diff options
Diffstat (limited to '63207-0.txt')
| -rw-r--r-- | 63207-0.txt | 9739 |
1 files changed, 9739 insertions, 0 deletions
diff --git a/63207-0.txt b/63207-0.txt new file mode 100644 index 0000000..126f524 --- /dev/null +++ b/63207-0.txt @@ -0,0 +1,9739 @@ + The Boy Electrician + + + + +This ebook is for the use of anyone anywhere in the United States and +most other parts of the world at no cost and with almost no restrictions +whatsoever. You may copy it, give it away or re-use it under the terms +of the Project Gutenberg License included with this ebook or online at +https://www.gutenberg.org/license. If you are not located in the United +States, you’ll have to check the laws of the country where you are +located before using this ebook. + + + +Title: The Boy Electrician +Author: Alfred Powell Morgan +Release Date: September 15, 2020 [EBook #63207] +Language: English +Character set encoding: UTF-8 + + +*** START OF THIS PROJECT GUTENBERG EBOOK THE BOY ELECTRICIAN *** + + + + +Produced by James Simmons. + +This file was produced from page images at Google Books. + + + + +Transcriber’s Note + + +This book was transcribed from scans of the original found at Google +Books. I have rotated some images. The more complex tables are treated +as images. + + + + +[Illustration: A BOY’S WIRELESS OUTFIT MADE UP OF THE APPARATUS +DESCRIBED IN CHAPTER XIV. THE JUNIOR DYNAMO AND A COHERER OUTFIT CAN BE +SEEN ON THE LOWER PART OF THE TABLE.] + + + + + The + + Boy + + Electrician + + + _Practical Plans for Electrical_ + + _Apparatus for work and play, with an explanation_ + + _Of the principles of every-day electricity._ + + + By + + ALFRED P MORGAN + + + _With illustrations by the author_ + + + + + BOSTON + + LOTHROP, LEE & SHEPARD CO. + + + + + Copyright, 1913, by Lothrop, Lee & Shepard Co. + + Entered at Stationers’ Hall, London + + Published July, 1914 + + _All rights reserved_ + + THE BOY ELECTRICIAN + + + + + NORWOOD PRESS + + Berwick & Smith Co. + + Norwood, Mass. U.S.A. + + + + + TO THE SELF-RELIANT + + *BOYS OF AMERICA,* + + OUR FUTURE ENGINEERS AND SCIENTISTS, THAN WHOM + + NONE IN THE WHOLE WORLD ARE BETTER ABLE + + TO WORK OUT AND SOLVE THE PROBLEMS + + THAT EVER CONFRONT YOUNG + + MANHOOD, THIS BOOK + + IS CORDIALLY + + DEDICATED. + + + + +THE BOY ELECTRICIAN + + + +INTRODUCTION + + +Once upon a time, and this is a true tale, a boy had a whole railroad +system for a toy. The train ran automatically, propelled by tiny +electric motors, the signals went up and down, the station was reached, +a bell rang, the train moved on again and was off on its journey around +many feet of track to come back over the old route. + +The boy viewed his gift with raptured eyes, and then his face changed +and he cried out in the bitterness of his disappointment: "But what do I +do?" The toy was so elaborate that the boy was left entirely out of the +play. Of course he did not like it. His cry tells a long story. + +The prime instinct of almost any boy at play is to _make_ and to +_create_. He will _make_ things of such materials as he has at hand, and +use the whole force of dream and fancy to create something out of +nothing. The five-year-old will lay half a dozen wooden blocks together +with a spool on one end and tell you it is a steam train. And it is. He +has both made and created an engine, which he sees but which you don’t, +for the blocks and spool are only a symbol of his creation. Give his +older brother a telephone receiver, some wire and bits of brass, and he +will make a wireless telegraph outfit and listen to a steamship hundreds +of miles away spell out its message to the shore. + +The wireless outfit is not a symbol, but something that you can both +hear and see in operation even though you may not understand the +whispering of the dots and dashes. And as soon as the mystery of this +modern wonder more firmly grips your imagination, you perhaps may come +to realize that we are living more and more in the age of electricity +and mechanism. Electricity propels our trains, lights our houses and +streets, makes our clothes, cures our ills, warms us, cooks for us and +performs an innumerable number of other tasks at the turning of a little +switch. A mere list is impossible. + +Almost every boy experiments at one time or another with electricity and +electrical apparatus. It is my purpose in writing this book to open this +wonderland of science and present it in a manner which can be readily +understood, and wherein a boy may "do something." Of course there are +other books with the same purport, but they do not accomplish their end. +They are not practical. I can say this because as a boy I have read and +studied them and they have fallen far short of teaching me or my +companions the things that we were seeking to learn. If they have failed +in this respect, they have done so perhaps not through any inability of +the author, but from the fact that they have not been written from the +_boy’s standpoint_. They tell what the author _thought_ a boy ought to +know but not what he really does want to know. The apparatus described +therein is for the most part imaginary. The author thought it might be +possible for a boy to build motors, telegraph instruments, etc., out of +old bolts and tin cans, but _he never tried to do so himself_. + +The apparatus and experiments that I have described have been +constructed and carried out by _boys_. Their problems and their +questions have been studied and remedied. I have tried to present +practical matter considered wholly from a boy’s standpoint, and to show +the young experimenter just what he can do with the tools and materials +in his possession or not hard to obtain. + +To the boy interested in science, a wide field is open. There is no +better education for any boy than to begin at the bottom of the ladder +and climb the rungs of scientific knowledge, step by step. It equips him +with information which may prove of inestimable worth in an opportune +moment. + +There is an apt illustration in the boy who watched his mother empty a +jug of molasses into a bowl and replace the cork. His mother told him +not to disturb the jug, as it was empty. He persisted, however, and +turned the jug upside down. No more molasses came, but _out crawled a +fly_. New developments in science will never cease. Invention will +follow invention. The unexpected is often a valuable clue. The Edisons +and Teslas of to-day have not discovered everything. _There is a fly in +the molasses_, to be had by persistence. Inspiration is but a +starting-point. Success means work, days, nights, weeks, and years. + +There can be no boy who will follow exactly any directions given to him, +or do exactly as he is told, of his own free will. He will "bolt" at the +first opportunity. If forced or obliged to do as he is directed, his +action will be accompanied by many a "why?" Therefore in presenting the +following chapters I have not only told how to _make_ the various +motors, telegraphs, telephones, radio receivers, etc. but have also +explained the principles of electricity upon which they depend for their +operation, and how the same thing is accomplished in the every-day +world. In giving directions or offering cautions, I have usually stated +the reason for so doing, in the hope that this information may be a +stimulant to the imagination of the young experimenter and a useful +guide in enabling him to proceed along some of the strange roads on +which he will surely go. + +ALFRED P. MORGAN + +UPPER MONTCLAIR, N. J. + + + + + THE BOY ELECTRICIAN ............................................... + INTRODUCTION .................................................... + CHAPTER I MAGNETS AND MAGNETISM ................................. + CHAPTER II STATIC ELECTRICITY ................................... + CHAPTER III STATIC ELECTRIC MACHINES ............................ + CHAPTER IV CELLS AND BATTERIES .................................. + CHAPTER V ELECTRO-MAGNETISM AND MAGNETIC INDUCTION .............. + CHAPTER VI ELECTRICAL UNITS ..................................... + CHAPTER VII ELECTRICAL APPURTENANCES ............................ + CHAPTER VIII ELECTRICAL MEASURING INSTRUMENTS ................... + CHAPTER IX BELLS, ALARMS, AND ANNUNCIATORS ...................... + CHAPTER X ELECTRIC TELEGRAPHS ................................... + CHAPTER XI MICROPHONES AND TELEPHONES ........................... + CHAPTER XII INDUCTION COILS ..................................... + CHAPTER XIII TRANSFORMERS ....................................... + CHAPTER VIV WIRELESS TELEGRAPHY ................................. + CHAPTER XV A WIRELESS TELEPHONE ................................. + CHAPTER XVI ELECTRIC MOTORS ..................................... + CHAPTER XVII DYNAMOS ............................................ + CHAPTER XVIII AN ELECTRIC RAILWAY ............................... + CHAPTER XIX MINIATURE LIGHTING .................................. + CHAPTER XX MISCELLANEOUS ELECTRICAL APPARATUS ................... + The Full Project Gutenberg License ................................ + Section 1. General Terms of Use & Redistributing Project + Gutenberg™ electronic works ..................................... + Section 2. Information about the Mission of Project Gutenberg™ .. + Section 3. Information about the Project Gutenberg Literary + Archive Foundation .............................................. + Section 4. Information about Donations to the Project Gutenberg + Literary Archive Foundation ..................................... + Section 5. General Information About Project Gutenberg™ electronic + works. .......................................................... + + + + + A BOY’S WIRELESS OUTFIT MADE UP OF THE APPARATUS DESCRIBED IN + CHAPTER XIV. THE JUNIOR DYNAMO AND A COHERER OUTFIT CAN BE SEEN ON + THE LOWER PART OF THE TABLE. ...................................... + Fig. 1.—The Card of a Mariner’s Compass, Showing the "Points." .... + Fig. 2.—A Bar Magnet .............................................. + Fig. 3.—A Horseshoe Magnet ........................................ + Fig. 4.—A Magnetized Needle and a Bar Magnet which have been dipped + in Iron Filings. .................................................. + Fig. 5.—The Lifting Power of a Bar Magnet. _It must be brought + closer to the nails than the tacks because they are heavier_. ..... + Fig. 6.—A Simple Compass. ......................................... + Fig. 7.—Several Different Methods of Making a Simple Compass. ..... + Fig. 8.—The Attraction of an Iron Nail through _Glass_. ........... + Fig. 9.—A Magnetic Chain. ......................................... + Fig. 10.—An Experiment Illustrating that Like Poles Repel Each Other + and Unlike Poles Attract. ......................................... + Fig. 11.—A Magnetic Boat. ......................................... + Fig. 12.—Repulsion between Similar Poles, Shown by Floating Needles. + Fig. 13.—A Magnetic "Phantom," Showing the Field of Force about a + Magnet. ........................................................... + Fig. 14.—Magnetic Phantom showing the Lines of Force about a + Horseshoe Magnet. ................................................. + Fig. 15.—Lines of Force between Like and Unlike Poles. ............ + Fig. 16.—A Simple Dipping Needle. ................................. + Fig. 17.—An Electrified Glass Rod will Attract Small Bits of Paper. + _From the author’s "Wireless Telegraphy and Telephony" by + permission._ *A Double Lightning Discharge from a Cloud to the + Earth.* ........................................................... + Fig. 19.—A Piece of Dry Writing-Paper may be Electrified by Rubbing. + Fig. 20.—A Surprise for the Cat. .................................. + Fig. 21.—A Paper Electroscope. .................................... + Fig. 22.—A Pith-Ball Electroscope. ................................ + Fig. 23.—A Double Pith-Ball Electroscope. ......................... + Fig. 24.—A Gold-Leaf Electroscope. ................................ + Fig. 25.—Method of Suspending an Electrified Rod in a Wire Stirrup. + Fig. 26.—Similarly Electrified Bodies Repel Each Other. Dissimilarly + Electrified Ones Attract Each Other. .............................. + Fig. 27.—The Electrophorous ....................................... + Fig. 28.—An Electric Frog-Pond. ................................... + Fig. 29.—Front View of a Cylinder Electric Machine. ............... + Fig. 30.—Method of Finding the Center of a Circle. ................ + Fig. 31.—The "Rubber." ............................................ + Fig. 32.—The Prime Conductor or Collector. ........................ + Fig. 33.—The Complete Cylinder Electric Machine. .................. + Fig. 34.—Paper Pattern for laying out the Plates. ................. + Fig. 35.—Plate with Sectors in Position, and a Pattern for the + Sectors. .......................................................... + Fig. 36.—A Side View of one of the Bosses, showing the Brass Bushing + used. ............................................................. + Fig. 37.—The Frame. ............................................... + Fig. 38.—The Upright. ............................................. + Fig. 39.—The Driving-Wheels and Axle. ............................. + Fig. 40—The Boss and Axle. For sake of clearness, the Plate is not + shown. ............................................................ + Fig. 41—Showing how the Ball, Comb, etc., are mounted on the Glass + Rod. .............................................................. + Fig. 42.—A Comb or Collector. ..................................... + Fig. 43.—Showing how the Tinsel Brushes are arranged on the + "Neutralizer" Rods. ............................................... + Fig. 44.—The Complete Wimshurst Electric Machine. B B B B, + _Brushes_. C C, _Combs_. D B, _Discharge Ball_. I I, _Glass Rods_. + H, _Handle_. Q Q, _Quadrant Rods_. S S S S S, _Sectors_. S G, + _Spark-Gap_. P P, _Driving-Wheels_. For the sake of clearness, + several of the sectors are not shown. ............................. + Fig. 45.—The Leyden Jar. .......................................... + Fig. 46.—A Wooden Mortar for Igniting Gunpowder. .................. + Fig. 47.—An Electric Umbrella. .................................... + Fig. 48.—A Lightning Board. ....................................... + Fig. 49.—An Electric Dance. ....................................... + Fig. 50.—An Electric Whirl. ....................................... + Fig. 51.—Lichtenberg’s Figures. ................................... + Fig. 52.—The Voltaic Cell. ........................................ + Fig. 53.—The Elements of Simple Voltaic Cell. ..................... + Fig. 54.—A Home-Made Voltaic Cell. ................................ + Fig. 55.—Carbon-Cylinder Cell, and Cylinder. ...................... + Fig. 56.—A Leclanche Cell, showing the Porous Cup. ................ + Fig. 57.—A Dry Cell. .............................................. + Fig. 58.—The Different Operations involved in Making a Dry Cell. .. + Fig. 59.—A Zinc-Carbon Element, made from Heavy plates. ........... + Fig. 60.—A Method of making a Cell Element from Carbon Rods. ...... + Fig. 61. An Element made from two Carbon Plates and a Zinc Rod. ... + Fig. 62. A Method of Mounting four Carbon Plates. ................. + Fig. 63.—A Battery Element arranged for three Cells. .............. + Fig. 64.—A Plunge Battery, with Windlass. ......................... + Fig. 65.—A Plunge Battery adapted to a Set of Elements, as shown in + Figure 63. They may be lifted out and placed on the "Arms" to drain. + Fig. 66.—An Edison-Lalande Cell. .................................. + Fig. 67.—A Tomato-Can Cell; Sectional View. ....................... + Fig. 68.—The Tomato-Can Cell Complete. ............................ + Fig. 69.—Two Methods of Connecting Cells so as to obtain Different + Voltage and Amperage Values. ...................................... + Fig. 70.—Small Storage Cells. ..................................... + Fig. 71.—How to make the Plates for a Storage Cell. ............... + Fig. 72.—The Wood Separator. ...................................... + Fig. 73.—The Complete Element for a Storage Cell. ................. + Fig. 74.—A Battery of Home-Made Storage Cells. .................... + Fig. 75.—Gravity Cells. These consist of zinc and copper elements, + immersed in a zinc-copper sulphate solution. They cannot be easily + made, and are best purchased. The illustration also shows the + star-shaped copper and "crowfoot" zinc element used in a gravity + cell. ............................................................. + Fig. 76.—A Current of Electricity flowing through a Wire will + deflect a Compass Needle. ......................................... + Fig. 77.—If a Loop of Wire is formed about a Compass Needle, the + Deflection will be greater. ....................................... + Fig. 78.—Iron Filings clustered on a Wire carrying a Current of + Electricity. ...................................................... + Fig. 79.—Magnetic Phantom formed about a Wire carrying a Current of + Electricity. ...................................................... + Fig. 80.—Magnetic Phantom formed about several Turns of wire. ..... + Fig. 81.—Paper Tube wrapped with Wire for Experimental Purposes. .. + Fig. 82.—Showing how the Lines of Force "Leak" at the sides of the + coil, from a Coil of Wire, and how they are concentrated by an Iron + Core. ............................................................. + Fig. 83.—The Principle of an Electro-Magnet. ...................... + Fig. 84.—if you wrap some insulated Wire around an Ordinary Nail and + connect it to a Battery, it will become an Electro-Magnet. ........ + Fig. 85.—If you wind the Wire around a small Paper Tube into which a + Nail will slide easily, the Coil will draw the Nail in when the + Current is turned on. ............................................. + _By permission, from "Solenoids" by C. R. Underhill._ + Lifting-Magnets of the type known as Plate, Billet, and Ingot + Magnets. .......................................................... + Fig. 86.—Showing how a Current of Electricity may be induced by a + Bar Magnet and a Coil. ............................................ + Fig. 87.—A Horseshoe Magnet and a Coil arranged to produce Electric + Currents by _Induction_. .......................................... + Fig. 88.—Graphic Representation of a Direct and an Alternating + Current. .......................................................... + Fig. 89.—Staples and Wooden Cleat used for running Low Voltage + Wires. ............................................................ + Fig. 90.—Porcelain Insulators to support Electric Light Wires. .... + Fig. 91.—Glass Insulator Binding-Posts and Pin used to support + Telegraph and Telephone wires. .................................... + Fig. 92.—Types of Binding-Posts. .................................. + Fig. 93.—Home-made Binding-Posts. ................................. + Fig. 94.—Binding-Post removed from the Carbon of a Dry Cell. ...... + Fig. 95.—Simple Switches. _A_, Single-Point Switch. _B_, Two-Point + Switch. _C_, Three-Point Switch. _D_, Five-Point Switch. _E_, Lever + with End Rolled up to form Handle. _F_, Lever with Handle made from + part of a Spool. .................................................. + Fig. 96.—Knife Switches. .......................................... + Fig. 97.—Metal Parts for the Knife Switches. ...................... + Fig. 98.—Simple Fuses. _A_, Fuse-Block with plain Wire Fuse. _D_, + Fuse-Block with Mica Fuse in position. ............................ + Fig. 99.—Lightning-Arrester and Ground-Wire Switch. ............... + Fig. 100.—Home-made Lightning-Arrester. ........................... + Fig. 101.—Lightning-Arrester for Telephone Wires. ................. + Fig. 102.—_A_, Base, showing Slot. _B_ and _C_, Sides and Top of the + Bobbin. _D_, Base and Bobbin in Position. ......................... + Fig. 103.—Arrangement of the Needle and Pointer. .................. + Fig. 104.—_A_, Bearings. _B_, How the Needle is mounted. .......... + Fig. 105.—The Completed Meter. .................................... + Fig. 106.—Details of the Bobbin. .................................. + Fig. 107.—The Bobbin partly cut away so as to show the Bearing. + Details of the Armature and Shaft. ................................ + Fig. 108.—Completed Voltmeter. .................................... + Fig. 109.—Circuits for Calibrating the Ammeter and Voltmeter. ..... + Fig. 110.—Simple Compass Galvanoscope. ............................ + Fig. 111.—Galvanoscope. ........................................... + Fig. 112.—Astatic Galvanoscope. ................................... + Fig. 113.—Astatic Needles. ........................................ + Fig. 114.—Bobbin for Astatic Galvanometer. ........................ + Fig. 115.—Completed Astatic Galvanometer. ......................... + Fig. 116.—Wheatstone Bridge. ...................................... + Fig. 117.—Knife-Contact. .......................................... + Fig. 118.—Resistance-Coil. _A_ shows how the Wire is doubled and + wound on the Spool. _B_ is the completed Coil. .................... + Fig. 119.—Details of the Magnet Spools, and Yoke for an Electric + Bell. ............................................................. + Fig. 120.—Details of the Armature, and Contact Screw. ............. + Fig. 121.—The Completed Bell. ..................................... + Fig. 122.—Diagram showing how to connect a Bell, Battery, and + Push-Button. ...................................................... + Fig. 123.—Two Simple Push-Buttons. ................................ + Fig. 124.—Diagram showing how to arrange a Bell System of Return + Signals. .......................................................... + Fig. 125.—Burglar-Alarm Trap. ..................................... + Fig. 126.—An Early-Riser’s Electric Alarm Attachment for a Clock. . + Fig. 127.—Details of the Chain Electrodes, etc. ................... + Fig. 128.—An Annunciator Drop. .................................... + Fig 129.—Details of the Drop-Frame and Armature. .................. + Fig. 130.—A Typical Telegraph Key, showing the Various Parts. ..... + Fig. 131.—A Typical Telegraph Sounder, showing the Various Parts. . + Fig. 132.—A Simple Home-made Telegraph Key. ....................... + Fig. 133.—A Simple Home-made Telegraph Sounder. ................... + Fig. 134.—A Diagram showing how to connect two Simple Telegraph + Stations. ......................................................... + Fig. 135.—A Complete Telegraph Set, consisting of a Keyboard and a + Sounder. .......................................................... + Fig. 136.—Details of the Telegraph Set shown in Figure 135. ....... + Fig. 137.—A Diagram showing how to connect two Complete Telegraph + Sets, using one Line Wire and a Ground. The Two-Point Switches throw + the Batteries out of Circuit when the Line is not in use. ......... + Fig. 138.—Details of the Relay Parts. ............................. + Fig. 139.—The Completed Relay. .................................... + Fig. 140.—A Diagram showing how to connect a Relay, Sounder, and + Key. Closing the Key will operate the Relay. The Relay will then + operate the Sounder in turn. ...................................... + Fig. 141.—How to hold a Telegraph Key. ............................ + Fig. 142.—The Morse Telegraphic Code. ............................. + Fig. 143.—A Microphone connected to a Telephone Receiver, and a + Battery. .......................................................... + Fig. 144.—A Very Sensitive Form of Microphone, with which the + Footsteps of a Fly can be heard. .................................. + Fig. 145.—A Telephone System, consisting of a Receiver, Transmitter, + and a Battery connected in Series. Words spoken into the Transmitter + are reproduced by the Receiver. ................................... + Fig. 146.—A Watch-Case Telephone Receiver. ........................ + Fig. 147.—A Simple Form of Telephone Receiver. .................... + Fig. 148.—A Home-made Telephone Transmitter. ...................... + Fig. 149.—A Complete Telephone Instrument. Two Instruments such as + this are necessary to form a simple Telephone System. ............. + Fig. 150.—Diagram of Connection for the Telephone Instrument shown + in Fig. 149. ...................................................... + Fig. 151.—A Desk-Stand Type of Telephone. ......................... + Fig. 152.—A Telephone Induction Coil. ............................. + Fig. 153.—Diagram of Connection for a Telephone System employing an + Induction Coil at each Station. ................................... + Fig. 154.—Details of Various Parts of a Medical Coil. ............. + Fig. 155.—Details of Interrupter for Medical Coil. ................ + Fig. 156.—Completed Medical Coil. ................................. + Fig. 157.—Diagram showing Essential Parts of Induction Coil. ...... + Fig. 158.—Empty Paper Tube, and Tube filled with Core Wire + preparatory to winding on the Primary. ............................ + Fig. 159.—Illustrating the Various Steps in winding on the Primary + and fastening the Ends of the Wire. ............................... + Fig. 160.—Complete Primary Winding and Core. ...................... + Fig. 161.—The Primary covered with Insulating Layer of Paper ready + for the Secondary. ................................................ + Fig. 162.—Simple Winding Device for winding the Secondary. ........ + Fig. 163.—Completed Secondary Winding. ............................ + Fig. 164.—Interrupter Parts. ...................................... + Fig. 165.—Condenser. .............................................. + Fig. 166.—Completed Coil. ......................................... + Fig. 167.—Diagram showing how to connect the Apparatus for the + "Electric Hands" Experiment. ...................................... + Fig. 168.—Geissler Tubes. ......................................... + Fig. 169.—The Bulb will emit a Peculiar Greenish Light. ........... + Fig. 170.—An Electrified Garbage-can. ............................. + Fig. 171.—Jacob’s Ladder. ......................................... + Fig. 172.—An X-Ray Tube. .......................................... + Fig. 173.—Fluoroscope. ............................................ + Fig. 174.—How to connect an X-Ray Tube to a Spark-Coil. ........... + An X-Ray Photograph of the hand taken with the Outfit shown in + Figure 174. The arrows point to injuries to the bone of the third + finger near the middle Joint Resulting in a Stiff Joint. .......... + Fig. 175.—Comparison between Electric Current and Flow of Water. .. + Fig. 176.—Alternating Current System for Light and Power. ......... + Fig. 177.—Motor Generator Set for changing Alternating Current to + Direct Current. ................................................... + Fig. 178.—Step-Up Transformer. .................................... + Fig. 179.—Step-Down Transformer. .................................. + Fig. 180.