged if you fail to hit the sensitive spot of a
+      crystal detector the first time--or several times thereafter.
+    </p>
+    <p>
+      <i>Don't</i> use a wire larger than <i>No. 80</i> for the wire electrode
+      of a crystal detector.
+    </p>
+    <p>
+      <i>Don't</i> try to use a loud speaker with a crystal detector receiving
+      set.
+    </p>
+    <p>
+      <i>Don't</i> expect a loop aerial to give worthwhile results with a
+      crystal detector.
+    </p>
+    <p>
+      <i>Don't</i> handle crystals with your fingers as this destroys their
+      sensitivity. Use tweezers or a cloth.
+    </p>
+    <p>
+      <i>Don't</i> imbed the crystal in solder as the heat destroys its
+      sensitivity. Use <i>Wood's metal,</i> or some other alloy which melts at
+      or near the temperature of boiling water.
+    </p>
+    <p>
+      <i>Don't</i> forget that strong static and strong signals sometimes
+      destroy the sensitivity of crystals.
+    </p>
+    <p>
+      <i>Don't</i> heat the filament of a vacuum tube to greater brilliancy than
+      is necessary to secure the sensitiveness required.
+    </p>
+    <p>
+      <i>Don't</i> use a plate voltage that is less or more than it is rated
+      for.
+    </p>
+    <p>
+      <i>Don't</i> connect the filament to a lighting circuit.
+    </p>
+    <p>
+      <i>Don't</i> use dry cells for heating the filament except in a pinch.
+    </p>
+    <p>
+      <i>Don't</i> use a constant current to heat the filament, use a constant
+      voltage.
+    </p>
+    <p>
+      <i>Don't</i> use a vacuum tube in a horizontal position unless it is made
+      to be so used.
+    </p>
+    <p>
+      <i>Don't</i> fail to properly insulate the grid and plate leads.
+    </p>
+    <p>
+      <i>Don't</i> use more than 1/3 of the rated voltage on the filament and on
+      the plate when trying it out for the first time.
+    </p>
+    <p>
+      <i>Don't</i> fail to use alternating current for heating the filament
+      where this is possible.
+    </p>
+    <p>
+      <i>Don't</i> fail to use a voltmeter to find the proper temperature of the
+      filament.
+    </p>
+    <p>
+      <i>Don't</i> expect to get results with a loud speaker when using a single
+      vacuum tube.
+    </p>
+    <p>
+      <i>Don't</i> fail to protect your vacuum tubes from mechanical shocks and
+      vibration.
+    </p>
+    <p>
+      <i>Don't</i> fail to cut off the <i>A</i> battery entirely from the
+      filament when you are through receiving.
+    </p>
+    <p>
+      <i>Don't</i> switch on the <i>A</i> battery current all at once through
+      the filament when you start to receive.
+    </p>
+    <p>
+      <i>Don't</i> expect to get the best results with a gas-content detector
+      tube without using a potentiometer.
+    </p>
+    <p>
+      <i>Don't</i> connect a potentiometer across the <i>B</i> battery or it
+      will speedily run down.
+    </p>
+    <p>
+      <i>Don't</i> expect to get as good results with a single coil tuner as you
+      would with a loose coupler.
+    </p>
+    <p>
+      <i>Don't</i> expect to get as good results with a two-coil tuner as with
+      one having a third, or <i>tickler</i>, coil.
+    </p>
+    <p>
+      <i>Don't</i> think you have to use a regenerative circuit, that is, one
+      with a tickler coil, to receive with a vacuum tube detector.
+    </p>
+    <p>
+      <i>Don't</i> think you are the only amateur who is troubled with static.
+    </p>
+    <p>
+      <i>Don't</i> expect to eliminate interference if the amateurs around you
+      are sending with spark sets.
+    </p>
+    <p>
+      <i>Don't</i> lay out or assemble your set on a panel first. Connect it up
+      on a board and find out if everything is right.
+    </p>
+    <p>
+      <i>Don't</i> try to connect up your set without a wiring diagram in front
+      of you.
+    </p>
+    <p>
+      <i>Don't</i> fail to shield radio frequency amplifiers.
+    </p>
+    <p>
+      <i>Don't</i> set the axes of the cores of radio frequency transformers in
+      a line. Set them at right angles to each other.
+    </p>
+    <p>
+      <i>Don't</i> use wire smaller than <i>No. 14</i> for connecting up the
+      various parts.
+    </p>
+    <p>
+      <i>Don't</i> fail to adjust the <i>B</i> battery after putting in a fresh
+      vacuum tube, as its sensitivity depends largely on the voltage.
+    </p>
+    <p>
+      <i>Don't</i> fail to properly space the parts where you use variometers.
+    </p>
+    <p>
+      <i>Don't</i> fail to put a copper shield between the variometer and the
+      variocoupler.
+    </p>
+    <p>
+      <i>Don't</i> fail to keep the leads to the vacuum tube as short as
+      possible.
+    </p>
+    <p>
+      <i>Don't</i> throw your receiving set out of the window if it <i>howls</i>.
+      Try placing the audio-frequency transformers farther apart and the cores
+      of them at right angles to each other.