—Core Dimensions. ........................................ + Fig. 181.—The Core, Assembled and Taped. .......................... + Fig. 182.—Transformer Leg. ........................................ + Fig. 183.—Fiber Head. ............................................. + Fig. 184.—Leg with Heads in Position for Winding. ................. + Fig. 185.—How to make a Tap in the Primary by soldering a Copper + Strip to the Wire. ................................................ + Fig. 186.—The Transformer completely Wound and ready for Assembling. + Fig. 187.—Wooden Strips for mounting the Transformer on the Base. . + Fig. 188.—Details of the Switch Parts. ............................ + Fig. 189.—The Complete Switch. .................................... + Fig. 190.—Diagram of Connections. ................................. + Fig. 191.—Top View of the Transformer. ............................ + Fig. 192.—Side View of the Transformer. ........................... + Fig. 193.—Little Waves spread out from the Spot. .................. + Fig. 194.—A Simple Transmitter. ................................... + Fig. 195.—A Simple Receptor. ...................................... + Fig. 196.—Molded Aerial Insulator ................................. + Fig. 197.—A Porcelain Cleat will make a Good Insulator for Small + Aerials. .......................................................... + Fig. 198.—Method of Arranging the Wires and Insulating them from the + Cross Arm or Spreader. ............................................ + Fig. 199.—Various Types of Aerials. ............................... + Fig. 200.—A Ground Clamp for Pipes. ............................... + Fig. 201.—Details of the Tuning Coil. ............................. + Fig. 202.—Side and End Views of the Tuning Coil. .................. + Fig. 203.—Complete Double-Slider Tuning Coil. ..................... + Fig. 204.—A Simple Loose Coupler. ................................. + Fig. 205.—Details of the Wooden Parts. ............................ + Fig. 206.—Side View of the Loose Coupler. ......................... + Fig. 207.—Top View of the Loose Coupler. .......................... + Fig. 208.—End Views of the Loose Coupler. ......................... + Fig. 209.—Complete Loose Coupler. ................................. + Fig. 210.—A Crystal Detector. ..................................... + Fig. 211.—Details of the Crystal Detector. ........................ + A Double Slider Tuning Coil. ...................................... + A Junior Loose Coupler. ........................................... + Crystal Detectors. ................................................ + Fig. 212 Details of the "Cat Whisker" Detector. ................... + Fig. 213.—Another Form of the "Cat-Whisker" Detector. ............. + Fig. 214.—"Cat-Whisker" Detector. ................................. + Fig. 215.—Building up a Fixed Condenser. .......................... + Fig. 216.—A Fixed Condenser enclosed in a Brass Case made from a + Piece of Tubing fitted with Wooden Ends. .......................... + Fig. 217.—A Telephone Head Set. ................................... + Fig. 218.—A Circuit showing how to connect a Double-Slider Tuning + Coil. ............................................................. + Fig. 219.—Circuit showing how to connect a Loose Coupler. ......... + Fig. 220.—A Diagram showing how to connect some of the Instruments + described in this Chapter. ........................................ + Fig. 221.—A Wireless Spark Coil. .................................. + Fig. 222.—Small Spark Gaps. ....................................... + Fig. 223.—Diagram showing how to connect a Simple Transmitter. .... + Fig. 224.—A Test-Tube Leyden Jar. ................................. + Fig. 225.—Eight Test-Tube Leyden Jars mounted in a Wooden Rack. ... + Fig. 226.—A Helix and Clip. ....................................... + Fig. 227.—An Oscillation Transformer. ............................. + AN OSCILLATION HELIX. ............................................. + AN OSCILLATION CONDENSER. ......................................... + Fig 228.—Circuit showing how to connect a Helix and a Condenser. .. + Fig 229.—Circuit showing how to connect an Oscillation Transformer + and a Condenser. .................................................. + Fig 230.—An Aerial Switch. ........................................ + Fig 231.—A Complete Wiring Diagram for both the Transmitter and the + Receptor. ......................................................... + Fig. 232.—The Continental Alphabet. ............................... + Fig. 233.—A Coherer and a Decoherer. .............................. + Fig. 234.—Details of the Coherer. ................................. + Fig. 235.—The Relay. .............................................. + Fig. 236.—The Complete Coherer Outfit. ............................ + Fig. 237.—A Simple Arrangement showing the Inductive Action between + two Coils. ........................................................ + Fig. 238.—A Simple Wireless Telephone. Speech directed into the + Transmitter can be heard in the Receiver, although there is no + direct electrical connection between the two. ..................... + Fig. 239.—A Double-Contact Strap-Key. The Dotted Lines show how the + Binding-Posts are connected. ...................................... + Fig. 240.—The Circuit of the Wireless Telephone. When the Key is up, + the Receiver is ready for Action. When the Key is pressed, the + Transmitter and Battery are thrown into the Circuit. .............. + Fig. 241.—A Complete Wireless Telephone and Telegraph Station for + Amateurs. 1. The Telephone Coil. 2. The Telephone Transmitter. 3. + Double-Contact Strap-Key. 4. The Battery. 5. Spark Coil. 6. Key. 7. + Spark-Gap. 8. Aerial Switch. 9. Loose Coupler. 10. Detector, 11. + Fixed Condenser. 12. Code Chart. 13. Amateur License. 14. Aerial. + 15. Telephone Receivers. .......................................... + Fig. 242.—A Simple Electric Motor which may be made in Fifteen + Minutes. .......................................................... + Fig. 243.—Details of the Armature of the Simplex Motor. ........... + Fig. 244.—The Armature. ........................................... + Fig. 245.—The Field. .............................................. + Fig. 246.—The Field and Commutator. ............................... + Fig. 247.—The Bearings. ........................................... + Fig. 248.—The Complete Motor. ..................................... + Fig. 249.—Details of the Motor. ................................... + Fig. 250.—Complete Motor. ......................................... + Fig. 251—A Telephone Magneto. ..................................... + Fig. 252.—The Principle of the Alternator and the Direct-Current + Dynamo. ........................................................... + Fig. 253.—Details of the Armature, Commutator, and Brushes. ....... + Fig. 254.—The Complete Generator. ................................. + Fig. 255.—Details of the Field Casting. ........................... + Fig. 256.—Details of the Armature Casting. ........................ + Fig. 257.—Details of the Commutator. .............................. + Fig. 258.—Diagram showing how to connect the Armature Winding to the + Commutator. ....................................................... + Fig. 259.—Details of the Wooden Base. ............................. + Fig. 260.—The Pulley and Bearings. ................................ + Fig. 261.—The Brushes. ............................................ + THE JUNIOR DYNAMO MOUNTED ON A LONG WOODEN BASE AND BELTED TO A + GROOVED WHEEL FITTED WITH A CRANK SO THAT THE DYNAMO CAN BE RUN AT + HIGH SPEED BY HAND POWER. THE ILLUSTRATION ALSO SHOWS A SMALL + INCANDESCENT LAMP CONNECTED TO THE DYNAMO SO THAT WHEN THE CRANK IS + TURNED THE LAMP WILL LIGHT. ....................................... + Fig. 262.—Complete Dynamo. ........................................ + Fig. 263.—Complete Electric Railway operated by Dry Cells. Note how + the Wires from the Battery are connected to the Rails by means of + the Wooden Conductors illustrated in Figure 277. .................. + Fig. 264.—Details of the Floor of the Car. ........................ + Fig. 265.—Details of the Bearing which supports the Wheel and Axle. + Fig. 266.—The Wheels and Axle. .................................... + Fig. 267.—The Motor. .............................................. + Fig. 268.—The Complete Truck of the Car without the Body. ......... + Fig. 269.—Pattern for the Sides and Ends of the Car. .............. + Fig. 270.—The Roof of the Car. .................................... + Fig. 271.—The Completed Car. ...................................... + Fig. 272.–Details of a Wooden Tie. ................................ + Fig. 273.–Arrangement of Track. ................................... + Fig. 274.—Three Different Patterns for laying out the Track. ...... + Fig. 275.—Details of the Base of the Cross-over. .................. + Fig. 276.—The Completed Cross-over. ............................... + Fig. 277.—A Connector for joining the Ends of the Rails. .......... + Fig. 278.—A Bumper for preventing the Car from leaving the Rails. . + Fig. 279.—A Design for a Railway Bridge. .......................... + Fig. 280.—A Design for a Railway Station. ......................... + Fig. 281.—Miniature Carbon Battery Lamp. .......................... + Fig. 282.—Miniature Tungsten Battery Lamp. ........................ + Fig. 283.—Lamps fitted respectively with Miniature, Candelabra, and + Ediswan Bases. .................................................... + Fig. 284.—Miniature Flat-Base Porcelain Receptacle. ............... + Fig. 285.—Weather-proof and Pin-Sockets. .......................... + Fig. 286.—Types of Battery Switches suitable for Miniature Lighting. + Fig. 287.—How Lamps are Connected in Multiple. .................... + Fig. 288.—How Lamps are Connected in Series. ...................... + Fig. 289.—Three-way Wiring Diagram. The Light may be turned off or + on from either Switch. ............................................ + Fig. 290.—A Lamp Bracket for Miniature Lighting. .................. + Fig. 291.—A Home-made Bracket. .................................... + Fig. 292.—A Hanging Lamp. ......................................... + Fig. 293.—How the Reflector is made. .............................. + Fig. 294.—A Three-Cell Dry Battery for use in Hand-Lanterns, etc. . + Fig. 295.—An Electric Hand-Lantern. ............................... + Fig. 296.—An Electric Ruby Lantern. ............................... + Fig. 297.—The Electric Ruby Lamp with Glass and Shield Removed. ... + Fig. 298.—An Electric Night-Light for telling the Time during the + Night. ............................................................ + Fig. 299.—A Watch-Light. .......................................... + Fig. 300.—A "Pea" Lamp attached to a Flexible Wire and a Plug. .... + Fig. 301.—Four Steps in Carving a Skull Scarf-Pin. 1. The Bone. 2. + Hole drilled in Base. 3. Roughed out. 4. Finished. ................ + Fig. 302.—The Completed Pin ready to be connected to a Battery by + removing the Lamp from a Flashlight and screwing the Plug into its + Place. ............................................................ + Fig. 303.—How the Copper Wires (_C_) and the Silver Wires (_I_) are + twisted together in Pairs. ........................................ + Fig. 304.—Wooden Ring. ............................................ + Fig. 305.—Complete Thermopile. An Alcohol Lamp should be lighted and + placed so that the Flame heats the Inside Ends of the Wires in the + Center of the Wooden Ring. ........................................ + Fig. 306.—A Reflectoscope. ........................................ + Fig. 307.—How the Lens is Arranged and Mounted. ................... + Fig. 308.—A View of the Reflectoscope from the Rear, showing the + Door, etc. ........................................................ + Fig. 309.—A View of the Reflectoscope with the Cover removed, + showing the Arrangement of the Lamps, etc. ........................ + Fig. 310.—A Socket for holding the Lamp. .......................... + Fig. 311.—The Tin Reflector. ...................................... + Fig 312.—Top View of Lamp Bank, showing how the Circuit is arranged. + A and B are the Posts to which should be connected any Device it‘s + desirable to operate. ............................................. + Fig. 313.—A Glass Jar arranged to serve as an Electro-Plating Tank. + Fig. 314.—A Rheostat. ............................................. + Fig. 315.—A Pole-Changing Switch or Current Reverser. The Connecting + Strip is pivoted so that the Handle will operate both the Levers, A + and B. ............................................................ + COMPLETE RECEIVING SET, CONSISTING OF DOUBLE SLIDER TUNING COIL, + DETECTOR AND FIXED CONDENSER. ..................................... + COMPLETE RECEIVING SET, CONSISTING OF A LOOSE COUPLER IN PLACE OF + THE TUNING COIL, DETECTOR AND FIXED CONDENSER. .................... + Fig. 316. A Complete Wireless Receiving Outfit. ................... + Fig. 317.—Illustrating the Principle of the Tesla Coil. A Leyden Jar + discharges through the Primary Coil and a High-Frequency Spark is + produced at the Secondary. ........................................ + Fig. 318.—Details of the Wooden Rings used as the Primary Heads. .. + Fig. 319.—Details of the Cross Bars which support the Primary + Winding. .......................................................... + Fig. 320.—The Secondary Head. ..................................... + A COMPLETE COHERER OUTFIT AS DESCRIBED ON PAGE 274. ............... + THE TESLA HIGH FREQUENCY COIL. .................................... + Fig. 321.—End View of the Complete Tesla Coil. .................... + Fig. 322.—The Complete Tesla Coil. ................................ + Fig 323.—Showing how a Glass-Plate Condenser is built up of + Alternate Sheets of Tinfoil and Glass. ............................ + Fig. 324.—A Diagram showing the Proper Method of Connecting a Tesla + Coil. ............................................................. + + + + +CHAPTER I MAGNETS AND MAGNETISM + + +Over two thousand years ago, in far-away Asia Minor, a shepherd guarding +his flocks on the slope of Mount Ida suddenly found the iron-shod end of +his staff adhering to a stone. Upon looking further around about him he +found many other pieces of this peculiar hard black mineral, the smaller +bits of which tended to cling to the nails and studs in the soles of his +sandals. + +This mineral, which was an ore of iron, consisting of iron and oxygen, +was found in a district known as Magnesia, and in this way soon became +widely known as the "Magnesstone," or magnet. + +This is the story of the discovery of the magnet. It exists in legends +in various forms. As more masses of this magnetic ore were discovered in +various parts of the world, the stories of its attractive power became +greatly exaggerated, especially during the Middle Ages. In fact, +magnetic mountains which would pull the iron nails out of ships, or, +later, move the compass needle far astray, did not lose their place +among the terrors of the sea until nearly the eighteenth century. + +For many hundreds of years the magnet-stone was of little use to mankind +save as a curiosity which possessed the power of attracting small pieces +of iron and steel and other magnets like itself. Then some one, no one +knows who, discovered that if a magnet-stone were hung by a thread in a +suitable manner it would always tend to point North and South; and so +the "Magnes-stone" became also called the "lodestone," or +"leading-stone." + +These simple bits of lodestone suspended by a thread were the +forerunners of the modern compass and were of great value to the ancient +navigators, for they enabled them to steer ships in cloudy weather when +the sun was obscured and on nights when the pole-star could not be seen. + +The first real _compasses_ were called _gnomons_, and consisted of a +steel needle which had been rubbed upon a lodestone until it acquired +its magnetic properties. Then it was thrust through a reed or short +piece of wood which supported it on the surface of a vessel of water. If +the needle was left in this receptacle, naturally it would move against +the side and not point a true position. Therefore it was given a +circular movement in the water, and as soon as it came to rest, the +point on the horizon which the north end designated was carefully noted +and the ship’s course laid accordingly. + +The modern mariners’ compass is quite a different arrangement. It +consists of three parts, the _bowl_, the _card_, and the _needle_. The +bowl, which contains the card and needle, is usually a hemispherical +brass receptacle, suspended in a pair of brass rings, called _gimbals_, +in such a manner that the bowl will remain horizontal no matter how +violently the ship may pitch and roll. The card, which is circular, is +divided into 32 equal parts called the _points of the compass_. The +needles, of which there are generally from two to four, are fastened to +the bottom of the card. + +[Illustration: Fig. 1.—The Card of a Mariner’s Compass, Showing the +"Points."] + +In the center of the card is a conical socket poised on an upright pin +fixed in the bottom of the bowl, so that the card hanging on the pin +turns freely around its center. On shipboard, the compass is so placed +that a black mark, called the _lubber’s line_, is fixed in a position +parallel to the keel. The point on the compass-card which is directly +against this line indicates the direction of the ship’s head. + + +Experiments with Magnetism + + +The phenomena of magnetism and its laws form a very important branch of +the study of electricity, for they play an important part in the +construction of almost all electrical apparatus. + +Dynamos, motors, telegraphs, telephones, wireless apparatus, voltmeters, +ammeters, and so on through a practically endless list, depend upon +magnetism for their operation. + +*Artificial Magnets* are those made from steel by the application of a +lodestone or some other magnetizing force. + +The principal forms are the Bar and Horseshoe, so called from their +shape. The process of making such a magnet is called _Magnetization_. + +[Illustration: Fig. 2.—A Bar Magnet] + +Small horseshoe and bar magnets can be purchased at toy-stores. They can +be used to perform very interesting and instructive experiments. + +[Illustration: Fig. 3.—A Horseshoe Magnet] + +Stroke a large darning-needle from end to end, always in the same +direction, with one end of a bar magnet. Then dip the needle in some +iron filings and it will be found that the filings will cling to the +needle. The needle has become a magnet. + +Dip the bar magnet in some iron filings and it will be noticed that the +filings cling to the magnet in irregular tufts near the ends, with few +if any near the middle. + +[Illustration: Fig. 4.—A Magnetized Needle and a Bar Magnet which have +been dipped in Iron Filings.] + +This experiment shows that the attractive power of a magnet exists in +_two opposite_ places. These are called the poles. + +There exists between magnets and bits of iron and steel a peculiar +unseen force which can exert itself across space. + +The power with which a magnet attracts or repels another magnet or +attracts bits of iron and steel is called + +*Magnetic Force.* The force exerted by a magnet upon a bit of iron is +not the same at all distances. The force is stronger when the magnet is +near the iron and weaker when it is farther away. + +[Illustration: Fig. 5.—The Lifting Power of a Bar Magnet. _It must be +brought closer to the nails than the tacks because they are heavier_.] + +Place some small carpet-tacks on a piece of paper and hold a magnet +above them. Gradually lower the magnet until the tacks jump up to meet +it. + +Then try some nails in place of the tacks. The nails are heavier than +the tacks, and it will require a greater force to lift them. The magnet +will have to be brought much closer to the nails than to the tacks +before they are lifted, showing that the force exerted by the magnet is +strongest nearest to it. + +Magnetize a needle and lay it on a piece of cork floating in a glass +vessel of water. It will then be seen that the needle always comes to +rest lying nearly in a north and south line, with the same end always +toward the north. + +[Illustration: Fig. 6.—A Simple Compass.] + +The pole of the magnet which tends to turn towards the north is called +the _north-seeking pole_ and the opposite one is called the +_south-seeking pole_. + +The name is usually abbreviated to simply the north and south poles. The +north pole of a magnet is often indicated by a straight line or a letter +N stamped into the metal. + +A magnetized needle floating on a cork in a basin of water is a simple +form of + +[Illustration: Fig. 7.—Several Different Methods of Making a Simple +Compass.] + +*Compass.* Figure 7 shows several other different ways of making +compasses. The first method is to suspend a magnetized needle from a +fine silk fiber or thread. + +The second method illustrates a very sensitive compass made from paper. +Two magnetized needles are stuck through the sides with their north +poles both at the same end. The paper support is mounted upon a third +needle stuck through a cork. + +A compass which more nearly approaches the familiar type known as a +pocket compass may be made from a small piece of watch-spring or +clock-spring. + +The center of the needle is annealed or softened by holding it in the +flame of an alcohol lamp and then allowing it to cool. + +Lay the needle on a piece of soft metal such as copper or brass, and +dent it in the center with a punch. + +Balance the needle on the end of a pin stuck through the bottom of a +pill-box. + +*Magnetic Substances* are those which are attracted by a magnet. +Experiment with a number of different materials, such as paper, wood, +brass, iron, copper, zinc, rubber, steel, chalk, etc. It will be found +that only iron and steel are capable of being attracted by your magnet. +Ordinary magnets attract but very few substances. Iron, steel, cobalt, +and nickel are about the only ones worthy of mention. + +*Attraction through Bodies.* A magnet will attract a nail or a tack +through a piece of paper, just as if nothing intervened. + +[Illustration: Fig. 8.—The Attraction of an Iron Nail through _Glass_.] + +It will also attract through glass, wood, brass, and all other +substances. Through an iron plate, however, the attraction is reduced or +entirely checked because the iron takes up the magnetic effect itself +and prevents the force from passing through and reaching the nail. + +A number of carpet-tacks may be supported from a magnet in the form of a +chain. Each individual tack in the series becomes a _temporary_ magnet +by _induction_. + +If the tack in contact with the magnet be taken in the hand and the +magnet suddenly withdrawn, the tacks will at once lose their magnetism +and fall apart. + +[Illustration: Fig. 9.—A Magnetic Chain.] + +It will furthermore be found that a certain magnet will support a +certain number of tacks in the form of a chain, but that if a _second_ +magnet is placed beneath the chain, so that its south pole is under the +north pole of the original magnet, the chain may be lengthened by the +addition of several other tacks. + +The reason for this is that the magnetism in the tacks is increased by +induction. + +*Magnets will Attract or Repel* each other, depending upon which poles +are nearest. + +Magnetize a sewing-needle and hang it from a thread. Bring the north +pole of a bar magnet near the lower end of the needle. If the lower end +of the needle happens to be a south pole it will be attracted by the +north pole of the bar magnet. If, on the other hand, it is a north pole, +it will be repelled and you cannot touch it with the north pole of the +bar magnet unless you catch it and hold it. + +This fact gives rise to the general law of magnetism: _Like poles repel +each other and unlike poles attract each other._ + +[Illustration: Fig. 10.—An Experiment Illustrating that Like Poles Repel +Each Other and Unlike Poles Attract.] + +Another interesting way of illustrating this same law is by making a +small boat from cigar-box wood and laying a bar magnet on it. Place the +north pole of the bar magnet in the bow of the boat. + +Float the boat in a basin of water. Bring the south pole of a second +magnet near the stern of the boat and it will sail away to the opposite +side of the basin. Present the north pole of the magnet and it will sail +back again. + +[Illustration: Fig. 11.—A Magnetic Boat.] + +If the south pole of the magnet is presented to the bow of the boat the +little ship will follow the magnet all around the basin. + +The repulsion of similar poles may be also illustrated by a number of +magnetized sewing-needles fixed in small corks so that they will float +in a basin of water with their points down. + +[Illustration: Fig. 12.—Repulsion between Similar Poles, Shown by +Floating Needles.] + +The needles will then arrange themselves in different symmetrical +groups, according to their number. + +A bar magnet thrust among them will attract or repel them depending upon +its polarity. + +The upper ends of the needles should all have the same polarity, that +is, all be either north or south poles. + +Magnetism flows along certain lines called + +*Lines of Magnetic Force.* These lines always form closed paths or +circuits. The region in the neighborhood of a magnet through which these +lines are passing is called the _field of force_, and the path through +which they flow is called the + +*Magnetic Circuit.* The paths of the lines of force can be easily +demonstrated by placing a piece of paper over a bar magnet and then +sprinkling iron filings over the paper, which should be jarred slightly +in order that the filings may be drawn into the magnetic paths. + +[Illustration: Fig. 13.—A Magnetic "Phantom," Showing the Field of Force +about a Magnet.] + +The filings will arrange themselves in curved lines, diverging from one +pole of the magnet and meeting again at the opposite pole. The lines of +force are considered as extending outward from the north pole of the +magnet, curving around through the air to the south pole and completing +the circuit back through the magnet. + +[Illustration: Fig. 14.—Magnetic Phantom showing the Lines of Force +about a Horseshoe Magnet.] + +Figure 14 shows the lines of force about a horseshoe magnet. It will be +noticed that the lines cross directly between the north and south poles. + +The difference between the magnetic fields produced by like and unlike +poles is shown in Figure 15. + +[Illustration: Fig. 15.—Lines of Force between Like and Unlike Poles.] + +A study of this illustration will greatly assist the mind in conceiving +how attraction and repulsion of magnetic poles take place. + +It will be noticed the lines of force between two north poles resist +each other and meet abruptly at the center. The lines between a north +and a south pole pass in regular curves. + +*The Earth is a Great Magnet.* The direction assumed by a compass needle +is called the _magnetic meridian_. + +The action of the earth on a compass needle is exactly the same as that +of a permanent magnet. The fact that a magnetized needle places itself +in the magnetic meridian is because the earth is a great magnet with +lines of force passing in a north and south direction. + +The compass needle does not generally point exactly toward the true +North. This is because the magnetic pole of the earth toward which the +needle points is not situated at the same place as the geographical +pole. + +*Magnetic Dip.* If a sewing-needle is balanced so as to be perfectly +horizontal when suspended from a silk thread and is then magnetized, it +will be found that it has lost its balance and that the _north_ end +points slightly downward. + +[Illustration: Fig. 16.—A Simple Dipping Needle.] + +This is due to the fact that the earth is round and that the magnetic +pole which is situated in the far North is therefore not on a horizontal +line with the compass, but below such a line. + +A magnetic needle mounted so as to move freely in a vertical plane, and +provided with a scale for measuring the inclination, is called a + +*Dipping Needle.* A dipping needle may be easily made by thrusting a +knitting-needle through a cork before it has been magnetized. + +A second needle is thrust through at right angles to the first and the +arrangement carefully balanced, so that it will remain horizontal when +resting on the edge of two glasses. + +Then magnetize the first needle by stroking it with a bar magnet. When +it is again rested on the glasses it will be found that the needle no +longer balances, but dips downward. + +*Permanent Magnets* have a number of useful applications in the +construction of scientific instruments, voltmeters, ammeters, telephone +receivers, magnetos and a number of other devices. + +In order to secure a very powerful magnet for some purposes a number of +steel bars are magnetized separately, and then riveted together. A +magnet made in this way is called a compound magnet, and may have either +a bar or a horse-shoe shape. + +Magnets are usually provided with a soft piece of iron called an +armature or "keeper." The "keeper" is laid across the poles of the +magnet when the latter is not in use and preserves its magnetism. + +A blow or a fall will disturb the magnetic arrangement of the molecules +of a magnet and greatly weaken it. The most powerful magnet becomes +absolutely demagnetized at a red heat, and remains so after cooling. + +Therefore if you wish to preserve the strength of a magnetic appliance +or the efficiency of any electrical instrument provided with a magnet, +do not allow it to receive rough usage. + + + +CHAPTER II STATIC ELECTRICITY + + +If you take a glass rod and rub it with a piece of flannel or silk, it +will be found to have acquired a property which it did not formerly +possess: namely, the power of attracting to itself such light bodies as +dust or bits of thread and paper. + +Hold such a rod over some small bits of paper and watch them jump up to +meet it, just as if the glass rod were a magnet attracting small pieces +of iron instead of paper. + +The agency at work to produce this mysterious power is called +_electricity_, from the Greek word "Elektron," which means _amber_. +Amber was the first substance found to possess this property. + +[Illustration: Fig. 17.—An Electrified Glass Rod will Attract Small Bits +of Paper.] + +The use of amber begins with the dawn of civilization. Amber beads have +been found in the royal tombs at Mycenae and at various places +throughout Sardinia, dating from at least two thousand years before our +era. + +Amber was used by the ancient world as a jewel and for decoration. + +The ancient Syrian woman used distaffs made of amber for spinning. As +the spindle whirled around it often rubbed against the spinner’s +garments and thus became _electrified_, as amber always does when it is +rubbed. Then on nearing the ground it drew to itself the dust or bits of +chaff or leaves lying there, or sometimes perhaps attracted the fringe +of the clothing. + +The spinner easily saw this, because the bits of chaff which were thus +attracted would become entangled in her thread unless she were careful. +The amber spindle was, therefore, called the "harpaga" or "clutcher," +for it seemed to seize such light bodies as if it had invisible talons, +which not only grasped but held on. + +This was probably the first intelligent observation of an electrical +effect. + +In the eighteenth century, when Benjamin Franklin performed his famous +kite experiment, electricity was believed to be a sort of fiery +atmospheric discharge which could be captured in small quantities and +stored in receptacles such as Leyden jars. + +Franklin was the first to prove that the lightning discharges taking +place in the heavens are electrical. + +The story of his experiment is very interesting. + +He secured two light strips of cedar wood, placed cross-wise and covered +with a silk handkerchief for a kite. To the top of the upright stick of +the kite was fastened a sharp wire about a foot long. The twine was of +the usual kind, but was provided with a short piece of silk ribbon and a +key. The purpose of the ribbon was possible protection against the +lightning running through his body, silk being a "non-conductor," as +will be explained a little farther on. The key was secured to the +junction of the silk ribbon and the twine, to serve as a convenient +conductor from which to draw the sparks—if they came. He did not have to +wait long for a thunderstorm, and as he saw it gathering he went out +with his son, then a young man twenty-two years of age. The great clouds +rolled up from the horizon, and the gusts of wind grew fitful and +strong. The kite felt a swishing blast and began to rise steadily, +swooping this way and that as the breeze caught it. The thunder muttered +nearer and nearer and the rain began to patter on the grass as the kite +flew higher. + +The rain soon began to fall heavily, compelling Franklin and his son to +take refuge under a near-by shed. The heavy kite, wet with water, was +sailing sluggishly when suddenly a huge low-lying black cloud traveling +overhead shot forth a forked flame and the flash of thunder shook the +very earth. The kite moved upward, soaring straight into the black mass, +from which the flashes began to come rapidly. + +Franklin watched the silk ribbon and the key. There was not a sign. Had +he failed? Suddenly the loose fibers of the twine erected themselves. +The moment had come. Without a tremor he advanced his knuckle to the +key. And between his knuckle and the key passed a spark! then another +and another. They were the same kind of little sparks that he had made +hundreds of times with a _glass tube._ + +And then as the storm abated and the clouds swept off towards the +mountains and the kite flew lazily in the blue, the face of Franklin +gleamed in the glad sunshine. The great discovery was complete, his name +immortal. + +The cause of lightning is the accumulation of the electric charges in +the clouds, the electricity residing on the surface of the particles of +water in the cloud. These charges grow stronger as the particles of +water join together and become larger. As the countless multitude of +drops grows larger and larger the "potential" is increased, and the +cloud soon becomes heavily charged. + +Through the effects of a phenomenon called _induction,_ and which we +have already stumbled against in the experiment with the tacks and the +magnetic chain, the force exerted by the charge grows stronger because +of a charge of the opposite kind on a neighboring cloud or some object +on the earth beneath. These charges continually strive to burst across +the intervening air. + +As soon as the charge grows strong enough a vivid flash of lightning, +which may be from one to ten miles long, takes place. The heated air in +the path of the lightning expands with great force; but immediately +other air rushes in to fill the partial vacuum, thus producing the +terrifying sounds called _thunder_. + +In the eighteenth century, electricity was believed to be a sort of +fiery atmospheric discharge, as has been said. Later it was discovered +that it seemed to flow like water through certain mediums, and so was +thought to be a fluid. Modern scientists believe it to be simply a +vibratory motion, either between adjacent particles or in the ether +surrounding those particles. + +It was early discovered that electricity would travel through some +mediums but not through others. These were termed respectively +"conductors" and "non-conductors" or insulators. Metals such as silver, +copper, gold, and other substances like charcoal, water, etc., are good +conductors. Glass, silk, wool, oils, wax, etc., are non-conductors or +insulators, while many other substances, like wood, marble, paper, +cotton, etc., are partial conductors. + +There seems to be two kinds of electricity, one called "static" and the +other "current" electricity. The former is usually produced by friction +while the latter is generated by batteries or dynamos. + +A very simple and well-known method of generating static electricity is +by shuffling or sliding the feet over the carpet. The body will then +become _charged_, and if the knuckles are presented to some metallic +object, such as a gas-jet or radiator, a stinging little spark will jump +out to meet it. + +[Illustration: _From the author’s "Wireless Telegraphy and Telephony" by +permission._ *A Double Lightning Discharge from a Cloud to the Earth.*] + +The electricity is produced by the friction of the feet sliding over the +carpet and causes the body to become electrified. + +Warm a piece of writing-paper, then lay it on a wooden table and rub it +briskly with the hand. It soon will become stuck to the table and will +not slide along as it did at first. If one corner is raised slightly it +will tend to jump right back. If the paper is lifted off the table it +will tend to cling to the hands and the clothing. If held near the face +it will produce a tickling sensation. All these things happen because +the paper is electrified. It is drawn to the other objects because they +are _neutral_, that is, do not possess an electrical charge. + +[Illustration: Fig. 19.—A Piece of Dry Writing-Paper may be Electrified +by Rubbing.] + +All experiments with static electricity perform better in the winter +time, when it is cool and clear, than in the summer. The reason is that +the air in winter is drier than in summer. Summer air contains +considerable moisture and water vapor. Water vapor is a _partial_ +conductor of electricity, and the surrounding air will therefore conduct +the static electricity away from your apparatus almost as fast as it can +be produced in the summer time. + +[Illustration: Fig. 20.—A Surprise for the Cat.] + +Some day during the winter time, when it is cool and clear, and the cat +is near a fire or a stove, stroke the cat rapidly with the hand. The fur +will stand up towards the hand and a faint crackling noise will be +heard. The crackling is caused by small sparks passing between the cat +and the hand. If the experiment is performed in a dark room, the sparks +may be plainly seen. If you present your knuckle to the cat’s nose a +spark will jump to your knuckle and somewhat surprise the cat. + +If the day is brisk and cool, so that everything outside is frozen and +dry, try combing the hair with a rubber comb. Your hair will stand up +all over your head instead of lying down flat, and the faint crackling +noise, showing that sparking is taking place as the comb passes through +the hair, will be plainly heard. The electricity is produced by the +friction between the hair and the comb. + +Electricity may be produced by friction between a number of substances. +A hard rubber rod, a glass rod, a rubber comb or a stick of sealing-wax +may be very easily electrified by rubbing them briskly with a piece of +dry, warm flannel. + +*Electroscopes* are devices for detecting the presence of static +electricity. + +[Illustration: Fig. 21.—A Paper Electroscope.] + +A very simple form of electroscope may be made in much the same manner +as the paper compass described in the last chapter. It may be cut out of +writing-paper and mounted on a pin stuck through a cork. If an +electrified rod is held near the electroscope it may be made to whirl +around in the same manner as a compass needle when a bar magnet is +brought to it. + +*The Pith-Ball Electroscope* is a very simple device, in which a ball of +cork or elder pith is hung by a fine silk thread from an insulated +support. A suitable electroscope may be made from a glass bottle having +a piece of wire thrust into the cork to support the pith ball. When the +electrified rod is presented to the pith ball, it will fly out towards +the rod. + +[Illustration: Fig. 22.—A Pith-Ball Electroscope.] + +If the pith ball is permitted to touch the glass rod, the latter will +transfer some of its electricity and charge the ball. Almost immediately +the pith ball will fly away from the glass rod, and no matter how near +the rod is brought, it will refuse to be touched again. + +This action is much the same as that of the magnetized needle suspended +from a thread when the similar pole of the magnet is presented to it. + +When the rod is first presented to the pith ball, the latter is neutral +and does not possess an electrical charge. When the rod has touched the +ball, however, some of the electricity from the rod passes to the ball, +and after this they will repel each other. + +The reason is that the rod and the ball are _similarly_ charged and +_similarly charged bodies will repel each other_. + +[Illustration: Fig. 23.—A Double Pith-Ball Electroscope.] + +If you are a good observer you might have noticed when experimenting +with an electrified rod and the small bits of paper, that some of the +little papers were first attracted and flew upwards to the rod, but +having once touched it, were quickly repelled. + +The repulsion between two similarly electrified bodies may be shown by a +double electroscope. + +A double electroscope is made by hanging two pith balls on two silk +threads from the same support. + +Electrify a glass rod and touch it to the pith balls. They will +immediately fly apart because they are electrified with the same kind of +electricity. + +*The Gold-leaf Electroscope* is one of the most sensitive means which +can be employed to detect small amounts of static electricity. + +[Illustration: Fig. 24.—A Gold-Leaf Electroscope.] + +It is a very simple instrument and is easily made in a short time. A +couple of narrow strips of the thinnest tissue paper, or, better still, +two strips of gold leaf, are hung from a support in a wide-mouthed glass +bottle which serves at once to insulate and protect the strips from +draughts of air. + +The mouth of the jar is closed by a plug of paraffin wax, through the +center of which passes a small glass tube. A stiff copper wire passes +through the tube. The lower end of the wire is bent at right angles to +furnish support for the strips of gold leaf. A round sheet metal disk +about the size of a quarter is soldered to the upper end of the rod. + +If an electrified stick of sealing-wax or a glass rod is presented to +the disk of the electroscope, the strips will repel each other very +strongly. If the instrument is sensitive, the strips should begin to +diverge some time before the rod reaches the disk. It is possible to +make an electroscope so sensitive that chips formed by sharpening a +pencil will cause the strips to diverge. + +*There are two kinds of static electricity.* Rub a glass rod with a +piece of silk and then suspend it in a wire stirrup as shown in Figure +25. Excite a second rod also with a piece of silk and bring it near one +end of the suspended one. The suspended rod is _repelled_ and will swing +away from the one held in the hand. + +[Illustration: Fig. 25.—Method of Suspending an Electrified Rod in a +Wire Stirrup.] + +Now rub a stick of _sealing-wax_ with a piece of _flannel_ until the +sealing-wax is electrified. Then bring the stick of sealing-wax near the +end of the suspended rod. The rod will be _attracted_ to the +sealing-wax. + +If you experiment further you will find that two sticks of sealing-wax +will repel each other. + +[Illustration: Fig. 26.—Similarly Electrified Bodies Repel Each Other. +Dissimilarly Electrified Ones Attract Each Other.] + +This experiment indicates that there are two kinds of electrification: +one developed by rubbing glass with silk and the other developed by +rubbing sealing-wax with flannel. + +In the first instance, the glass rod is said to be _positively_ +electrified, and in the latter case the sealing-wax is _negatively_ +electrified. + +The same law that applies to magnetism also holds true in the case of +static electricity, and similarly electrified bodies will repel each +other and dissimilar ones attract. + +*The Electrophorus* is an instrument devised by Volta in 1775 for the +purpose of obtaining static electricity. + +[Illustration: Fig. 27.—The Electrophorous] + +It is easily constructed and will furnish a source of electricity for +quite a number of interesting experiments. An electrophorus consists of +two parts, a round cake of resinous material cast in a metal dish or +pan, and a round metal disk which is provided with an insulating handle. + +To make an electrophorus, first procure an old cake or pie tin, and fill +it with bits of resin or sealing-wax. Place the pan in a warm spot upon +the stove where the resin will melt, taking care not to overheat or it +will spatter and possibly take fire. As the resin melts, add more until +the pan is nearly full. When all is melted, remove from the fire and set +it away where it may cool and harden in the pan without being disturbed. + +Cut a circular disk out of sheet tin, zinc, or copper, making the +diameter about two inches less than that of the pie pan. Solder a small +cylinder of tin or sheet brass to the center of the disk to aid in +supporting the handle. The latter is a piece of glass tubing about +three-quarters of an inch in diameter and four or five inches long, +placed in the center of the cylinder and secured with molten +sealing-wax. + +In order to use the electrophorus the resinous cake must first be beaten +or briskly rubbed with a piece of warm woolen cloth or flannel. Then +place the disk on the cake holding the insulating handle with the right +hand. Touch the cover or the disk momentarily with the forefinger of the +left hand. After the finger is removed, raise the disk from the cake by +picking it up with the glass insulating handle. The disk will now be +found heavily charged with positive electricity, and if the knuckles are +presented to the edge, a spark will jump out to meet them. + +[Illustration: Fig. 28.—An Electric Frog-Pond.] + +The cover may then be replaced, touched, and once more removed. It will +yield any number of sparks, the resinous cake only needing to be +recharged by rubbing once in a long while. + +*An Electric Frog-Pond* may be experimented with by cutting out some +small tissue-paper frogs. Moisten them a little and lay them on the +cover of the electrophorus. Touch the electrophorus with the finger and +then raise it with the insulating handle. If the "frogs" are not too wet +they will jump from the cover upon the table as soon as the cover is +raised. + + + +CHAPTER III STATIC ELECTRIC MACHINES + + +A Cylinder Electric Machine + + +The electrophorus described in the last chapter is capable of furnishing +sufficient electricity for many interesting experiments, but for the +purpose of procuring larger supplies of electricity, a static electric +machine is necessary. + +An electric machine is composed of two parts, one for producing the +electricity by the friction of two surfaces rubbing against each other, +and the other an arrangement for collecting the electricity thus formed. + +The earliest form of electric machine consisted of a ball of sulphur +fixed upon a spindle which could be rotated by means of a crank. When +the dry hands were pressed against the sulphur by a person standing on a +cake of resin, which insulated him, sparks could be drawn from his body. + +Later a leather cushion was substituted for the hands, and a glass +cylinder for the ball of sulphur, so that the frictional electric +machine now consists of a cylinder or a disk of glass mounted upon a +horizontal axis capable of being turned by a handle. A leather cushion, +stuffed with horsehair and covered with a powdered amalgam of zinc or +tin, presses against one side of the cylinder. A "prime" conductor in +the shape of an elongated cylinder presents a row of fine metal spikes, +like the teeth of a rake, to the opposite side. A flap of silk attached +to the leather cushion passes over the cylinder and covers the upper +half. + +[Illustration: Fig. 29.—Front View of a Cylinder Electric Machine.] + +When the handle of the machine is turned, the friction produced between +the leather cushion and the glass generates a supply of positive +electricity on the glass, which is collected, as the cylinder revolves, +by the row of sharp points, and transferred to the prime conductor. + +The first thing required in the construction of an electric machine is a +large glass bottle having a capacity of from two to four quarts. + +The insulating power of glass varies considerably. Common green glass +(not white glass colored green by copper, but glass such as the +telegraph insulators are made from) generally insulates the best. Some +sorts of white glass, the Bohemian especially, are good insulators, but +this quality will not usually be found in ordinary bottles. + +[Illustration: Fig. 30.—Method of Finding the Center of a Circle.] + +Select a smooth bottle which has no lettering embossed upon it, and +stand it upon a piece of white paper. Trace on the paper a line around +the circumference of the bottle so that the circle thus formed is of the +same size as the bottom of the bottle. Lay a carpenter’s square on the +circle so that the point _C_ just touches the circumference. Draw a line +from _A_ to _B_ where the sides of the square cut the circumference. The +point in the middle of this line is the center of the circle. + +Place the paper on the bottom of the bottle so that the circle coincides +with the circumference, and mark the center of the bottle. + +The bottle must now be drilled. This is accomplished with a small +three-cornered file, the end of which has been broken off so as to form +a ragged cutting edge. The file is set in a brace and used like an +ordinary drill. During the boring process the drill must be frequently +lubricated with a mixture of gum camphor and turpentine. The drilling, +which will require almost an hour before the glass is pierced, if the +bottle is a thick one, should be performed slowly and carefully, so as +to avoid all danger of cracking the glass. The hole, when finished, +should be from one-quarter to three-eighths of an inch in diameter. + +After the hole has been bored, fit a wooden plug into the neck of the +bottle and cement it there with a mixture composed of one-half a pound +of resin, five ounces of beeswax, one-quarter of an ounce of plaster of +Paris, and three-quarters of an ounce of red ocher, melted together over +a moderately warm stove. Dip the plug in the molten cement and force it +into the neck of the bottle. When the cement dries it will be impossible +to remove it. + +The sizes of bottles vary, so that it is quite impossible to give +dimensions which must be closely followed in constructing the machine. +Those in the text are approximate. The drawings have been made to scale +so as to show the proportions the parts bear to each other. + +A heavy wooden base will be required to mount the machine on. Two +uprights are mounted on the base to support the axis of the bottle. +Through one of these bore a hole of the same diameter as the wooden plug +fitted in the neck of the bottle. The end of the wooden plug projecting +through the upright is notched and fitted with a crank so that the +bottle may be revolved. The handle of the crank is an ordinary spool +having one flange cut off and mounted with a screw and a washer. + +[Illustration: Fig. 31.—The "Rubber."] + +The machine is now ready for the "rubber" and "prime conductor." The +rubber is a piece of wood one inch square and from six to eight inches +long. A piece of undressed leather is tacked on as shown in the +illustration and stuffed with horsehair. The wood is shellacked and +covered with tin-foil previous to tacking on the leather. A strip of +wood, two inches wide and one-half an inch thick, is fastened to the +back of the rubber. The strip should be just long enough so that when +the lower end rests on the base the rubber is level with the axis of the +bottle. The lower end may be fastened to the base by means of a small +brass hinge. Two rubber bands stretch from hooks between the rubber and +the base so as to pull the former tightly against the bottle. The +illustration shows a method of mounting the rubber on a foot-piece held +to the base with a thumb-nut so that it may be slid back and forth and +the pressure varied at will. + +The prime conductor is formed from a piece of curtain-pole two inches in +diameter and eight inches long. The ends are rounded with a rasp and +then smoothed with sandpaper. The whole surface is then shellacked and +covered with a layer of tinfoil. The heads of a number of dressmaker’s +pins are cut off, and the pins forced into the side of the prime +conductor with a pair of pincers. They should form a row like the teeth +of a rake about three-eighths of an inch apart. A hole is bored in the +center of the under side of the prime conductor to receive a glass rod +one-half inch in diameter. A second hole of the same size is bored in +the base in such a position that when the glass rod is in place, the +teeth on the prime conductor are on a level with the axis of the bottle, +and their points about 3-32 of an inch away from the glass. The glass +rod must be used in order to insulate the prime conductor and prevent +the escape of the electricity. It is secured with some of the cement +described on page 33. A piece of water-gauge glass may be used in place +of a glass rod. + +[Illustration: Fig. 32.