+    </p>
+    <p>
+      <i>Don't</i> use condensers with paper dielectrics for an amplifier
+      receiving set or it will be noisy.
+    </p>
+    <p>
+      <i>Don't</i> expect as good results with a loop aerial, or when? using the
+      bed springs, as an out-door aerial will give you.
+    </p>
+    <p>
+      <i>Don't</i> use an amplifier having a plate potential of less than 100
+      volts for the last step where a loud speaker is to be used.
+    </p>
+    <p>
+      <i>Don't</i> try to assemble a set if you don't know the difference
+      between a binding post and a blue print. Buy a set ready to use.
+    </p>
+    <p>
+      <i>Don't</i> expect to get Arlington time signals and the big cableless
+      stations if your receiver is made for short wave lengths.
+    </p>
+    <p>
+      <i>Don't</i> take your headphones apart. You are just as apt to spoil them
+      as you would a watch.
+    </p>
+    <p>
+      <i>Don't</i> expect to get results with a Bell telephone receiver.
+    </p>
+    <p>
+      <i>Don't</i> forget that there are other operators using the ether besides
+      yourself.
+    </p>
+    <p>
+      <i>Don't</i> let your <i>B</i> battery get damp and don't let it freeze.
+    </p>
+    <p>
+      <i>Don't</i> try to recharge your <i>B</i> battery unless it is
+      constructed for the purpose.
+    </p>
+    <h3>
+      STORAGE BATTERY DON'TS
+    </h3>
+    <p>
+      <i>Don't</i> connect a source of alternating current direct to your
+      storage battery. You have to use a rectifier.
+    </p>
+    <p>
+      <i>Don't</i> connect the positive lead of the charging circuit with the
+      negative terminal of your storage battery.
+    </p>
+    <p>
+      <i>Don't</i> let the electrolyte get lower than the tops of the plates of
+      your storage battery.
+    </p>
+    <p>
+      <i>Don't</i> fail to look after the condition of your storage battery once
+      in a while.
+    </p>
+    <p>
+      <i>Don't</i> buy a storage battery that gives less than 6 volts for
+      heating the filament.
+    </p>
+    <p>
+      <i>Don't</i> fail to keep the specific gravity of the electrolyte of your
+      storage battery between 1.225 and 1.300 Baume. This you can do with a
+      hydrometer.
+    </p>
+    <p>
+      <i>Don't</i> fail to recharge your storage battery when the hydrometer
+      shows that the specific gravity of the electrolyte is close to 1.225.
+    </p>
+    <p>
+      <i>Don't</i> keep charging the battery after the hydrometer shows that the
+      specific gravity is 1.285.
+    </p>
+    <p>
+      <i>Don't</i> let the storage battery freeze.
+    </p>
+    <p>
+      <i>Don't</i> let it stand for longer than a month without using unless you
+      charge it.
+    </p>
+    <p>
+      <i>Don't</i> monkey with the storage battery except to add a little
+      sulphuric acid to the electrolyte from time to time. If anything goes
+      wrong with it better take it to a service station and let the expert do
+      it.
+    </p>
+    <h3>
+      EXTRA DON'TS
+    </h3>
+    <p>
+      <i>Don't</i> think you have an up-to-date transmitting station unless you
+      are using C.W.
+    </p>
+    <p>
+      <i>Don't</i> use a wire from your lightning switch down to the outside
+      ground that is smaller than No. <i>4</i>.
+    </p>
+    <p>
+      <i>Don't</i> try to operate your spark coil with 110-volt direct lighting
+      current without connecting in a rheostat.
+    </p>
+    <p>
+      <i>Don't</i> try to operate your spark coil with 110-volt alternating
+      lighting current without connecting in an electrolytic interrupter.
+    </p>
+    <p>
+      <i>Don't</i> try to operate an alternating current power transformer with
+      110-volt direct current without connecting in an electrolytic interruptor.
+    </p>
+    <p>
+      <i>Don't</i>--no never--connect one side of the spark gap to the aerial
+      wire and the other side of the spark gap to the ground. The Government
+      won't have it--that's all.
+    </p>
+    <p>
+      <i>Don't</i> try to tune your transmitter to send out waves of given
+      length by guesswork. Use a wavemeter.
+    </p>
+    <p>
+      <i>Don't</i> use <i>hard fiber</i> for panels. It is a very poor insulator
+      where high frequency currents are used.
+    </p>
+    <p>
+      <i>Don't</i> think you are the only one who doesn't know all about
+      wireless. Wireless is a very complex art and there are many things that
+      those experienced have still to learn.
+    </p>
+    <h3>
+      THE END.
+    </h3>
+    <p>
+      <br /> <br /> <br /> <br />
+    </p>
+<pre xml:space="preserve">
+*** END OF THE PROJECT GUTENBERG EBOOK, THE RADIO AMATEUR'S HAND BOOK ***
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author	Roger Frank <rfrank@pglaf.org>	2025-10-15 05:28:33 -0700
committer	Roger Frank <rfrank@pglaf.org>	2025-10-15 05:28:33 -0700
commit	3a6de40b7e0ea6335d60c985c2d54d7b9f5afced (patch)
tree	0a0025aee62abb53d46650621e6877a8c5a0031d /6935-h