—The Prime Conductor or Collector.] + +A strip of oiled silk, or in its place a strip of silk which has been +shellacked, eight or nine inches wide, and long enough to reach half-way +around the bottle, is tacked to the rubber so that the silk covers the +upper half of the cylinder and comes over to within one-quarter of an +inch of the steel points. + +The machine is now complete, and when the handle is turned rapidly, you +will be able to draw sparks from the prime conductor. The sparks will +probably be very short, about one-half of an inch long. These can be +increased, however, to three inches, if the glass is of the right +quality, by treating the rubber with amalgam. + +The amalgam is formed by melting one ounce of tin and adding to it one +ounce of zinc in small bits. As soon as the zinc has also melted add to +the mixture two ounces of mercury which has been previously warmed. Be +careful not to inhale any of the vapor during this operation. Pour the +mixture into a vessel of cold water, which will reduce the metal to +small grains. Pour off the water and grind the amalgam to a powder by +pounding the grains with a hammer. + +The leather rubber should be _thinly_ smeared with lard and the powdered +amalgam rubbed on it. + +In order to obtain the greatest effect from an electric machine, it must +be carefully freed from dust and particles of amalgam adhering to the +glass, and the insulating column rubbed with a warm woolen cloth. The +best results are obtained by placing the machine near a stove or +radiator where it is warm. + +[Illustration: Fig. 33.—The Complete Cylinder Electric Machine.] + + +A Wimshurst Machine + + +The Wimshurst Machine consists of two varnished glass plates revolving +in opposite directions. On the outside of each of these plates are +cemented a number of tinfoil "sectors," arranged radially. Two +conductors at right angles to each other extend obliquely across the +plates, one at the back and the other at the front. These conductors +each terminate in brushes of tinsel which electrically excite the +"sectors" as the plates revolve. The electricity is collected by a set +of "collectors" arranged in a somewhat similar manner to the collector +on the cylinder electric machine. + +*The Glass Plates* are each eighteen inches in diameter. Purchase two +panes of clear glass twenty inches square from a glass dealer. The white +glass is far preferable to the green glass and will make the best +electric machine. The plates should be of the thickness known as "single +light" and should be perfectly free from wavy places, bubbles, or other +imperfections. + +[Illustration: Fig. 34.—Paper Pattern for laying out the Plates.] + +The work is first laid out on a piece of stiff paper twenty inches +square as a pattern. Describe a circle four inches in diameter. Using +the same center, draw other circles, making them respectively eight, +sixteen, and eighteen inches in diameter. Then mark sixteen radial +lines, from the center, making them equal distances apart, as shown in +Figure 34. + +[Illustration: Fig. 35.—Plate with Sectors in Position, and a Pattern +for the Sectors.] + +Lay one of the glass panes over the pattern and cut out a glass circle +eighteen inches in diameter, or perhaps you may be able to have a +glazier do the cutting for you and so save considerable trouble and +possible breakage. Two such plates should be made. + +The Sectors are cut from heavy flat tinfoil according to the pattern +shown in Figure 35. They should be made one inch and one-half wide at +the wide end and three-quarters of an inch at the other end. They are +each four inches long. Thirty-two such sectors are required. The easiest +way to make them is to cut out a pattern from heavy cardboard to serve +as a guide. + +Clean and dry both of the glass plates very carefully and then give them +each two thin coats of white shellac. After they have been dried, lay +one of the plates on the paper pattern so that the outside of the plate +will coincide with the largest circle on the paper. + +Then place a weight in the center of the plate so that it will not move, +and stick sixteen of the tinfoil sectors on the plate with thick +shellac. The sectors are arranged symmetrically on the plate, using the +eight-inch and sixteen-inch circles and the radial lines as guides. Both +plates should be treated in this manner. Each sector should be carefully +pressed down on the glass, so that it will stick smoothly without +air-bubbles or creases. When all the sectors are in place the plates +will appear like that shown in Figure 35. + +*The Bosses* will have to be turned out at a wood-working mill or at +some place where they have a turning-lathe. The bosses are four inches +in diameter at the large end and one inch and one-half at the other. A +groove is turned near the small end of each to accommodate a round +leather belt. + +A hole should be made in each boss about half-way through from the small +end. These holes should be bushed with a piece of brass tubing having an +inside diameter of one-half inch. The tubing should go into the hole +very snugly and be a "driven fit." + +[Illustration: Fig. 36.—A Side View of one of the Bosses, showing the +Brass Bushing used.] + +The bosses should both be given a coat of shellac, and after this is +dry, fastened to the glass plates on the same side to which the tinfoil +sectors are attached. The best plan is to lay the disks on the paper +pattern and adjust them until the outer edge coincides with the largest +circle. + +Then apply some _bichromate glue_ to the flat surface of one of the +bosses and place the latter in the center of the plate in line with the +smallest circle. + +Place a weight on the boss to hold it down firmly against the plate and +leave it over night, or for ten or twelve hours, until thoroughly dry. + +The glue is prepared by placing some high-grade glue in a tin cup and +covering it with cold water. Allow it to stand until the glue absorbs +all the water it will and becomes soft. Then pour the water off and add +enough _glacial acetic acid_ to cover the glue. + +Heat the mixture until it is reduced to a liquid, stirring it until it +is perfectly smooth. Add a teaspoonful of powdered bichromate of potash +to the glue. + +The glue must now be kept in the dark, for sunlight will "set" the glue +so that it becomes insoluble. + +The Frame of the machine is composed of two strips twenty-five inches +long, three inches wide, and an inch and one-half in thickness, and two +cross-pieces of the same thickness and width fifteen inches long. + +[Illustration: Fig. 37.—The Frame.] + +Notches are cut at both sides of the base to admit the feet of the +uprights. + +*The Uprights* are seventeen inches long, three inches wide, and one and +one-half inches thick. + +[Illustration: Fig. 38.—The Upright.] + +The notch at the foot is cut the same width as the thickness of the long +members of the frame and is arranged so that when fitted in place, the +foot of the upright will rest on the table in line with the bottom of +the cross-pieces. + +*The Driving-Wheels* are turned out of wood on a lathe. They are seven +inches in diameter and seven-eighths of an inch thick. A groove should +be turned in the edge to carry a small round leather belt. The wheels +are mounted on a wooden axle made from a round curtain-pole. They are +glued to the axle and arranged so that the grooves will fall directly +underneath the pulleys turned in the bosses. + +[Illustration: Fig. 39.—The Driving-Wheels and Axle.] + +The ends of the axle pass through the uprights, five inches above the +bottom. + +The front end of the axle is fitted with a crank and a handle. + +[Illustration: Fig. 40—The Boss and Axle. For sake of clearness, the +Plate is not shown.] + +The plates are mounted on short iron axles passing through the top of +the upright into the brass bushings. One end of each of the axles is +filed flat where it passes through the wood upright so that it may be +firmly held by a set-screw and prevented from revolving. + +Fasten a small fiber washer to the center of one glass disk so that it +will separate the plates and prevent them from touching when revolving. + +The collectors, quadrant rods, etc., are mounted on glass rods one inch +in diameter. The bottoms of the rods fit in holes (_H H_) bored in the +cross-pieces of the base, Figure 37. The upper ends are each fitted with +a brass ball two inches in diameter. The balls are mounted on the rods +by soldering a piece of brass tubing to the ball and slipping it over +the rod. The rods should be of the proper length to bring the center of +the balls on a line with the center of the plates. + +[Illustration: Fig. 41—Showing how the Ball, Comb, etc., are mounted on +the Glass Rod.] + +Make two forks as shown in Figure 42 out of brass rod, three-sixteenths +of an inch in diameter and solder brass balls at the ends. The forks are +eleven inches long. + +A number of small holes must be bored in the "prongs" and pins made by +cutting ordinary dressmakers’ pins in half and soldering them in place. +These pins, mounted on the forks, form the combs or collectors. + +Bore a horizontal hole through each of the brass rods on the top of the +glass rods and pass the shanks of the forks through and solder them in +place. + +One of the shanks may be provided with a discharge ball at the end as +shown by _D B_ in Figure 44. The other is provided with a hard rubber +handle made from a piece of rod. Bore a three-eighths hole directly in +the top of each brass ball to receive the quadrant rods forming the +spark-gap. + +[Illustration: Fig. 42.—A Comb or Collector.] + +The quadrant rods extend over the top of the plates and are +three-eighths of an inch in diameter. They are loose in the tops of the +balls so that they may be moved about or removed entirely. + +A small brass ball three-quarters of an inch in diameter should be +soldered to the top of one of the quadrant rods and a similar ball two +inches in diameter to the other. + +[Illustration: Fig. 43.—Showing how the Tinsel Brushes are arranged on +the "Neutralizer" Rods.] + +Two large brass balls, two inches in diameter, are fitted over the ends +of the axles, which project through the uprights. Bore a +one-quarter-inch hole through each ball at right angles to the axle and +slip a one-quarter-inch brass rod through and solder it fast. + +[Illustration: Fig. 44.—The Complete Wimshurst Electric Machine. B B B +B, _Brushes_. C C, _Combs_. D B, _Discharge Ball_. I I, _Glass Rods_. H, +_Handle_. Q Q, _Quadrant Rods_. S S S S S, _Sectors_. S G, _Spark-Gap_. +P P, _Driving-Wheels_. For the sake of clearness, several of the sectors +are not shown.] + +The ends of the rods should be tipped with a bunch of tinsel or fine +copper wires and be curved so that the brushes so formed will just touch +the sectors on the disks when the latter are revolved. + +These are the neutralizers and are arranged in the approximate positions +shown in Figure 44. + +The driving-wheels are connected to the bosses by means of small round +leather belts. The belt at the rear of the machine is crossed in order +to make the plates revolve in opposite directions. + +If the machine has been properly built it is now ready for operation. It +may be necessary to charge the machine the first time that it is used by +touching several of the sectors with the charged cover of an +electrophorus. Then if the handle is turned the accumulated electricity +should discharge across the spark-gap at the top of the machine in the +form of bright blue sparks. + + +Experiments with an Electric Machine + + +Many interesting experiments can be performed with an electric machine. +The number is almost unlimited. A few of the most instructive ones are +described below. Others can be found in almost any text book on physics. + +*The Leyden jar* consists of a glass jar coated with tinfoil part way up +on both the outside and inside. Through the wooden stopper passes a +brass rod or a heavy copper wire which connects with the inner coating +of tinfoil by means of a small brass chain. The upper and outside end of +the rod usually terminates in a brass ball or knob. + +It is a very simple matter to make a good Leyden jar. + +[Illustration: Fig. 45.—The Leyden Jar.] + +The jar must be thoroughly cleaned and dried before coating. The inside +is then given a thorough brushing over with shellac or varnish. Before +it is dry, carefully insert the tin-foil and press it smoothly against +the glass. The outside of the jar is treated and coated in the same +manner. The inside and outside of the bottom are also coated by cutting +the tinfoil in circular pieces and shellacking them on. + +In order to charge the Leyden jar, grasp it in the hand near the bottom +and hold the knob against the prime conductor while turning the handle +of the machine. + +[Illustration: Fig. 46.—A Wooden Mortar for Igniting Gunpowder.] + +*Igniting gunpowder.* Bore a hole one-half inch in diameter and one inch +deep in a block of hardwood. Pass two small brass wires through holes in +the sides, letting the ends of the wires be about one-eighth of an inch +apart. Pour a little gunpowder in loosely over the wires. Tie a piece of +thoroughly moistened cotton twine, three inches long, to one of the +wires and attach it to the outside coating of a charged Leyden jar. + +Connect the knob of the jar to the other wire. The gunpowder will +immediately explode. Keep the face and hands away from the gunpowder +when performing this experiment. + +[Illustration: Fig. 47.—An Electric Umbrella.] + +*Electric Umbrella.* The repulsion of similarly electrified bodies which +was illustrated by the action of the pith ball electroscope may be +better illustrated by pasting some narrow streamers of tissue paper +about one-eighth of an inch wide and four inches long to a small cork +covered with tinfoil. The cork is mounted on the upper end of a stiff +copper wire supported in a bottle. When the wire is connected to the +prime conductor and the machine set in motion, the strips will spread +out like an umbrella. + +*Lightning Board.* A pane of glass is thoroughly cleaned and then given +a coat of shellac or varnish. Before the varnish is dry, press on a +piece of tinfoil large enough to cover one side of the glass and rub it +down smoothly. + +[Illustration: Fig. 48.—A Lightning Board.] + +After the shellac or varnish is dry, cut the tinfoil up into innumerable +little squares with a sharp knife and ruler, leaving two solid strips of +tinfoil at the ends of the glass pane. + +The pane is mounted by cementing it in a slot in the cork of a bottle. +Connect one of the tinfoil strips to the prime conductor and the other +to the earth or the body. When the machine is turned, innumerable little +sparks will pass between the tinfoil squares and give an appearance very +similar to that of lightning. + +[Illustration: Fig. 49.—An Electric Dance.] + +*The Electrical Dance.* A number of little balls of cork or pith are +enclosed in a cylinder of glass about two and one-half or three inches +high formed by cutting off the top of a lamp chimney. The top and bottom +of the cylinder are closed by two circular pieces of sheet brass or +copper. The top disk is connected to the prime conductor while the +bottom one is connected to the rubber. When the machine is set in +motion, the little balls will dance up and down. Bits of feather or +paper cut to represent figures of men and women may be used as well as +pith or cork balls. + +*The Electric Whirl.* The whirl consists of an S shaped piece of brass +wire, pointed at both ends and supported on a needle by a little conical +depression made in the center with a punch. + +[Illustration: Fig. 50.—An Electric Whirl.] + +The needle is stuck in a cork in the top of a bottle and connected with +the prime conductor of the electric machine. When the latter is set in +motion, the whirl will commence to revolve at a high rate of speed. + +*Lichtenberg’s Figures* can be produced by charging a Leyden jar by +connecting the knob or inside coating with the prime conductor and +holding the outside coating in the hand. + +Then trace a small circle on the electrophorus bed with the knob. + +Charge a second Leyden jar by connecting the outside coating with the +prime conductor. + +The inside coating should be connected to the rubber by means of a wire +fastened to the knob. The same result may be obtained by connecting the +outside coating with the prime conductor and touching the knob with the +hand. + +Then trace a cross on the electrophorus bed with the knob, making the +cross inside of the circle. + +[Illustration: Fig. 51.—Lichtenberg’s Figures.] + +Shake a mixture of red lead and sulphur through a muslin bag from a +height of several inches over the electrophorus. + +The red lead will accumulate around the cross and the sulphur around the +circle. + + + +CHAPTER IV CELLS AND BATTERIES + + +In order that the young experimenter may obtain electricity for driving +his various electrical devices it is necessary to resort to batteries, a +small dynamo, or the house-lighting current. + +All houses are not supplied with electric current. Furthermore, many +boys have no source of power from which to drive a small dynamo. +Batteries must therefore be resorted to in the majority of cases. + +A number of different cells and batteries are described in this chapter. +All of them are practical, but after buying zinc, chemicals, etc., for +any length of time, figure out what your batteries _cost_ you to make. +The real value is not their cost in dollars and cents but in what you +have _learned_ in making them. If you have a continuous use for +electrical current for running _small_ electrical devices it is cheaper +to buy dry cells, or what is better, a _storage battery_, and have it +_recharged_ when necessary. + +_Build your own batteries first_. Then after you have learned how they +are made and something about their proper care buy them from some +reliable electrical house. + +Batteries are always interesting to the average experimenter, and when +properly made are one of the most useful pieces of apparatus around the +home, laboratory, or shop that it is possible to construct. Many +hundreds of thousands of experiments have been carried out by capable +men in an effort to discover or devise a perfect battery, and the list +of such cells is very great. + +Only the most common forms, which are simple and inexpensive to +construct but will at the same time render fair service, have been +chosen for description. + +Cells are usually considered _one_ element or jar of a battery. A _cell_ +means only one, while a _battery_ is a _group_ of cells. It is not a +proper use of the word to say "battery" when only _one_ cell is implied. +This is a very common error. + +*The Voltaic cell* is called after its inventor, Volta, a professor in +the University of Pavia, and dates back to about the year 1786. + +[Illustration: Fig. 52.—The Voltaic Cell.] + +A simple voltaic cell is easily made by placing some water mixed with a +little sulphuric acid in a glass tumbler and immersing therein two clean +strips, one of zinc and the other of copper. The strips must be kept +separate from each other. The sulphuric acid must be diluted by mixing +it with about ten times its volume of water. In mixing acid with water +always remember never to pour water into acid but to perform the +operation the other way and pour the acid into the water. A copper wire +is fastened with a screw or by soldering to the top of each of the +strips, and care must be exercised to keep the wires apart. + +As has been said, the zinc and copper must never be allowed to touch +each other in the solution, but must be kept at opposite sides of the +jar. + +The sulphuric acid solution attacks the zinc, causing it slowly to waste +away and disappear. This action is called _oxidation_, and in reality is +a very slow process of burning. The consumption of the zinc furnishes +the electric energy, which in the case of this cell will be found to be +sufficient to ring a bell or buzzer, or run a very small toy motor. + +As soon as the plates are immersed in the acid solution, bubbles will +begin to rise from the zinc. These bubbles contain a gas called hydrogen +and they indicate that a chemical action is taking place. The zinc is +being dissolved and the _hydrogen_ gas is being set free from the acid. +It will be noticed that no bubbles arise from the copper plate and that +there is little if any chemical action there. In other words, it seems +that the chemical action at one plate is stronger than that at the +other. + +A cell might be likened to a furnace in which the zinc is the fuel which +is burned to furnish the energy. We know that if the zinc is burned or +oxidized in the open air it will give out energy in the form of _heat_. +When it is burned or oxidized slowly in acid in the presence of another +metal it gives out its energy in the form of _electricity_. The acid +might be likened to the fire, and the copper to a hand which dips into +the cell to pick up the current and takes no part chemically. + +If a wire is connected to each of the plates and the free ends of the +wires touched to the tip of the tongue it will produce a peculiar salty +taste in the mouth indicating the presence of a current of electricity. + +If the wires are connected to an electric bell, the bell will ring, or, +instead, the current may be used to run a small motor. If the cell is +made of two zinc plates or two copper plates, the bell will not ring, +because no electricity will be produced. In order to produce a current, +the electrodes must be made of two different materials upon which the +acid acts differently. Current may be obtained from a cell made with a +zinc and carbon plate or from one with zinc and iron. + +Therefore, in order to make a battery it is necessary to have a metal +which may be consumed, a chemical to consume or oxidize it, and an +inactive element which is merely present to collect the electricity. + +When the wires connected to the two plates are joined together, a +current of electricity will flow from the copper plate through the wire +to the zinc. The copper is known as the _positive_ pole and the zinc as +the _negative_. + +A simple voltaic cell may be easily made by cutting out a strip of zinc +and a strip of copper, each 3 1/2 inches long, and one inch wide. A +small hole bored through the upper end of the strips will permit them to +be mounted on a wooden strip with a screw as shown in Figure 53. The +connecting wires are placed under the heads of the screws. Care should +be exercised to arrange the screws used for mounting the electrodes to +the wooden strip so that they do not come exactly opposite, and there is +no danger of the points touching and forming a short circuit. + +[Illustration: Fig. 53.—The Elements of Simple Voltaic Cell.] + +[Illustration: Fig. 54.—A Home-Made Voltaic Cell.] + +An ordinary tumbler or jelly glass will make a good battery jar. The +exciting liquid should be composed of + +One part of sulphuric acid +Ten parts of water + +One of the disadvantages of the voltaic cell is that it becomes +_polarized_, that is, small bubbles of hydrogen which are liberated by +the chemical action collect on the copper plate and cause the strength +of the battery to fall off rapidly. + +There are a great number of _elements_, as the zinc and copper are +called, and an even greater number of different solutions or _excitants_ +which can be employed in place of sulphuric acid to make a cell, forming +an almost endless number of possible combinations. + +*Leclanche Cell.* One of the most common forms of cell employed for +bell-ringing, telephones, etc., is called the Leclanche cell, after its +inventor, and consists of two elements, one of zinc and the other of +carbon, immersed in a solution of _sal ammoniac_ or _ammonium chloride_. +This cell has an E. M. F. of 1.4 volts, which is about half as much +again as the voltaic cell. + +[Illustration: Fig. 55.—Carbon-Cylinder Cell, and Cylinder.] + +The most common form of Leclanche cell is illustrated in Figure 55. This +type is usually known as a "carbon cylinder" cell because the positive +element is a hollow carbon cylinder. The zinc is in the form of a rod +passing through a porcelain bushing set in the center of the carbon +cylinder. A battery of such cells can only be used successfully for open +circuit work. The "open circuit" is used for bells, burglar alarms, +telephone circuits, etc., or wherever the circuit is such that it is +"open" most of the time and current is only drawn occasionally and then +only for short periods. + +If the current is drawn for any appreciable length of time hydrogen gas +will collect on the carbon cylinder and the cell will become +_polarized_. When polarized it will not deliver much current. + +Many methods have been devised for overcoming this difficulty, but even +the best of them are only partially successful. + +The usual method is to employ a chemical _depolarizing_ agent. Figure 56 +shows a Leclanche cell provided with a _depolarizer_. + +The carbon is in the form of a plate placed in a _porous cup_ made of +earthenware and filled with _manganese dioxide_. + +Chemists class _manganese dioxide_ as an _oxidizing_ agent, which means +that it will furnish oxygen with comparative ease. Oxygen and hydrogen +have a strong _chemical affinity_ or attraction for each other. + +[Illustration: Fig. 56.—A Leclanche Cell, showing the Porous Cup.] + +If the carbon plate is packed in manganese dioxide any hydrogen which +tends to collect on the carbon and polarize the cell is immediately +_seized_ by the oxygen of the manganese dioxide and united with it to +form water. + +This form of Leclanche cell is called the disk type. It is capable of +delivering a stronger current for a longer period of time than the +carbon cylinder battery. The zinc is usually made in the form of a +cylinder, and fits around the outside of the porous cup. + +*Dry Cells* are used extensively nowadays for all open circuit work on +account of their convenience and high efficiency. + +The dry cell is not, as its name implies, "dry," but the exciting agent +or electrolyte, instead of being a liquid, is a wet paste which cannot +spill or run over. The top of the cell is poured full of molten pitch, +thus effectively sealing it and making it possible to place the cell in +any position. + +Dry cells can be purchased from almost any electrical house or garage +for twenty-five cents each. It will therefore hardly pay the young +experimenter to make his own _dry cells_. For the sake of those who may +care to do so, however, directions for building a simple but efficient +dry cell of the type used for door-bells and ignition work, will be +found below. + +[Illustration: Fig. 57.—A Dry Cell.] + +The principle of a dry cell is the same as that of a Leclanche cell of +the disk type. The exciting solution is _ammonium chloride_, the +electrodes or elements are zinc and carbon, and the carbon is surrounded +by manganese dioxide as a depolarizing agent. + +Obtain some sheet zinc from a plumbing shop or a hardware store and cut +out as many rectangles, 8 x 6 inches, as it is desired to make cells. +Also cut out an equal number of circles 2 3/8 inches in diameter. + +Roll the sheets up into cylinders 2 3/8 inches in diameter inside and 6 +inches long. The edges are lapped and soldered. Fit one of the round +circles in one end of each of the cylinders and solder them securely +into place, taking care to close up all seams or joints which might +permit the electrolyte to escape or evaporate. + +Secure some old carbon rods or plates by breaking open some old dry +cells. The carbons will be in the form of a flat plate, a round rod, or +a star-shaped corrugated rod, depending upon the manufacture of the +cell. Any of these types of carbons will serve the purpose well, +provided that they are fitted with a thumb-screw or a small bolt and nut +at the top so as to make wire connections with the carbon. + +Make a wooden plunger of the same shape as the carbon which you may +select, but make it slightly larger. Smooth it with sandpaper and give +it a coat of shellac to prevent it from absorbing moisture. + +This wooden plunger is temporarily inserted in the center of one of the +zinc cups and supported so that it will be about one-half inch above the +bottom. + +The electrolyte is prepared by mixing together the following ingredients +in the proportions shown: + +Sal Ammoniac. 1 part +Zinc Chloride. 1 part +Plaster of Paris. 3 parts +Flour. 3/4 part +Water. 2 parts + +[Illustration: Fig. 58.—The Different Operations involved in Making a +Dry Cell.] + +The above paste is then firmly packed into the zinc shell around the +wooden plunger, leaving a space of about 3/4 of an inch at the top. The +paste can be poured in very readily when first mixed but sets and +hardens after standing a short while. + +After it has set, withdraw the wooden plunger, thus leaving a space +inside of the dry cell a little larger than the carbon. The carbon is +now inserted in this hole and the surrounding space is filled with a +mixture composed of: + +Sal Ammoniac. 1 part +Zinc Chloride. 1 part +Manganese Dioxide. 1 part +Granulated Carbon. 1 part +Flour. 1 part +Plaster of Paris. 3 parts +Water. 2 parts + +The granular carbon may be had by crushing up some old battery carbons. +The parts given in both of the above formulas are proportioned so that +they may be measured by bulk and not by weight. An old teaspoon or a +small cup will make a good measure. + +Each one of the zinc shells should be filled in this manner. After they +have all been filled, clean off the top edge of the zinc and pour the +remaining space in the cell full of molten tar or pitch so as to seal it +over. + +Solder a small binding-post to the top edge of the zinc to facilitate +connection. Then wrap the cells in several thicknesses of heavy paper to +prevent them from short circuiting, and they are ready for use. + +A small hole bored through the sealing material after it is dry will +provide a vent for the escape of gases. + +*Recharging dry cells* is a subject that interests most experimenters. + +Dry cells very often become useless before the zinc shell is used up or +the chemicals are exhausted, due to the fact that the water inside of +the cell dries up and the resistance therefore becomes so great that it +is practically impossible for the current to pass. + +The life of such cells may be partially renewed by drilling several +holes in the cell and permitting it to soak in a strong solution of sal +ammoniac until some of the liquid is absorbed. The holes should then be +plugged up with some sealing wax in order to prevent evaporation. + +An old dry cell may be easily turned into a "wet" cell by drilling the +zinc full of holes and then setting it in a jar containing a sal +ammoniac solution. The battery should be allowed to remain in the +solution. + +*Wet batteries* are very much easier to make than dry batteries and are +capable of delivering more current. + +They have the disadvantage, however, of wasting away more rapidly, when +not in service, than dry cells. + +The Leclanche cell is the type generally first attempted by most +experimenters. + +*Carbon plates* for making such a battery are most easily and cheaply +obtained from old dry cells. About the only way that a dry cell can be +broken open is with a cold-chisel and a hammer. Care must be taken, +however, in order not to break the carbon. + +Ordinary jelly-glasses make good jars for small cells. Fruit-jars may be +used for larger batteries by cutting the tops off so that the opening is +larger. The carbon plate contained in a dry cell is usually too long for +a jar of this sort and must be broken off before it can be used. The +lower end is the one which should be broken because the top carries a +binding-post, with which connections can be made. A small hole is bored +in the carbon rod at a distance from the bottom equal to the height of +the jar which is to be used. + +[Illustration: Fig. 59.—A Zinc-Carbon Element, made from Heavy plates.] + +Considerable care must be used in boring carbon because it is very +brittle and easily cracks. Only very light pressure should be used on +the drill. The carbon is fastened to a strip of wood, about an inch and +one-quarter wide, one-half an inch thick, and a little longer than the +top of the glass jar is wide. + +[Illustration: Fig. 60.—A Method of making a Cell Element from Carbon +Rods.] + +A piece of heavy sheet zinc is fastened on the other side opposite the +carbon, with a screw. It is a good idea to paint the screws and the +surrounding portions of both the zinc and the carbon with hot paraffin +wax so that the solution will not "creep" and attack the screws. It is +also a good plan first to soak the wooden strip in some hot paraffin +until it is thoroughly impregnated. + +Ammonium chloride, or, as it is more commonly called, sal ammoniac, +should be added to a jar of water until it will dissolve no more. The +zinc and carbon elements may then be placed in the solution. + +One of the great disadvantages of the voltaic cell is that the zinc is +attacked by the acid when the battery is not in use and cannot be +allowed to remain in the solution without quickly wasting away. This is +true in the case of the Leclanche cell only to a very small extent. The +voltaic cell is more powerful than the Leclanche cell, but the elements +must be carefully lifted out and rinsed with water every time that you +are through using the cell. By using several carbon plates instead of +one, the cell may be made more powerful. The illustrations show several +ways of accomplishing this. The simplest method is to place a carbon +plate on each side of the wooden strip and use a zinc in the form of a +rod which passes through a hole between the two. Care must always be +used to keep any screws which are used to hold the carbons or zincs in +position in the cells from touching each other. + +[Illustration: Fig. 61. An Element made from two Carbon Plates and a +Zinc Rod.] + +In Figure 62 an arrangement of using four carbons is shown. The drawing +is self-explanatory. In any of the cells using more than one carbon +element, the carbons should all be connected. + +In discussing the voltaic cell we mentioned the fact that it becomes +polarized, and explained this phenomenon as being caused by hydrogen +bubbles collecting on the copper or positive pole. The same thing +happens in the case of carbon or any other material which is used as a +positive. + +*Polarization* is the "bugbear" of batteries. It can be eliminated to a +certain extent, however, by the use of a "depolarizer" _placed in the +solution_. There are several such substances, the most common being +_sodium bichromate_ and _potassium bichromate_. These are used in +battery preparations on the market called "Electric Sand," "Electropoian +Fluid," etc. + +[Illustration: Fig. 62. A Method of Mounting four Carbon Plates.] + +When one of these is added to a sulphuric acid solution, using zinc and +carbon as the battery elements, it forms a very powerful cell, having E. +M. F. of two volts. + +A battery solution of this kind may be prepared by adding four ounces of +bichromate of potash to a solution composed of four ounces of sulphuric +acid mixed with sixteen ounces of water. The battery will give a more +powerful current for a longer time when this solution is used instead of +the plain sulphuric acid and water or sal ammoniac. + +[Illustration: Fig. 63.—A Battery Element arranged for three Cells.] + +It might be well at this time to caution the experimenter against the +careless handling of sulphuric acid. It is not dangerous if handled +properly, but if spilled or spattered around carelessly it is capable of +doing considerable damage to most things with which it comes in contact. +Do not attempt to use it in any place but a shop or cellar. The smallest +drop coming in contact with any organic matter such as woodwork, +clothing, carpets, etc., will not only discolor any of the latter, but +eat a hole in it. The best thing to use to counteract the effects of the +acid which has been spilled or spattered is water in sufficient quantity +to drench things and dilute the acid enough to render it harmless. A +little strong ammonia will neutralize the acid and sometimes restore the +color to clothing which has been burned by acid. + +[Illustration: Fig. 64.—A Plunge Battery, with Windlass.] + +All acid batteries of this sort have the one objection that it is +impossible to leave the elements in the solution without wasting the +zinc. The usual way to arrange the battery cells so that the elements +may be removed from the solution most easily is to fasten the elements +to a chain or cord passing over a windlass fitted with a crank so that +when the crank is turned the elements may be raised or lowered as +desired. + +A "plunge battery" of this sort is illustrated in Figure 64. The +construction is so plainly shown by the drawing that it is hardly +necessary to enter into the details. The crank is arranged with a +dowel-pin which passes through into a hole in the frame, so that when +the elements are lifted out of the solution the pin may be inserted in +the hole and the windlass prevented from unwinding. + +[Illustration: Fig. 65.—A Plunge Battery adapted to a Set of Elements, +as shown in Figure 63. They may be lifted out and placed on the "Arms" +to drain.] + +A somewhat easier method of accomplishing the same result is that shown +by Figure 65. In this, the elements are simply raised up out of the jars +and laid across the two "arms" to drain. + +*The Edison-Lalande* cell employs a block of pressed copper oxide as the +positive element, while two zinc plates form the negative. The exciting +liquid is a strong solution of caustic soda. + +[Illustration: Fig. 66.—An Edison-Lalande Cell.] + +The copper oxide acts both as the positive element and as a depolarizer, +for the oxygen of the oxide immediately combines with any hydrogen +tending to form on the plate. + +This type of cell has some advantages but also many disadvantages, chief +among which is the fact that the E. M. F. is very low. It is used +principally for railway signal work, slot-machines, etc. + +*A Tomato-Can Battery* using caustic soda as the exciting liquid is a +simple form of home-made battery whose only disadvantage is the low +voltage that it delivers. + +[Illustration: Fig. 67.—A Tomato-Can Cell; Sectional View.] + +[Illustration: Fig. 68.—The Tomato-Can Cell Complete.] + +The cell is liable to polarization, but the large surface of its +positive elements protects it to some extent. + +The positive element and the outer vessel is a tomato can. Within it is +a porous cup made out of blotting paper or unglazed earthenware such as +a flower pot. + +The space between the can and the porous cup is filled with fine +scrap-iron such as borings and turnings. A zinc plate is placed in the +porous cup. + +The cell is filled with a ten-per-cent solution of caustic soda. + +The following table gives the names, elements, fluids, voltage, etc., of +the most useful batteries, all of which may be easily constructed by the +experimenter. + + +Secondary or Storage Batteries + + +The storage battery is a very convenient means of taking energy at one +time or place and using it at some other time or place. + +Small storage batteries are used in automobiles to supply current for +the headlights and spark-coils. Many automobiles are now equipped with +"electric starters," consisting of a dynamo-motor and a storage battery. +Throwing a switch will cause the current from the storage battery to +drive the motor and "crank" the engine. After the engine is started, the +motor acts as a dynamo and generates a current for recharging the +storage battery. + +Storage batteries are also used to drive electric vehicles and cars. + +Many central lighting and power stations employ storage batteries to +supply the extra current demanded during rush hours. In the middle of +the day, when the "load" is light, the surplus current of the dynamos is +used to recharge the storage batteries. + +What is really effected in the storage battery is the electrical storage +of _energy_, not the storage of electricity. Properly speaking, the +energy is put into the form of chemical energy, and there is really _no +more electricity in the cell_ when it is charged than after it is +discharged. + +[Illustration: Fig. 69.—Two Methods of Connecting Cells so as to obtain +Different Voltage and Amperage Values.] + +Storage batteries are made up of plates of lead (the electrodes) or an +alloy of lead cast into a "grid" or framework. + +The framework may be one of a large number of patterns, but usually +consists of a set of bars crossing one another at right angles, leaving +a space between. + +The spaces are filled with a paste of _lead oxide_. They are then +"formed" by placing in a tank of acid solution and connected to a source +of electric current. + +[Illustration: Fig. 70.—Small Storage Cells.] + +The plate connected to the positive wire gradually turns dark-brown in +color, due to the changes in the paste, which gradually turns into _lead +peroxide_. The paste in the negative plate becomes gray in color and +changes into a form of metallic lead called _spongy lead_. + +The positive and negative plates are placed in a bundle after the +forming process has been completed. They are kept apart by strips of +wood or rubber called separators. + +The negative plates of one cell are all connected in parallel at one end +of the cell. The positive plates are connected at the other end. The +liquid surrounding the plates is diluted sulphuric acid. + +When the battery has been exhausted, it is charged by connecting a +dynamo with the terminals of the battery and sending a current through +it. This current reverses the chemical action, which goes on during the +discharge of the battery. + +*A Storage Battery* furnishes the most convenient source of current for +performing all sorts of electrical experiments. It is capable of giving +more current for a longer period than dry cells and is not expensive, +for it merely requires recharging and does not have to be thrown away +each time the current is used up. + +The storage cell described below is made in a very simple manner and +will well repay any time or expense spent in its construction. + +[Illustration: Fig. 71.—How to make the Plates for a Storage Cell.] + +The plates are cut out of a large sheet of lead, one-quarter of an inch +thick. They may be made any convenient size to fit the jars which the +experimenter may have at hand. We will assume that they are to be made +two and seven-eighths inches wide and three and one-half inches long. +They will then fit the rectangular glass storage cell which is already +on the market and can be procured from dealers in electrical supplies. + +A long terminal or lug is left projecting from the plate as shown in +Figure 71. + +Any number of plates may be placed in a single cell, depending of course +upon the size of the glass jar. We will suppose that three will just fit +the jar nicely. An odd number of plates should always be used, so that a +positive plate may come between two negatives. + +Each cell will give two volts regardless of the number of plates. +Increasing the number of plates, however, will give the cell a greater +amperage capacity and make the charge last longer. Three cells (six +volts) will form a convenient set for running small fan-motors, +miniature lights, etc. + +Cut out nine plates and pile them up in sets of three with a piece of +thin wood (cigar-box wood) between each pair of plates. Clamp them +together in a vise and bore full of one-quarter-inch holes. + +The plates are now ready for pasting. They are placed on a smooth slab +of stone or glass and pasted with a stiff mixture of red lead and +sulphuric acid (two parts water to one part acid). The paste must be +pressed carefully into the recesses of the plates with a flat stick. +They are then laid aside to dry and harden. + +[Illustration: Fig. 72.—The Wood Separator.] + +After they have thoroughly dried they should be assembled as in Figure +73 with one positive plate between two negative ones. The wooden +"separators" are easily cut out of wood with a saw and penknife. The +thin wood used in the construction of peach baskets is the best for the +purpose. The separators should be made the same size as the lead battery +plates. + +Each group of plates is then placed in a jar containing a mixture of +sulphuric acid and water (4 parts water to one part acid). In mixing the +acid be very careful to pour the acid into the water, stirring the +mixture slowly at the same time, and not the water into the acid. + +[Illustration: Fig. 73.—The Complete Element for a Storage Cell.] + +The plates are now ready for "forming." The binding-posts on the lugs of +the plates may be secured from the carbons of some old dry cells. The +simplest method of "forming" the plates is to use four gravity cells and +"form" one storage cell at a time. + +[Illustration: Fig. 74.—A Battery of Home-Made Storage Cells.] + +Connect the positive pole (copper) of the gravity battery to the +positive pole (center-plate) of the storage cell and the negative (zinc) +of the gravity battery to the negative (outside plates) of the storage +cell. Allow the current to flow through the storage battery for several +days or until the positive plate turns to a dark chocolate-brown color +and the negatives to a gray-slate. + +[Illustration: Fig. 75.—Gravity Cells. These consist of zinc and copper +elements, immersed in a zinc-copper sulphate solution. They cannot be +easily made, and are best purchased. The illustration also shows the +star-shaped copper and "crowfoot" zinc element used in a gravity cell.] + +After the cells have once been "formed" all that they require is +occasional recharging from gravity cells or from a dynamo, by connecting +the positive pole of the charging current to the positive plates of the +storage cells and the negative pole to the negative plates. + +When the cells are fully charged, bubbles of gas will rise freely from +the plates. If a dynamo is used it must be "_shunt_" wound and not a +"_series_" machine. Recharging will only require about one-quarter of +the time consumed in forming. + +It is a very good plan to connect twelve gravity cells in series and use +them to recharge the storage battery. The gravity cells can always be +kept connected to the storage cells when the latter are not in use and +thus remain fully charged and ready to supply their maximum current. + +After the cells have been in use for some time, it is a good plan to +lift out the plates and remove all sediment which has settled to the +bottom of the jars. + +A set of three such storage cells will have an E. M. F. of over six +volts. Any number may be connected up in series in order to obtain a +higher voltage. + +Storage batteries are usually rated in "ampere hours." An ampere hour is +the amount of current represented by one ampere flowing for one hour. A +ten-ampere-hour storage battery will deliver: + +One ampere for ten hours +Two amperes for five hours +Five amperes for two hours +Ten amperes for one hour + +In other words, the result obtained by multiplying the number of amperes +by the time in hours is the _ampere hour capacity_. + +A dynamo must have an E. M. F. of about ten volts in order to charge a +three-cell storage battery. + + + +CHAPTER V ELECTRO-MAGNETISM AND MAGNETIC INDUCTION + + +Connect two copper wires to a voltaic cell and stretch a portion of the +wire over a compass needle, holding it parallel to it and as near as +possible without touching. Then bring the free ends of the wires +together and observe that the needle is deflected and after a few +movements back and forth comes to rest at an angle with the wire. + +[Illustration: Fig. 76.—A Current of Electricity flowing through a Wire +will deflect a Compass Needle.] + +Next form a rectangular loop of wire and place the needle within it as +in Figure 77. A greater deflection will now be obtained. If a loop of +several turns is formed, the deflection will be still greater. + +These experiments were first performed by Oersted, in 1819, and show +that the region around a wire carrying a current of electricity has +_magnetic_ properties. + +[Illustration: Fig. 77.—If a Loop of Wire is formed about a Compass +Needle, the Deflection will be greater.] + +Another interesting experiment showing the magnetic effect of a current +of electricity when passing through a wire may be performed by +connecting a heavy copper wire to two or three bichromate-of-potash +cells. Dip the wire into a pile of fine iron filings and a thick cluster +of them will adhere to the wire as in Figure 78. + +As soon as the circuit is broken so that the current of electricity +ceases flowing, the filings will fall off, showing that the magnetic +effect ceases with the current. + +[Illustration: Fig. 78.—Iron Filings clustered on a Wire carrying a +Current of Electricity.] + +These three simple experiments have shown that if a current of +electricity is passed through a copper wire, the wire will deflect a +compass needle, attract to itself iron filings, etc., as long as the +current continues to flow. As soon as the current is shut off, the +magnetic effect is _destroyed_. + +The region in the neighborhood of a wire carrying a current is a _field +of force_ through which lines of magnetism are flowing in exactly the +same way that they do in the neighborhood of a bar or horseshoe magnet. + +[Illustration: Fig. 79.—Magnetic Phantom formed about a Wire carrying a +Current of Electricity.] + +This is readily shown by punching a small hole in a piece of cardboard, +and passing a wire carrying a strong current of electricity through the +hole. + +If a few iron filings are sifted on the cardboard and the latter jarred +slightly with a pencil as they fall, they will arrange themselves in +circles with the wire at the center, forming a magnetic phantom and +showing the paths of the lines of magnetic force. + +[Illustration: Fig. 80.—Magnetic Phantom formed about several Turns of +wire.] + +By forming the wire into a coil as in Figure 80 the magnetic field +generated is much stronger and more plainly seen, for then the combined +effect of the wires is secured. + +[Illustration: Fig. 81.—Paper Tube wrapped with Wire for Experimental +Purposes.] + +Roll up a small paper tube about 1/2 inch in diameter and four inches +long. Wind neatly on the tube three layers of No. 18 insulated copper +wire. Pass an electric current through it from two or three cells of a +battery, and test its magnetic properties by bringing it near a compass +needle. It will be found that the coil possesses very marked magnetic +properties, and will readily cause the needle to swing about, even +though it is held quite a distance away. + +If an iron bar is placed inside of the paper tube, the magnetic effect +will be greatly increased. + +[Illustration: Fig. 82.—Showing how the Lines of Force "Leak" at the +sides of the coil, from a Coil of Wire, and how they are concentrated by +an Iron Core.] + +The presence of the iron bar inside of the coil of wire greatly +increases the number of lines of force running through the coil. + +[Illustration: Fig. 83.—The Principle of an Electro-Magnet.] + +When a bar is not used, many of the lines of force leak out at the sides +of the coil, and but few extend from end to end. The effect of the iron +core is not only to diminish the leakage of the lines of force, but also +to add many more to those previously existing. Hence the magnetic +strength of a coil is greatly increased by the iron core. + +A coil of wire wrapped around an iron core forms an _electro-magnet_. + +[Illustration: Fig. 84.—if you wrap some insulated Wire around an +Ordinary Nail and connect it to a Battery, it will become an +Electro-Magnet.] + +If you wrap some insulated wire around an ordinary nail and connect it +to one or two cells of a battery it will become an electro-magnet and +pick up bits of iron and steel. + +If you wind the wire around a small paper tube into which a nail will +slide easily, the coil will draw the nail in when the current is turned +On. A hollow coil of this sort is called a solenoid. + +Electro-magnets and solenoids play a part in the construction of almost +all electrical machinery. They form the essential parts of dynamos, +motors, telephone receivers, telegraph relays and sounders, and a host +of other devices. + +The form usually given to an electro-magnet depends upon the use to +which it is to be put. The horseshoe is the most common. This consists +of two electro-magnets mounted on a yoke and connected so that the two +free poles are North and South. + +[Illustration: Fig. 85.—If you wind the Wire around a small Paper Tube +into which a Nail will slide easily, the Coil will draw the Nail in when +the Current is turned on.] + +Electro-magnets are made on a huge scale for lifting large castings and +heavy pieces of iron. Such magnets are used in the great steel mills and +in factories where nails, bolts, etc., are manufactured. + +Monster electro-magnets can be seen in wonderful perfection at the great +steel mill at Gary, Indiana. + +Ships bring the ore down the lakes to Gary, where great steel jaws lift +it out of the hold of the boat and carry it to the furnaces. + +After being melted, great machines pour it out. It is divided into huge +ingots, and these, while hot, are carried to the first part of the +rolling mill. + +The ingot is squeezed by a machine, made longer and narrower, then +squeezed again and made still longer and narrower. + +It is started on its journey along the rollers of the mill, squeezed and +pressed here and there, as it travels hundreds of yards—no hand ever +touching it. It finally arrives, a red-hot steel rail, the right shape +and the right length. + +During this time the steel has made a long journey and changed from a +shapeless ingot to a finished rail, handled entirely by machinery guided +and controlled by one or two operators, pressing levers and switches. + +When almost finished, the rail slides down an incline before a man who +grasps the rail with huge pinchers, and standing at one end, runs his +eye along it. As he looks along the rail he sees the defects, moves the +left or the right hand, and another man at the levers of the +straightening machine, straightens the rail as directed. + +And soon there are ten rails, perfectly straight, side by side, with +more coming down the incline to meet the glance of the man’s eye. + +They are still too hot for any man’s touch and so a man sitting in a +tower touches an electric switch, and along the overhead rails there +comes gliding a monster electro-magnet. + +The magnet moves along, drops down upon the ten rails, lying side by +side and weighing thousands of pounds. The man in the tower presses +another switch, thus turning on the current, and electricity glues the +rails to the magnet. + +[Illustration: _By permission, from "Solenoids" by C. R. Underhill._ +Lifting-Magnets of the type known as Plate, Billet, and Ingot Magnets.] + +The ten rails are lifted at once, as easily as you would lift a needle +with your horseshoe magnet; they are carried to a flat-car, and when +lowered in position, the current is turned off, releasing the rails, and +the magnet travels back for another load. + + +Induction + + +In 1831, Michael Faraday, a famous English chemist and physicist, +discovered that if a magnet be suddenly plunged into a hollow coil of +wire, a momentary current of electricity is generated in the coil. As +long as the magnet remains motionless, it induces no current in the +coil, but when it is moved back and forth, it sets up the currents. The +source of electrical energy is the mechanical work done in moving the +magnet. + +[Illustration: Fig. 86.—Showing how a Current of Electricity may be +induced by a Bar Magnet and a Coil.] + +The medium which changes the mechanical energy into electricity is the +magnetic field which we have already seen exists in the neighborhood of +a magnet. + +A current of electricity produced in a coil in such a manner is said to +be an _induced_ current and the phenomenon is that known as _magnetic +induction_. + +Magnetic induction is met in the dynamo, induction coil, telephone, +transformer, some forms of motors, and a number of other electrical +devices. + +[Illustration: Fig. 87.—A Horseshoe Magnet and a Coil arranged to +produce Electric Currents by _Induction_.] + +A simple experiment in which electricity is produced by magnetic +induction may be performed by winding a number of turns of fine +insulated wire around the armature or keeper of a horseshoe magnet, +leaving the ends of the iron free to come in contact with the poles of +the permanent magnet. Connect the ends of the coil to a sensitive +galvanometer,¹ the ends of the armature being in contact with the poles +of the horseshoe magnet as shown in Figure 87. + +Keeping the magnet fixed, suddenly pull off the armature. The +galvanometer will show a momentary current. Suddenly bring the armature +up to the poles of the magnet; another momentary current in the reverse +direction will flow through the circuit. + +The fact that it is a reverse current is shown by the actions of the +galvanometer for it will be noticed that the needle swings in the +opposite direction this time. + +It will also be noticed that no current is produced when the coil and +magnet are stationary. Current is only generated when the coil and +magnet are approaching one another or moving apart suddenly. + +This is because it is only then that the magnetic field is changing. The +field is strongest nearest the magnet, and therefore if either the +magnet or the coil of wire is moved, the strength of that part of the +field which intersects the coil is changed. Induced currents can only be +generated by a _changing_ magnetic field. + + ¹ See chapter on Measuring Instruments. + + + +CHAPTER VI ELECTRICAL UNITS + + +The Ampere + + +There are certain terms used in the electrical field to distinguish +various properties and qualities of the electrical current with which it +is well for the young experimenter to acquaint himself. + +One of the first units usually required, in order to make intelligent +comparisons, is a unit of measure. The _quart_ is the unit of _measure_ +commonly applied to liquids and is based upon the amount of space +occupied by a certain volume. The _pound_ is a unit of weight which +determines a certain amount of any substance by comparing the force +which gravity exerts in pulling it to the earth with the same effect of +gravity on another standard "weight." + +Electric current is invisible and weightless, and for these and other +reasons cannot be measured by the quart or weighed by the pound. The +only way that it can be measured is by means of some of the effects +which it produces. Either the chemical, electro-magnetic, or the heating +effects may be made the basis of a system of measurement. + +The first method used to measure electric current was the chemical one. + +If a current is passed through a solution of a chemical called copper +_sulphate_ (blue vitriol) by means of two copper plates, _copper_ will +be deposited on one plate and dissolved from the other. If the current +is furnished by a battery the copper will be deposited on the plate +connected with the zinc of the battery. If the current is allowed to +flow for a short time and the two copper plates are then taken out and +weighed it will be found that one plate is considerably heavier than the +other. + +The copper has been taken from one plate and deposited on the other by +the _electric currents_. The amount of electric current which will +deposit 1.177 grammes of copper in an hour is called an _ampere_. The +ampere is the unit of electrical current measurement, and implies +quantity or amount. + +The chemical method of measuring current was at one time put to +practical service in the distribution of electric current for lighting +and power. Many years ago the house meters, used to measure the current, +consisted of a jar containing two copper plates. The current used in the +house would cause copper to deposit on one plate, and by weighing the +plate the power company could determine the amount of current used, and +thereby the amount of the bill. The meters nowadays make use of the +magnetic effects of the current instead of the chemical, as described +later on. + + +The Volt + + +For purposes of explanation the electric current may be likened to a +stream of water flowing through a pipe. + +If you hold your thumb over the end of a water-pipe through which water +is flowing it will push your thumb away because of the _pressure_ which +the water exerts. + +Electric currents also exert a _pressure_, only it is not called +pressure in electrical parlance, but, spoken of as _electromotive force_ +or _potential_. + +The pressure of the water enables it to pass through small openings and +to overcome the resistance offered by the pipe. + +Wires and other electrical conductors do not offer a perfectly free path +to an electric current, but also possess a resistance. It is the +potential of the electro-motive force which overcomes the resistance and +pushes the current through the wire. + +Advantage has been taken of the fact to fix a unit of electrical +pressure called the _volt_. The pressure of the water in a water-pipe is +measured in pounds, but the pressure of an electric current in a wire is +measured by _volts_. The volt is the unit of electrical force which will +cause a current of one ampere to flow through a resistance of one _ohm_. + + +The Ohm + + +The ohm is the unit of electrical resistance. The standard ohm is the +resistance offered by a column of pure mercury having a section of one +square millimeter and a length of 106.28 centimeters at a temperature of +0° centigrade. + +The pressure which will force sufficient current through such a column +of mercury to deposit 1.177 grammes of copper in one hour is a volt, and +in doing so has passed a current of one ampere through a resistance of +one ohm. + +The units ohm, ampere, and volt, were named in honor of the three great +electricians: Ohm, Ampère, and Volta. + +These three units bear a very close relation to each other which is +explained by Ohm’s Law. + +Ohm’s Law is a simple statement of facts which it is well for the young +electrician thoroughly to understand, for it might almost be said to be +the basis of design of almost all electrical instruments. + +It is simply this: The strength of a current equals the voltage divided +by the resistance. It may be expressed in symbols by: _C = E/R_. Where C +is the current in amperes, E is the potential in volts, and R the +resistance in ohms. + +By way of a simple example, we will suppose that a small telegraph +sounder is connected to a battery and that the voltage of the battery is +_ten volts_. We will further suppose that the resistance of the sounder +connecting wires and the battery itself is _five ohms_. Knowing these +two facts, it is very easy to find out how many amperes are flowing +through the sounder by substituting these values in the equation as +follows: + +C = E/R +E = 10 volts and R = 5 ohms +therefore C = 10/5 or 2 amperes + +In order to indicate fractions or very large values of the ampere, volt, +and ohm, it is customary to use the following terms: + +Milli-volt = 1/1000 of a volt +Mill-ampere = 1/1000 of an ampere +Kilo-volt = 1000 volts +Meg-ohm = 1,000,000 ohms + + +The Watt + + +It is no doubt perfectly plain that the water in a certain size of pipe +at a pressure of 100 lbs. is more powerful than a stream of water in the +same size of pipe at 25 lbs. pressure. + +Likewise a current of electricity represents more power at 100 volts +potential than the same current would at 25 volts. The unit of +electrical power is called the _watt_. A watt is represented by a +current of one ampere flowing through a wire at a potential of one volt. + +The number of watts is found by multiplying the voltage by the amperage. +In the case of the sounder and battery used as an example to explain +Ohm’s Law, and where the voltage was 10 and the amperage found to be 2, +the number of watts is 10 x 2, or 20 watts. + +Seven hundred and forty-six watts represent one electrical horse-power. +One thousand watts are called a _kilo-watt_. + + +The Coulomb + + +So far, none of the units have taken into consideration the element of +time. + +If water should be permitted to run out of a pipe into a tank until ten +gallons had passed it would not be possible to tell at what rate the +water was flowing by knowing that ten gallons had passed unless it were +also known how long the water had been flowing. Ten gallons per minute +or ten gallons per hour would indicate the rate of flow. + +One ampere flowing for one second is the electrical unit of flow. This +unit is called the _coulomb_. + +One ampere flowing for one hour is called an _ampere hour_. The number +of ampere hours is found by multiplying the current in amperes by the +time in hours. + +A battery may be said to have a capacity of 10 ampere hours. This means +that it will deliver one ampere for 10 hours (1 ampere x 10 hours = 10 +ampere hours) or 2 amperes for 5 hours (2 amperes x 5 hours = 10 ampere +hours). + +The same element of time enters into consideration in connection with +the watt. One watt flowing for one hour is a _watt hour_ and one +kilowatt flowing for one hour is a _kilo-watt hour_. + + +The Difference between Alternating and Direct Currents + + +There are two distinct kinds of electric current supplied for lighting +and power, one known as _direct_ current and the other as _alternating_. + +A _direct current_ is one which passes in one direction only. It may be +represented by a straight line, as _A_ in Figure 88. + +An alternating current is one which reverses its direction and passes +first one way and then the other. It may be represented by a curved +line, shown in Figure 88. It starts at _zero_, and gradually grows +stronger and stronger. Then it commences to die away until no current is +flowing. At this point it reverses and commences to flow in the opposite +direction, rising gradually and then dying away again. + +This is repeated a definite number of times per second; when the current +rises from zero, reverses and returns to zero, it is said to pass +through a _cycle_. + +[Illustration: Fig. 88.—Graphic Representation of a Direct and an +Alternating Current.] + +The part of the curved line from _a_ to _b_ in Figure 88 represents the +first part of the current, when it is rising. From _b_ to _c_ represents +its fall. The point at which the curved line crosses the straight line +is zero. At _c_ the current crosses the line and commences to flow in +the opposite direction until it reaches _d_, at which point it dies away +and again crosses the line to flow in its original direction and _repeat +the cycle_. + +In electrical parlance, that part of the current from _a_ to _c_ or from +_c_ to _e_ is known as an _alternation_. From _a_ to _e_ is called a +cycle. + +The reason why alternating current is often used in place of direct +current is that it can be sent over the wires for long distances more +economically than direct current. This is more fully explained farther +on in the chapter dealing with a step-down transformer. + +The number of _cycles_ taking place in one second is known as the +_frequency_ of the current. The usual _frequency_ of commercial +alternating currents is 60 cycles per second or 7200 alternations per +minute. + + + +CHAPTER VII ELECTRICAL APPURTENANCES + + +Wires + + +Electric currents are usually led from place to place, at will, by means +of conductors called _wires_. There are a great many kinds of wires, +each adapted to some special purpose. + +Wires are usually covered with a material called an _insulator_, in +order to prevent the loss of electric current due to the wires coming +into contact with other bodies or circuits. Insulators are substances +which do not conduct electricity. + +Wires which are _insulated_ by heavy braids of cotton fiber and then +impregnated with some compound, such as creosote, are called +_weather-proof_ wires, and are best adapted to outside service, where +they must be exposed to the action of the elements. + +The wires used for interior wiring in buildings, etc., are usually +insulated with rubber, over which is placed a cotton braid to protect +the rubber. + +Rubber cannot well be used as an insulator for all wires, although its +insulating value is very great, owing to the fact that it deteriorates +under many conditions. + +Rubber-covered and weather-proof wires are made in a variety of +insulations. Some may have only one insulating layer, while others have +a great many. Different substances are used as insulators to adapt the +wire to some special purpose. Copper is usually the only metal used to +form the wire or conductor itself. The reason for this is that copper is +a better conductor than any other metal except those known as precious +metals, such as gold and silver, the cost of which prohibits their use +for such purposes. The wire may be solid, or made up of a number of +small conductors so that it is flexible. + +The various combinations of insulating layers, together with either a +solid or a stranded conductor, have made possible a variety of +current-carriers, known as: + +Theater or Stage Cable +Elevator Cable +Fixture Wire +Telephone Wire +Mining Cable +Feeder Cable +Brewery Cord +Heater Cord, etc. + +depending upon the special use for which they were designed. + +The wires which the young experimenter is likely to use in his work the +most are known as _magnet wires_, and are used for making +electro-magnets, coils, and various windings. Magnet wires may be +insulated with either silk, cotton, or enamel. + +Silk-covered and cotton-covered wires may be obtained with either a +single or double covering. + +Wires with a single covering of silk or enamel are used when it is +desirable to save space, for the covering of these two classes of magnet +wires is thinner than either the cotton or double-silk-covered wire, and +consequently they require less room for winding. + +The size of the wire is indicated by its diameter, and in the United +States is measured by the Brown and Sharpe gauge, often indicated by the +term, "B. & S." + +The preceding table shows the various sizes of wire of the Brown and +Sharpe gauge, and also several of their characteristics, such as weight, +resistance, etc. + + +Insulators + + +The covering placed over wires is not the only precaution taken to +insulate them, but in the case of permanent wiring they are usually +mounted on glass or porcelain supports. + +[Illustration: Fig. 89.—Staples and Wooden Cleat used for running Low +Voltage Wires.] + +Wires used for batteries, bells, telephones, etc., operated by batteries +and where the voltage is not over 20 volts, may be run under _insulated_ +staples or wooden cleats inside of a building. If outside and exposed to +the weather, they should be mounted on suitable glass or porcelain +knobs. + +[Illustration: Fig. 90.—Porcelain Insulators to support Electric Light +Wires.] + +Electric-light wires for inside use are commonly supported by insulators +made of porcelain and known as cleats, knobs, and tubes according to the +shape. + +Telegraph, telephone, and power lines are usually supported by glass +knobs or large porcelain insulators which screw on to wooden pins. + +[Illustration: Fig. 91.—Glass Insulator Binding-Posts and Pin used to +support Telegraph and Telephone wires.] + + +Binding-Posts + + +Binding-posts are the most convenient device to make quick connections +between wires and other parts of electrical apparatus. + +Binding-posts may be either made or purchased. Those which are purchased +are of course the best, and will add greatly to the appearance of any +instrument upon which they are mounted. + +Several of the best-known types of manufactured posts are shown in +Figure 92. + +[Illustration: Fig. 92.—Types of Binding-Posts.] + +Figure 93 shows different ways of making simple binding-posts and +connectors from screws, washers, screw-eyes, and strips of metal. The +drawings are self-explanatory and should need no comment. + +[Illustration: Fig. 93.—Home-made Binding-Posts.] + +The screws and nuts obtainable from old dry cells are very convenient to +use for binding-posts and other similar purposes. + + +Switches and Cut-Outs + + +Switches and cut-outs are used in electrical work for turning the +current on and off. + +If the experimenter chooses to make them himself, care should be taken, +to construct them in a strong and durable fashion, for they usually are +subjected to considerable use, with consequent wear and tear. + +[Illustration: Fig. 94.—Binding-Post removed from the Carbon of a Dry +Cell.] + +Several very simple home-made switches are illustrated in Figure 95. + +[Illustration: Fig. 95.—Simple Switches. _A_, Single-Point Switch. _B_, +Two-Point Switch. _C_, Three-Point Switch. _D_, Five-Point Switch. _E_, +Lever with End Rolled up to form Handle. _F_, Lever with Handle made +from part of a Spool.] + +The first one shown (_A_) has one contact, formed by driving a +brass-headed tack through a small strip of copper or brass. + +The movable arm is a strip of copper or brass, rolled up to form a +handle at one end. The other end is pivoted with a brass screw. The +brass screw passes through a small strip of copper or brass having a +binding-post mounted on the end. A small copper washer should be placed +between the movable arm and the copper strip to make the switch work +more easily. + +A somewhat similar switch is shown by _B_ in the same illustration, only +in this case a handle made from half of a spool is used, instead of +rolling up the end of the arm. + +The other illustrations show how the same method of construction may be +applied to make switches having more than one "point" or contact. + +No dimensions have been given for constructing these switches, because +it is doubtless easier for the young experimenter to use materials which +he may have at hand, and construct a switch of his own proportions. Only +one suggestion is necessary, and that is to bevel the under edges of the +arm with a file, so that it will slip over the head of the brass tack +more easily. + +The switches shown in Figure 96 are capable of carrying heavier currents +than those just described, and more nearly approach the type used on +lighting and power switchboards. + +The base may be made of wood, but preferably should be made of some +insulating substance such as fiber or slate. + +[Illustration: Fig. 96.—Knife Switches.] + +The patterns for the metal parts are shown in Figure 97. These are cut +from heavy sheet-brass or sheet-copper, and then bent into shape with a +pair of flat-nosed pliers. + +The handle of the single-pole switch is driven on over the metal tongue. + +The double-pole switch is almost a duplicate of the single-pole type, +but has two sets of levers and contacts, actuated by the handle, in +place of one. + +[Illustration: Fig. 97.—Metal Parts for the Knife Switches.] + +The ends of the blades to which the handle is connected are turned over +at right angles and a hard-wood cross-bar fastened between the ends. The +handle is fastened to the center of the cross-bar. + +After the switch is assembled, bend the various parts until they "line +up" that is, are in proper position in respect to each other, so that +the blades will drop into the contacts without bringing pressure to bear +on either one side or the other of the handle in order to force the +blades into line. + + +Fuses + + +Fuses are used to prevent electrical instruments and wires from damage +due to too much current flowing through. When an electric current passes +through a resistance it produces _heat_. + +A fuse is usually a short piece of lead or some alloy which melts at a +low temperature, and which is inserted in the circuit so that the +current must flow through it. If too much current flows through the fuse +it will become hot and melt, because of its low melting-point, thus +interrupting the circuit and shutting the current off until the cause +which occasioned the surplus current to flow can be ascertained. + +Fuses are rated according to the amount of current which is required to +"blow" them out, and therefore are called 1, 3, 5, or 10 ampere fuses, +as the case may be. + +[Illustration: Fig. 98.—Simple Fuses. _A_, Fuse-Block with plain Wire +Fuse. _D_, Fuse-Block with Mica Fuse in position.] + +When a fuse burns out in a trolley car or in a light or power circuit, +it is because a greater amount of current is trying to pass than the +circuit can safely carry. If a fuse were not placed in such a circuit so +as to shut the current off before the danger point is reached, any +electrical device might become "burned out," or in extreme cases, the +wires become so hot as to cause a serious fire. + +Figure 98 shows several simple forms of fuses which the experimenter may +easily make to protect the batteries, etc., from short circuits. + +The simplest possible fuse consists merely of a small piece of lead wire +or a strip of thick tinfoil held between two binding-posts mounted upon +a wooden block. + +The same form of fuse may be made from a strip of mica about two and +one-half inches long and one-half an inch wide. + +A strip of thin sheet-copper is bent around the ends of the mica strip. + +A piece of fuse wire is stretched between the two copper contacts and +fastened to each with a drop of solder. Fuse wire of any desired +ampere-carrying capacity can be obtained from most electrical supply +houses. + +Such a fuse is held in a mounting as shown by _D_. The contacts are made +from sheet-copper or brass. They should spring together very tightly, so +as to make perfect contact with the copper ends on the mica strip. + + +Lightning-Arresters + + +Lightning-arresters are used to protect all wires which run into a +building from outdoors, especially telegraph or telephone wires, so that +static electricity due to lightning will not damage the instruments. + +Lightning-arresters may be constructed in many ways and of different +materials, but there are only two types for which the average +experimenter will have any use. + +[Illustration: Fig. 99.—Lightning-Arrester and Ground-Wire Switch.] + +The arrester shown in Figure 99 is the type known as "lightning-arrester +and ground-wire switch." It is used principally on telegraph lines. + +It consists of three pieces of sheet-brass about one-sixteenth of an +inch thick, and shaped as shown by _A_, _B_, and _C_ in Figure 100. + +The metal pieces are mounted on a wooden block with a narrow space of +about one-thirty-second of an inch separating them. + +[Illustration: Fig. 100.—Home-made Lightning-Arrester.] + +The two outside pieces are each fitted with two binding-posts, and the +center triangular-shaped piece is fitted with one post. + +A hole about one-eighth of an inch in diameter is bored between each of +the metal pieces. + +Make a tapered metal pin which can be placed tightly in the holes, and +will make contact between the metal pieces. + +The two outside line wires of the telegraph circuit are connected to the +outside metal pieces _C_ and _B_. _A_ is connected to the earth or +ground. + +In case of a lightning storm, if the wires become charged, the small +space between the metal plates will permit the charge to jump across and +pass harmlessly into the ground. + +If complete protection is desired, it is merely necessary to insert the +plug in one of the holes, and thus "ground" either wire or short-circuit +both of them. + +[Illustration: Fig. 101.—Lightning-Arrester for Telephone Wires.] + +The lightning-arrester shown in Figure 101 is designed for service on +telephone wires. It is an ordinary fuse provided with an arrester in the +shape of two carbon blocks about one inch square. The blocks rest on a +copper strip, and are held in place by a spring-strip connected to _B_. + +The carbon blocks are separated by a piece of thin sheet-mica, of the +same size as the blocks. + +The post, _B_, is connected to one of the telephone-line wires near the +point where it enters the building from outdoors. The post, _A_, is +connected to the instrument; _C_ is connected to the ground. + +An arrester of this kind should be connected to each one of the +telephone wires. + +If the line wires should happen to come into contact with a power wire, +there is danger of damage to the instruments, but if an arrester is +connected in the circuit such an occurrence would be prevented by the +blowing out of the fuse. If the lines become charged by lightning, the +charge can easily pass over the edge of the mica between the two blocks +and into the ground. + + + +CHAPTER VIII ELECTRICAL MEASURING INSTRUMENTS + + +An instrument designed to measure electromotive force (electrical +pressure) is called a _voltmeter_. An instrument designed to measure +volume of current is called an _ammeter_. + +There are many forms of reliable meters for measuring current and +voltage, but all are more or less expensive and out of the reach of an +ordinary boy. + +Some meters are more carefully made than a watch, and are provided with +fine hair-springs and jeweled bearings, but all depend upon the same +principle for their action, namely, the mutual effects produced between +a magnetic needle and a coil of insulated wire carrying a current of +electricity. + +The little meters described in this chapter are simple and inexpensive +but quite sensitive. Unlike a meter making use of a hair-spring, they +will stand considerable rough handling, but of course should not be +subjected to such treatment unnecessarily. + +Two types of meters are described. Both operate on exactly the same +principle, but one is more elaborate than the other. + + +A Simple Voltmeter and Ammeter + + +A base-board five inches long, two and one-half inches wide and one-half +inch thick is cut out of hard wood. In its center, cut a slot +three-eighths of an inch wide and one and one-half inches long, with the +slot running lengthwise the board. Along each side of the slot glue two +small wooden blocks one and one-half inches long, one-quarter of an inch +thick, and one-half of an inch high. + +[Illustration: Fig. 102.—_A_, Base, showing Slot. _B_ and _C_, Sides and +Top of the Bobbin. _D_, Base and Bobbin in Position.] + +When they are firmly in position, glue a strip of wood, two and one-half +inches long, three-quarters of an inch wide and one-eighth inch thick to +the top as shown by D in Figure 102. + +Using these as a support, wind a horizontal coil composed of 200 feet of +No. 36 B. & S. gauge silk-covered wire. + +A needle is next made from a piece of watch-spring. It should be about +one and one-quarter inches long, and one-eighth of an inch wide. + +Straighten it out by bending, and then heat the center in a small +alcohol flame until the center is red-hot, taking care to keep the ends +as cool as possible. + +The spring is mounted on a small steel shaft made by breaking up an +ordinary sewing-needle. Make the piece one-half of an inch long. It must +have very sharp points at both ends. The ends may be pointed by +grinding. + +[Illustration: Fig. 103.—Arrangement of the Needle and Pointer.] + +Bore a small hole just large enough to receive the needle through the +center of the spring. Insert the needle in the hole and fasten it in the +center by two small circular pieces of wood which fit tightly on the +needle. A little glue or sealing-wax will serve to help make everything +firm. + +The pointer is a piece of broom-straw, about three inches long. Bore a +small hole in the top of one of the wooden clamps and insert the pointer +in the hole, fastening it with a little glue. The pointer should be +perfectly straight, and in a position at right angles to the spring. + +Bore a small hole in the bottom of one of the wooden clamps and glue a +small wire nail in the hole. The purpose of the nail is to serve as a +counterweight and keep the pointer in a vertical position. + +The spring should be magnetized by winding ten or twelve turns of magnet +wire around one end and connecting it with a battery for a moment. + +[Illustration: Fig. 104.—_A_, Bearings. _B_, How the Needle is mounted.] + +The needle is mounted in two small pieces of thin sheet-brass, one inch +long and one-half inch wide. Bend each strip at right angles in the +middle, and at one-quarter of an inch from one end make a small dent by +means of a pointed nail and a hammer. + +The strips are now slipped down in the center of the slot in the coil +with the dents inside of the coil and exactly opposite one another. +After the exact position is found, they may be fastened into position by +two very small screws. + +The sharp-pointed sewing-needle, together with the magnetized spring, +pointer, and counterweight, should slip down into the dents made in the +strips and swing freely there. It may require a little filing and +bending, but the work should be done patiently, because the proper +working of the meter will depend upon having the needle swing freely and +easily in its place. + +Fasten an upright board, four inches wide and one-quarter of an inch +thick, to the base-board, back of the bobbin. + +Attach a piece of thick cardboard to the upright by means of small +blocks, in such a position that the pointer swings very close to it but +does not touch it. + +The meter is now complete, except for marking or calibrating the scale. +The method of accomplishing this will be described farther on. + +[Illustration: Fig. 105.—The Completed Meter.] + +If the meter is wound with No. 36 B. & S. gauge wire it is a voltmeter +for measuring voltage. If it is wound with No. 16 B. & S. gauge wire it +will constitute an ammeter for measuring amperes. + + +A Portable Voltmeter and Ammeter + + +The bobbin upon which the wire is wound is illustrated in Figure 106. +The wood is the Spanish cedar, of which cigar boxes are made. It should +be one-eighth of an inch thick, and can be easily worked with a +pocket-knife. In laying out the work, scratch the lines on the wood with +the point of a darning-needle. Pencil lines are too thick to permit of +accuracy in small work. The bobbin when finished must be perfectly true +and square. + +The dimensions are best understood from the illustrations. In putting +the bobbin together, do not use any nails. Use strong glue only. + +Two bobbins are required, one for the ammeter and one for the voltmeter. +After completing the bobbins, sandpaper them and coat them with shellac. + +[Illustration: Fig. 106.—Details of the Bobbin.] + +The bobbin for the ammeter is wound with No. 14 B. & S. +double-cotton-covered magnet wire. The voltmeter requires No. 40 B. & S. +silk-covered wire. In both cases the wire should be wound carefully in +smooth, even layers. A small hole is bored in the flange through which +to pass the end of the wire when starting the first layer. After +finishing the winding, about six inches of wire should be left at both +ends to make connection with the terminals. The whole winding is then +given a coat of shellac. A strip of passe-partout tape, one-half of an +inch wide wound over the wire around the bobbin will not only protect +the wire from injury, but also give the bobbin a very neat appearance. + +The armature is a piece of soft steel one inch long, one-eighth of an +inch thick and three-eighths wide. A one-eighth-inch hole is bored +one-sixteenth of an inch above the center for the reception of the +shaft. The center of gravity is thus thrown below the center of the mass +of the armature, and the pointer will always return to zero if the +instrument is level. + +The shaft is a piece of one-eighth-inch Bessemer steel rod, +seven-sixteenths of an inch long. The ends are filed to a sharp +knife-edge on the under side, as indicated in the figure. + +[Illustration: Fig. 107.—The Bobbin partly cut away so as to show the +Bearing. Details of the Armature and Shaft.] + +A one-sixteenth-inch hole is bored in the top of the armature to receive +the lower end of the pointer, which is a piece of No. 16 aluminum wire, +four and one-half inches long. + +After the holes have been bored, the armature is tempered so that it +will retain its magnetism. It is heated to a bright red heat and dropped +into a basin of strong salt water. The armature is then magnetized by +rubbing one end against the pole of a strong magnet. + +The bearings are formed by two strips of thin sheet-brass, +three-sixteenths of an inch wide, and one and one-quarter inches long, +bent and glued to the sides of the bobbin. + +In the illustration, part of the bobbin is represented as cut away. The +center of the bearing is bent out so that the end of the shaft will not +come in contact with the sides of the bobbin. The top of the center is +notched with a file to form a socket for the knife-edges of the shaft. + +[Illustration: Fig. 108.—Completed Voltmeter.] + +The bobbin is glued to the center of a wooden base, seven inches long, +four inches wide and three-quarters of an inch thick. The terminals of +the coil lead down through two small holes in the base and thence to two +large binding-posts. The wires are inlaid on the under side of the base, +i.e., they pass from the holes to the binding-posts through two grooves. +This precaution avoids the possibility of their becoming short-circuited +or broken. + +The case is formed of two sides, a back and top of one-half-inch wood. +It is six inches high, four inches wide, and two inches deep. A glass +front slides in two shallow grooves cut in the wooden sides, one-eighth +of an inch from the front. + +The case is held down to the base by four round-headed brass screws, +which pass through the base into the sides. It is then easily removable +in case it ever becomes necessary to repair or adjust the instrument. + +The meter and case, as illustrated in Figure 108, are intended for +portable use and are so constructed that they will stand up. A small +brass screw, long enough to pass all the way through the base, serves to +level the instrument. If a little brass strip is placed in the slot in +the screw-head and soldered so as to form what is known as a "winged +screw," the adjustment may be made with the fingers and without the aid +of a screw-driver. + +Where the instrument is intended for mounting upon a switch-board, it +can be given a much better appearance by fitting with a smaller base, +similar in size and shape to the top. The binding-posts are then mounted +in the center of the sides. + +To calibrate the meters properly, they are compared with some standard. +The scale is formed by a piece of white cardboard glued by two small +blocks on the inside of the case. The various values are marked with a +pen and ink. The glass front, therefore, cannot be put in place until +they are located. + +The zero value on the meters will normally be in the center of the +scale. When a current is passed through the bobbin, the armature tends +to swing around at right angles to the turns of wire. But since the +armature is pivoted above the center of the mass, when it swings, the +center of gravity is displaced and exerts a pull in opposition to that +of the bobbin, and the amount of swing indicated by the pointer will be +greater as the current is stronger. The pointer will swing either to the +right or the left, depending upon the direction in which the current +passes through the bobbin. The pointer of the instrument illustrated in +Figure 108 is at zero when at the extreme left of the scale. The pointer +is bent to the left, so that the current will be registered when passing +through the meter only in one direction, but the scale will have a +greater range of values. It will also be necessary to cut a small groove +in the base of the instrument in this case so that the armature will +have plenty of room in which to swing. + +[Illustration: Fig. 109.—Circuits for Calibrating the Ammeter and +Voltmeter.] + +When calibrating the ammeter, it is placed in series with the standard +meter, a set of strong batteries, and a rheostat. The rheostat is +adjusted so that various current readings are obtained. The +corresponding positions of the pointer on the meter being calibrated are +then located for each value. + +The voltmeters must be placed in parallel, or shunt with each other, and +in series with several battery cells. A switch is arranged so that the +voltage of a varying number of cells may be passed through the meters. +To secure fractional values of a volt, the rheostat is placed in shunt +with the first cell of the battery. Then, by adjusting both the switch +and the rheostat, any voltage within the maximum range of the battery +may be secured. + +This means of regulating voltage is a common one, and of much use in +wireless telegraph circuits, as will be explained later. + +When using the meters, it is always necessary that the ammeter shall be +in series and the voltmeter in parallel or in shunt with the circuit. + + +Galvanoscopes and Galvanometers + + +In the first part of Chapter V it was explained that several turns of +wire surrounding a compass-needle would cause the needle to move and +show a deflection if a current of electricity were sent through the +coil. + +Such an instrument is called a _galvanoscope_ and may be used for +detecting very feeble currents. A galvanoscope becomes a _galvanometer_ +by providing it with a scale so that the deflection may be measured. + +A galvanometer is really, in principle, an ammeter the scale of which +has not been calibrated to read in amperes. + +[Illustration: Fig. 110.—Simple Compass Galvanoscope.] + +A very simple galvanoscope may be made by winding fifty turns of No. 36 +B. & S. gauge single-silk-covered wire around an ordinary pocket +compass. The compass may be set in a block of wood, and the wood +provided with binding-posts so that connections are easily made. + +Another variety of the same instrument is shown in Figure 111. + +[Illustration: Fig. 111.—Galvanoscope.] + +Wind about twenty-five turns of No. 30 B. & S. gauge cotton-covered +wire around the lower end of a glass tumbler. Leave about six inches of +each end free for terminals, and then, after slipping the coil from the +glass, tie the wire with thread in several places so that it will not +unwind. Press two sides of the coil together so as to flatten it, and +then attach it to a block of wood with some hot sealing-wax. + +Make a little wooden bridge as shown in Figure 111, and mount a +compass-needle on it in the center. The compass-needle may be made out +of a piece of spring-steel in the manner already described in Chapter I. + +Mount two binding-posts to the corners of the block, and connect the +ends of the wire coil to them. Turn the block so that the needle points +North and South and parallel to the coil of wire. + +If a battery is connected to the binding-posts, the needle will fly +around to a position at right angles to that which it first occupied. + +An astatic galvanoscope is one having two needles with their poles in +opposite directions. The word "astatic" means having no directive +magnetic tendency. If the needles of an astatic pair are separated and +pivoted separately, they will each point to North and South in the +ordinary manner. But when connected together with the poles arranged in +opposite directions they neutralize each other. + +An astatic needle requires but very little current in order to turn it +either one way or the other, and for this reason an astatic galvanoscope +is usually very sensitive. + +A simple instrument of this sort may be made by winding about fifty +turns of No. 30-36 B. & S. gauge single-silk or cotton-insulated wire +into a coil around a glass tumbler. After removing the coil from the +glass, shape it into the form of an ellipse and fasten it to a small +base-board. + +Separate the strands of wire at the top of the coil so that they are +divided into two groups. + +[Illustration: Fig. 112.—Astatic Galvanoscope.] + +Make a bridge or standard in the shape of an inverted U out of thin +wooden strips and fasten it to the block. + +The needles are ordinary sewing-needles which have been magnetized and +shoved through a small carrier-bar, made from a strip of cardboard, with +their poles opposite one another, as shown in the illustration. + +[Illustration: Fig. 113.—Astatic Needles.] + +They may be held in place in the cardboard strip by a small drop of +sealing-wax. + +A small hole is punched in the top of the carrier, through which to pass +the end of a thread. The upper end of the thread passes through a hole +in the bridge and is tied to a small screw-eye in the center of the +upper side of the bridge. + +The carrier-bar is passed through the space where the coil is split at +the top. The lower needle should hang in the center of the coil. The +upper needle should be above and outside the coil. + +The terminals of the coil are connected to two binding-posts mounted on +the base-block. + +Owing to the fact that this galvanoscope is fitted with an astatic +needle, the instrument does not have to be turned so that the coil may +face North and South. The slightest current of electricity passing into +the coil will instantly affect the needles. + +An astatic galvanometer for the detection of exceedingly weak currents +and for use in connection with a "Wheatstone bridge" for measuring +resistance, as described farther on, will form a valuable addition to +the laboratory of the boy electrician. + +Make two small bobbins similar to those already described in connection +with the volt and ammeter, but twice as long, as shown in Figure 114. + +Wind each of the bobbins in the same direction with No. 36 silk-covered +or cotton-covered wire, leaving about six inches free at the ends for +connection to the binding-posts. + +Fasten each of the bobbins to the base-board with glue. Do not nail or +screw them in position, because the presence of nails or screws may +impair the sensitiveness of the instrument. In mounting the bobbins, +leave about one-sixteenth of an inch of space between the inside +flanges, through which the needle may pass. + +Connect the coils wound on the bobbins so that the end of the outside +layer of the first coil is connected to the inside layer of the other +coil. This arrangement is so that the current will travel through the +windings in the same continuous direction, exactly the same as though +the bobbin were one continuous spool. + +[Illustration: Fig. 114.—Bobbin for Astatic Galvanometer.] + +Magnetize two small sewing-needles and mount them in a paper stirrup +made from good, strong paper, as shown in Figure 114. Take care that the +poles are reversed so that the north pole of one magnet will be on the +same side of the stirrup as the south pole of the other. They may be +fastened securely by a drop of shellac or melted sealing-wax. + +Cut out a cardboard disk and divide it into degrees as in Figure 115. +Glue the disk to the top of the bobbins. A small slot should be cut in +the disk so that it will pass the lower needle. + +A wooden post should be glued to the back of the base. To the top of +this post is fastened an arm from which are suspended the magnetic +needles. + +A fine fiber for suspending the needle may be secured by unraveling a +piece of embroidery silk. + +[Illustration: Fig. 115.—Completed Astatic Galvanometer.] + +The upper end of the fiber is tied to a small hook in the end of the +arm. The wire hook may be twisted so that the needles may be brought to +zero on the scale. Zero should lie on a line parallel to the two coils. + +The fiber used for suspending the needles should be as fine as possible. +The finer the fiber is, the more sensitive will the instrument be. + +The lower needle should swing inside of the two coils, and the upper +needle above the disk. + + +How to Make a Wheatstone Bridge + + +The amateur experimenter will find many occasions when it is desirable +to know the resistance of some of his electrical apparatus. Telephone +receivers, telegraph relays, etc., are all graded according to their +resistance in ohms. The measurement of resistance in any electrical +instrument or circuit is usually accomplished by comparing its +resistance with that of some known circuit, such as a coil of wire which +has been previously tested. + +The simplest method of measuring resistance is by means of a device +known as the Wheatstone bridge. This instrument is very simple but at +the same time is remarkably sensitive if properly made. A Wheatstone +bridge is shown in Figure 116. + +The base is a piece of well-seasoned hard wood, thirty inches long, six +inches wide, and three-quarters of an inch thick. + +Secure a long strip of No. 18 B. & S. gauge sheet-copper, one inch wide, +and cut it into three pieces, making two of the pieces three inches +long, and the other piece twenty-three and one-half inches long. + +Mount the copper strips on the base, as shown, being very careful to +make the distance between the inside edges of the end-pieces just +twenty-five inches. The strips should be fastened to the base with small +round-headed brass screws. Mount two binding-posts on each of the short +strips in the positions shown in the illustration, and three on the long +strip. These binding-posts should pass through the base and make firm +contact with the strips. + +[Illustration: Fig. 116.—Wheatstone Bridge.] + +Then make a paper scale twenty-five inches long, and divide it into one +hundred equal divisions one-quarter of an inch long. Mark every fifth +division with a slightly longer line, and every tenth division with a +double-length line. + +Start at one end and number every ten divisions, then start at the other +end and number them back, so that the scale reads 0, 10, 20, 30, 40, 50, +60, 70, 80, 90, 100, from right to left at the top and 0, 10, 20, 30, +40, 50, 60, 70, 80, 90, 100, from left to right at the bottom. + +Solder a piece of No. 30 B. & S. gauge German-silver wire to one of the +short copper strips opposite the end of the scale, and then stretch it +tightly across the scale and solder it to the strip at the other end. + +Make a knife-contact by flattening a piece of heavy copper wire as shown +in Figure 117. Solder a piece of flexible wire, such as "lamp cord," at +the other end. It is well to fit the contact with a small wooden handle, +made by boring out a piece of dowel. + +The instrument is now practically complete. + +[Illustration: Fig. 117.—Knife-Contact.] + +In order to use the Wheatstone bridge, it is necessary to have a set of +resistances of known value. The resistance of any unknown circuit or +piece of apparatus is found by comparing it with one of the known coils. +It is just like going to a store and buying a pound of sugar. The grocer +weighs out the sugar by balancing it on the scales with an iron weight +of known value, and taking it for granted that the weight is correct, we +would say that we have one, five, or ten pounds of sugar, as the case +may be. + +The Wheatstone bridge might be called a pair of "electrical scales" for +weighing resistance by comparing an unknown coil with one which we know +has a certain value. + +The next step is to make up some standard resistance coils. Secure some +No. 32 B. & S. gauge single-cotton-covered wire from an electrical +dealer and cut into the following lengths, laying it straight on the +floor but using care not to pull or stretch it. + +1/2 ohm coil—3 feet 1/2 inch +1 ohm coil—6 feet 1 1/4 inches +2 ohm coil—12 feet 2 1/2 inches +5 ohm coil—30 feet 6 1/4 inches +10 ohm coil—61 feet +20 ohm coil—122 feet +30 ohm coil—183 feet +50 ohm coil—305 feet + +These lengths of wire are then wrapped on the spools in the following +manner. + +[Illustration: Fig. 118.—Resistance-Coil. _A_ shows how the Wire is +doubled and wound on the Spool. _B_ is the completed Coil.] + +This method of winding is known as the non-inductive method, because the +windings do not generate a magnetic field, which might affect the +galvanometer needle used in connection with the Wheatstone bridge as +described later on. + +Each length of wire should be doubled exactly in the middle, then +wrapped on the spools like a single wire, the two ends being left free +for soldering to the terminals as shown in Figure 118, B. + +The spools may be the ordinary reels upon which cotton and sewing-silk +are wrapped. + +The terminals of the spools are pieces of stout copper wire, No. 12 or +No. 14 B. & S. gauge. Two pieces of wire about three inches long are +driven into holes bored in the ends of each spool. A small drop of +solder is used permanently to secure the ends of the coil to each of the +heavy wire terminals. + +The spools are then dipped into a pan of molten paraffin and boiled +until the air bubbles cease to rise. + +The spools should be marked 1, 2, 10, 20, 30, and 50, according to the +amount of wire each one contains as indicated in the table above. + + +How to Use a Wheatstone Bridge for Measuring Resistance + + +The instrument is connected as in Figure 116. + +The unknown resistance or device to be measured is connected across the +gap at _B_. One of the standard known coils is connected across the gap +at _A_. A sensitive galvanometer or a telephone receiver and two cells +of battery are also connected as shown. + +If a telephone receiver is used, place it to the ear. If a galvanometer +is used instead, watch the needle carefully. Then move the sharp edge of +the knife-contact over the scale along the German-silver "slide wire" +until a point is reached when there is no deflection of the needle or no +sound in the telephone receiver. + +If this point lies very far on one side or the other of the center +division on the scale, substitute the next higher or lower known +resistance spool until the point falls as near as possible to the center +of the scale. + +When this point is found, note the reading on the scale carefully. Now +comes the hardest part. Almost all my readers have no doubt progressed +far enough in arithmetic to be able to carry on the following simple +calculation in proportion which must be made in order to find out the +resistance of the unknown coil. + +The unknown resistance, connected to _B_, bears the same ratio to the +known coil, at _A_, that the number of divisions between the +knife-contact and the right-hand end of the scale (lower row of figures) +bears to the number of divisions between the knife-edge and the +left-hand end of the scale (upper row of figures). + +We will suppose that a 5-ohm coil was used at _A_ in a test, and the +needle of the galvanometer stopped swinging when the knife-contact +rested on the 60th division from the left-hand end, or on the 40th from +the right. Then, in order to find the value of the unknown resistance at +_B_, it is simply necessary to multiply the standard resistance at _A_ +by the number of left-hand divisions and divide the product by the +number of right-hand divisions. The answer will be the resistance of _B_ +in ohms. + +The calculation in this case would be as follows: + +5 X 40 = 200 + +200/60 = 3.33 ohms + +3.33 ohms is the resistance of _B_. + +This explanation may seem very long and complex, but if you will study +it carefully you will find it to be very simple. When once you master +it, you will be enabled to make many measurements of resistance which +will add greatly to the interest and value of your experiments. + + + +CHAPTER IX BELLS, ALARMS, AND ANNUNCIATORS + + +An electric bell may be bought almost anywhere for twenty-five cents, +and from the standpoint of economy it does not pay to build one. + +A bell is not a hard thing to construct, and the time and money spent +will be amply repaid by the more intimate knowledge of this useful piece +of apparatus which will be gained by constructing it. + +The base is four inches wide and five and one-half inches long. + +The magnets consist of two machine bolts, wound with No. 22 +cotton-covered magnet wire. Fiber ends are fitted on the bolts to hold +the wire in place. + +The wire is wound on each of the magnets separately. Cover the cores +with two or three layers of paper before winding on the wire. The ends +of the wire are led through holes in the core ends. The ends of the +bolts are passed through the yoke, and the nuts applied to hold them in +place. + +The magnets are clamped down to the bell-base by means of a hard-wood +strip having a screw passed through it between the magnets into the +base. + +[Illustration: Fig. 119.—Details of the Magnet Spools, and Yoke for an +Electric Bell.] + +The armature of the bell is shown in Figure 120. It is made of a piece +of iron having a steel spring riveted to it, as illustrated. The +armature is fastened to a small block mounted on the lower left-hand +corner of the base. + +[Illustration: Fig. 120.—Details of the Armature, and Contact Screw.] + +A second block with a contact-point made from an ordinary brass screw by +filing the end into the shape shown in the illustration, is mounted on +the base so that it is opposite the end of the contact-spring fastened +to the armature. The gong may be secured from an old bell or alarm +clock. It is mounted on the upper part of the base in such a position +that the hammer will strike it on its lower edge. + +The instrument is connected as shown in Figure 121. One terminal of the +magnets is connected to the contact-screw. The other end is connected to +the binding-post. A second binding-post is connected to the armature. + +[Illustration: Fig. 121.—The Completed Bell.] + +The armature spring should be bent so that the armature is pushed over +against the contact. + +If a battery is connected to the bell, the electromagnets will pull the +armature and cause the hammer to strike the gong. As soon as the +armature has moved a short distance, the spring will move away from the +contact and break the circuit. The magnets cease pulling as soon as the +current is cut off and the armature spring then causes the armature to +move back and touch the contact. As soon as the contact is made, the +armature is drawn in again and the process is repeated. + +[Illustration: Fig. 122.—Diagram showing how to connect a Bell, Battery, +and Push-Button.] + +A little experimenting with the bell will soon enable one to find its +best adjustment. Figure 122 shows how to connect a bell to a battery and +a push-button. A push-button is simply a small switch which closes the +circuit when pressed. Do not make the armature spring too weak, or the +hammer will move very slowly and with very little life. Each time that +the armature moves toward the magnets, it should barely touch the iron +cores before the ball strikes the bell. + +After you get the bell in good working order, it is well to make a small +box to serve as a cover for the working parts of the instrument, leaving +only the gong exposed. + +[Illustration: Fig. 123.—Two Simple Push-Buttons.] + +[Illustration: Fig. 124.—Diagram showing how to arrange a Bell System of +Return Signals.] + +It is sometimes desirable to arrange two bells and two push-buttons, so +that a return signal can be sent. In that case the circuit shown in +Figure 124 may be employed. It is then possible for the person answering +the bell to indicate that he has heard the call by pushing the second +button. For instance, one push-button and bell might be located on the +top floor of a house and the other bell and button in the basement. A +person in the basement wishing to call another on the top floor would +push the button. The person answering could return the signal by pushing +the button on the top floor and cause the bell in the basement to ring. + + +A Burglar Alarm + + +A simple method of making an efficient burglar alarm is shown in Figure +125. The base is a piece of wood about five by six inches, and half an +inch thick. A small brass strip, _A_, is fastened to the base by means +of two round-headed wood screws and the ends turned up at right angles. +The lever, _B_, is also a strip of brass. One end is bent out, so as to +clear the strip and the screws that are under it. The lever is pivoted +in the middle with a screw and a washer. A small hole, _D_, is bored in +the lower end through which a spring and a string are passed. The other +end of the spring is fastened under a screw and washer, _C_. + +[Illustration: Fig. 125.—Burglar-Alarm Trap.] + +In order to set the alarm, first fasten the base in any convenient +place. Carry the string across the room and fasten it. Adjust the string +so that the lever is half-way between the two ends of the strip, _A_. + +If the string is disturbed, it will pull the lever over against the +strip, _A_. If the string is cut, the spring will pull the lever over to +the opposite side. In either case, if the alarm is properly connected to +a bell and battery, the circuit will be closed if the string is +disturbed, and the bell will ring. + +One wire leading from the bell and the battery should be connected to +_A_, and the other to the screw and washer, _C_. + +The alarm may be arranged across a window or doorway and a black thread +substituted for the string. Any one entering in the dark and unaware of +the existence of the alarm is liable to break the thread and ring the +bell. + + +An Electric Alarm + + +It is often desirable to arrange an electrical alarm clock so that a +bell will ring continuously until shut off. + +[Illustration: Fig. 126.—An Early-Riser’s Electric Alarm Attachment for +a Clock.] + +Figure 126 shows an electrical alarm attachment. It consists of a wooden +box, large enough to receive an ordinary dry cell. A bell is fastened on +the outside of the box. Connect one terminal of the battery to one +terminal of the bell. Connect the other bell and battery terminals, each +to a short piece of brass chain, about four inches long. The ends of the +chain are then fastened to a small piece of sheet fiber or hard rubber, +so that they are insulated from each other. The opposite end of the +fiber is fastened to a piece of wire spring having a garter or suspender +clip soldered to the end. + +[Illustration: Fig. 127.—Details of the Chain Electrodes, etc.] + +The operation of this electrical attachment is very simple. Wind up the +alarm key of an ordinary alarm clock and place the clip on the key. +Place the clock in such a position that the two chains do not touch each +other. Set the clock. When the mechanical alarm goes off, the key will +revolve and twist the two chains, thus closing the electric circuit and +causing the bell to ring. The bell will ring until the clamp is removed. +The outfit can be attached to any ordinary alarm clock. + + +An Annunciator + + +Annunciators are often placed in bell and burglar alarm-circuits to +indicate where the button ringing the bell was pushed, in case there are +several. + +The separate indicators used on an annunciator are called _drops_. + +[Illustration: Fig. 128.—An Annunciator Drop.] + +A drop may be made from an electromagnet and some brass strips, etc. + +The frame is cut from heavy sheet-brass and shaped as shown in Figures +128 and 129. + +The drop bar is a strip of metal which is pivoted on the frame at its +lower end and has the upper end turned up to receive a numeral or +letter. + +The armature is made from a strip of sheet-iron. It is pivoted on the +frame at its upper end. The strip is bent at right angles so as to fall +in front of the magnet. The lower part of the armature is bent into a +hook. The hook fits into a slot cut in the drop bar. A fine wire spring +is placed between the frame and the upper end of the armature so as to +pull the armature away from the core when the current is not passing +through the magnet. + +The electromagnet should be wound with No. 25 B. & S. cotton-covered +magnet wire. + +When a current is sent through the magnet, it will draw the armature in. +This action releases the hook from the edge of the slot in the drop bar +and permits the bar to drop and bring the number or letter down into +view. + +[Illustration: Fig 129.—Details of the Drop-Frame and Armature.] + +A number of "drops" may be arranged on a board and placed in different +circuits so as to indicate which circuit is closed at any time. It is a +good plan to arrange a bar to act as a stop, so that the numeral will +not drop down too far. Each time that any one of the drops falls, it +must be reset by pushing the bar back into position. + + + +CHAPTER X ELECTRIC TELEGRAPHS + + +Experiments in telegraphy were carried out as far back as the year 1753, +when it was proposed to transmit messages by representing the letters of +the alphabet by combinations of sparks produced by a static machine; but +these were of little practical value and nothing of any importance was +accomplished until after the discovery of galvanic current. + +Many of these old experiments were very crude and appear somewhat +ridiculous when compared with the methods of nowadays. The earliest +proposal for an electric telegraph appeared in the _Scots’ Magazine_ for +February, 1753, and shows several kinds of proposed telegraphs acting by +the attractive power of electricity, conveyed by a series of parallel +wires, one wire corresponding to each letter of the alphabet and +supported by glass rods at every twenty yards. Words were to be spelled +by the action of the electricity in attracting paper letters, or by +striking bells corresponding to letters. + +The modern telegraph consists essentially of four things, namely: + +A battery which produces an electric current. + +A wire which conducts the electric current from one point to another. + +A transmitter for shutting the current off and on. + +An electro-magnetic receiving apparatus, which gives out in sounds, the +signals made by the pulsations of the current from a distant point. + +The battery may be almost any form of battery. Gravity cells are +preferred, however, for telegraph work. + +Heavy galvanized iron wire is usually employed as the "line." It is +necessary to use non-conductors wherever the wire is fastened. Glass +insulators placed on a wooden pin or bracket, which is fastened to the +pole or building on which the wire is to be supported, are used for +outside work. Inside of buildings, rubber tubes are used where the wires +pass through walls, etc. + +The operation of a telegraph is not, as many people suppose, a +complicated or difficult matter to understand, but is quite simple. + +The key is a contrivance for controlling the passage of the electric +current in much the same manner as an ordinary switch. It consists of a +steel lever, swung on trunnion-screws mounted in a frame, and provided +with a rubber knob which the operator grasps lightly with the thumb and +forefinger. On pressing the lever downward, a platinum point fastened on +the under side of the lever is brought into contact with another point +set into a rubber bushing in the base of the key, so that there is no +electrical connection between the two points unless the key is pressed +down or "closed," as it is often termed. The key is usually fastened to +the operating bench by two rods called "legs." The lever is provided +with screws which permit the stroke of the key to be very closely +adjusted. + +[Illustration: Fig. 130.—A Typical Telegraph Key, showing the Various +Parts.] + +The line wire and battery are connected to the key, so that no current +can flow until the key is pressed and the contacts brought together. + +A "sounder" consists of two electromagnets mounted on a base under a +movable flat piece of iron which is attracted by the magnetism of the +electromagnets when a current flows through them and is withdrawn by a +spring when no magnetism excites the windings. + +This piece of iron, which is called the armature, is mounted upon a +strip of brass or aluminum called the lever. The lever strikes against a +brass "anvil" and produces the "clicks," which form the dots and dashes +of the telegraph alphabet. + +[Illustration: Fig. 131.—A Typical Telegraph Sounder, showing the +Various Parts.] + +Every time that the key is pressed, an electric current is sent out into +the line. The current flows through the magnets of the sounder and +causes the armature to be drawn downward. The lever strikes the anvil +and produces a "click." When the key lever is released, the current is +shut up and the lever flies up and clicks against the top of the anvil. + +The period of time between the first click and the second click may be +varied at will according to the length of time that the key is held +down. A short period is called a _dot_ and a long period a _dash_. +Combinations of dots, dashes, and spaces arranged according to the Morse +Alphabet, make intelligible signals. + + +How To Make a Simple Key and Sounder + + +The little telegraph instruments shown in Figures 132 and 133 are not +practical for long lines but may be used for ticking messages from one +room to another, and can be made the source of much instruction and +pleasure. + +[Illustration: Fig. 132.—A Simple Home-made Telegraph Key.] + +The key is a strip of brass fastened to a wooden base in the manner +shown in Figure 132. It is fitted with a knob of some sort on the front +end, so that it is conveniently gripped with the fingers. + +The little bridge is made from heavy sheet-brass and prevents the lever +from moving too far away from the contact on the upward stroke. + +Connections are made to the key lever at the back end and the contact in +front by the binding-posts, _A_ and _B_. The post, _C_, connects with +the bridge. + +The sounder consists of two small electromagnets mounted in a vertical +position on a wooden base. The magnets are connected at the bottom by a +strip of heavy sheet-iron which acts as a yoke. + +[Illustration: Fig. 133.—A Simple Home-made Telegraph Sounder.] + +The armature is made out of sheet-iron, rolled up in the manner shown in +the illustration. One end of the armature is fastened to a wooden block +in such a position that the armature comes directly over the magnets and +about one-eighth of an inch above them. The opposite end of the armature +moves up and down for about an eighth of an inch between two screws, +each fastened in a wooden block mounted on an upright board in the back +of the magnets. The purpose of the screws is to make the "click" of the +sounder louder and clearer than it would be if the armature only struck +the wood. + +A rubber band or a small wire spring passing over a screw and connected +at the other end to the armature will draw the latter away from the +magnets when the current is not passing. + +The terminals of the magnets are connected to binding-posts mounted on +the base. + +[Illustration: Fig. 134.—A Diagram showing how to connect two Simple +Telegraph Stations.] + +The key and sounder should be placed in series with one or two cells of +a battery. Pressing the key will then cause the armature of the sounder +to be drawn down and make a click. When the key is released, the +armature will be drawn up by the spring or rubber band and make a second +click. + +Hardly a boy interested in mechanics and electricity has not at some +time or other wished for a telegraph instrument with which to put up a +"line" with his chum. + +A practical working set of such instruments can be very easily +constructed, and with little expense, by following the sketches and +instructions given here. + +The magnets for the sounder may either be constructed by the intending +telegraph operator or secured from some old electrical instrument such +as a magneto-bell. In the latter case, the hardest part of the work will +be avoided. + +If they are to be home-made, the following suggestions may prove of +value in carrying out their construction. + +[Illustration: Fig. 135.—A Complete Telegraph Set, consisting of a +Keyboard and a Sounder.] + +The cores are made from one-quarter-inch stove-bolts with the heads cut +off. The magnet heads are cut out of hard-wood fiber, one-eighth of an +inch thick and one inch in diameter. They should fit tightly and be held +in place with glue. They are separated so as to form a winding space +between of seven-eighths of an inch. The magnets should be wound full of +No. 25 B. & S. gauge cotton-covered wire. + +[Illustration: Fig. 136.—Details of the Telegraph Set shown in Figure +135.] + +The yoke is made of enough strips of sheet-iron, one-half inch wide and +two inches long, to form a pile one-quarter of an inch thick. Two +one-quarter-inch holes are bored in the opposite ends of the yoke, one +and one-half inches apart. The lower ends of the magnet cores are passed +through these holes. The ends should project one-half of an inch beyond +the yoke. + +They are passed through two holes in a base-board three-quarters of an +inch thick. The holes are countersunk from the lower side, so that a nut +can be screwed on the lower end of each and the magnets held tightly in +an upright position. The remaining parts of the instrument are very +easily made, and are so clearly shown by the drawing that it is hardly +necessary to say more than a few words in explanation. + +The lever or tongue, the anvil, the standard, and the lever of the key +are all cut out of hard-wood according to the pattern shown in the +illustration. + +The armature is a piece of soft iron fastened to the lever with a small +brass screw. + +Tacks are placed under the heads of the adjusting screws on the sounder +so that it will click more loudly. + +The rubber band acts as a spring to counteract the weight of the +armature and lever and draw it up as soon as the current is cut off. The +movement of the lever should be so adjusted that it is only sufficient +to make an audible click. + +Use care to avoid friction between the lever and the standard, so that +the former will move with perfect freedom. + +All the screws used in the work should be round-headed brass wood screws +with the points filed flat. Bore a small hole before screwing them into +place so as to avoid splitting the wood. + +The construction of the key is even more simple than that of the +sounder. It should move up and down without any side motion. + +The circuit-closer should be kept closed when the instruments are not in +use, and when you are receiving a message. As soon as you are through +receiving and wish to transmit, you should open your circuit-closer and +your friend close his. + +The tension of the spring under the lever of the key must be adjusted to +suit the needs of each individual operator. + +[Illustration: Fig. 137.—A Diagram showing how to connect two Complete +Telegraph Sets, using one Line Wire and a Ground. The Two-Point Switches +throw the Batteries out of Circuit when the Line is not in use.] + +The diagram for connecting the instruments is self-explanatory. In +cities or towns where a "ground" is available by connecting to the gas +or water pipes, one line wire may be easily dispensed with. Or, if +desirable, a ground may be formed by burying a large plate of zinc +(three or four feet square) in a moist spot and leading the wire to it. + + +How To Build a Telegraph Relay + + +In working a telegraph over a long line or where there are a large +number of instruments on one circuit, the currents are often not strong +enough to work the sounder directly. In such a case a _relay_ is used. +The relay is built on the same principle as a sounder, but the parts are +made much lighter, so that the instrument is more sensitive. The +armature of a relay is so small and its movement so little that its +clicking is scarcely audible. It is therefore fitted with a second set +of contacts and connected to a battery and a sounder, which is to set in +operation every time the contacts close. The principle of a relay is +that a weak current of insufficient strength to do the work itself may +set a strong local current to do its work for it. + +There are many forms of relays, and while that which is described below +is not of the type commonly used on telegraph lines, it has the +advantage of being far more sensitive than any instrument of the regular +line relay type that the average experimenter could build. + +[Illustration: Fig. 138.—Details of the Relay Parts.] + +Make the magnets from one-quarter-inch stove-bolts, and cut them off so +that they will form a core about two and one-quarter inches long. Fit +each of the cores with two fiber heads to hold the wire in place. +Insulate the legs with paper and wind each with about fifty layers of +No. 30 B. & S. gauge single-cotton-covered magnet wire. The winding +space between the magnet’s heads should be one and one-eighth inches. + +The upper ends of the magnet cores should be allowed to project about +one-quarter of an inch beyond the fiber head. The end of the core is +filed flat, as shown in the illustration. + +The magnets are mounted upon an iron yoke, three-sixteenths of an inch +thick. The holes in the yoke should be spaced so that there is a +distance of one and one-half inches between the centers of the magnet +cores. + +The armature of the relay is mounted on a small steel shaft with sharp +points at each end. The exact shape of the armature may be best +understood from the illustrations. + +The lower end of the shaft rests in a small cone-shaped depression made +by driving a center punch into the yoke half-way between the two +magnets. + +The top bearing is a strip of brass projecting from a wooden support. +The end of the shaft rests in a depression similar to that in the yoke. + +The contact lever is made of brass and forced on the shaft below the +armature. It swings between a small brass clip fastened to one side of +the support and a little screw held in a similar clip on the opposite +side. + +The contact clip is made of spring brass about No. 22 gauge in +thickness. It may be adjusted by a screw passing through the support. + +The armature may be controlled in its movement so that the latter will +be very slight by adjusting the screws. + +There should not be any friction in the bearings and the armature should +move with perfect freedom. The armature should approach the ends of the +magnet cores until a space about the thickness of heavy paper separates +them and should not touch them. + +[Illustration: Fig. 139.—The Completed Relay.] + +The spring is made of fine brass wire. It is fastened to the armature +shaft, and the screw mounted on the wooden support with a piece of silk +thread. The thread is passed around the shaft once or twice so that the +tension of the spring will cause the armature to move away from the pole +pieces just as soon as the current flowing through the magnets ceases. + +[Illustration: Fig. 140.—A Diagram showing how to connect a Relay, +Sounder, and Key. Closing the Key will operate the Relay. The Relay will +then operate the Sounder in turn.] + +The tension of the spring may be adjusted by turning the screw with a +screw-driver. If the armature tends to stick to the magnet poles fasten +a small piece of paper to the poles with some shellac. + +The terminals of the magnets are connected to two binding-posts marked +_A_ and _B_. The binding-posts marked _C_ and _D_ are connected +respectively to the contact clip and the brass bearing on the top of the +wooden support. + +The diagram in Figure 140 shows how the relay is connected to a +telegraph line. + + +How To Learn To Telegraph + + +The instruments so far described have been practical working telegraph +instruments, but they lack the fine points of commercial apparatus and +it is not possible to become as efficient an operator with their aid as +with a real key and sounder. + +If the young experimenter desires to become a proficient telegraph +operator, the first thing to do is to purchase a Learner’s telegraph key +and sounder. + +Connect a dry cell to the binding-posts on the back of the instrument. +Screw the set down on a table about eighteen inches from the front edge, +so that there is plenty of room for the arm to rest. See that none of +the various adjustment screws about the instrument are loose and that +the armature of the sounder moves freely up and down through a distance +of about one-sixteenth of an inch. + +The spring which draws the lever upwards away from the magnets should be +set only at sufficient tension to raise the lever when no current is +passing. If too tight, the spring will not allow the armature to respond +to the current flowing through the magnets. + +The key is provided with several adjustment-screws to regulate the +tension and the play of the lever to suit the hand of the operator. A +little practice will enable the student to judge best for himself just +how the key should be set. + +The next step is to memorize the alphabet, so that each character can +instantly be called to mind at will. The punctuation marks are not used +very frequently, and the period is the only one which the student need +learn at first. + +The Morse alphabet consists of dots, dashes, and spaces. Combinations of +these signals spell letters and words. + +Many of the characters are the reverse of others. For example, _A_ is +the reverse of _N_. _B_ and _F_, _D_ and _U_, _C_ and _R_, _Q_ and _X_, +_Z_ and _&_, are the other reverse letters, so if the formation of one +of each of these letters is memorized the reverse is easily mastered. + +It is important that the beginner should learn how properly to grasp the +key, for habits are easily formed and a poor position will limit the +sending speed of the operator. + +Place the first or index finger on the top of the key-handle, with the +thumb under the edge; and the second finger on the opposite side. The +fingers should be curved so as to form a quarter-section of a circle. +Bring the third and fourth fingers down so that they are almost closed +on the palm of the hand. Rest the arm on the table in front of the key +and allow the wrist to be perfectly limber. + +[Illustration: Fig. 141.—How to hold a Telegraph Key.] + +The grasp on the key should be firm but not rigid. Avoid using too much +strength or a light hesitating touch. Endeavor to acquire a positive, +firm up and down motion of the key. Avoid all side pressure, and do not +allow the fingers to leave the key when making the signals. The movement +is made principally with the wrist, with the fingers and hand perfectly +elastic. + +A dot is made by a single instantaneous, downward stroke of the key. A +dash is made by holding the key down for the same period of time that it +takes to make three dots. A long dash is made by holding the key down +for the same time that it takes to make five dots. + +A space in the letters, such as, for instance, the space between the +first and last two dots in the letter _R_ should occupy the time of one +dot. The space between each letter should occupy the time required for +two dots, and the space between words should occupy the time required +for three dots. + +Commence the use of the key by making dots in succession, first at the +rate of two every second, and increasing the speed until ten can be +made. Practice should be continued until three hundred and sixty dots a +minute can be made with perfect regularity. + +Then begin making dashes at the rate of two every three seconds, and +continue until one hundred and twenty a minute can be made with perfect +regularity. + +Practise the long dashes at the rate of one a second, and increase until +ninety can be made in a minute. + +[Illustration: Fig. 142.—The Morse Telegraphic Code.] + +When this has been accomplished, practise the following letters until +they can be perfectly made. Each row of letters is an exercise which +should be practised separately until mastered. + +Dot Letters + + E I S H P 6 + +Dot and Space Letters + + O C R Y Z & + +Dash Letters + + T L M 5 O + +Dots and Dashes + + A U V 4 + +Dashes and Dots + + N D B 8 + +Mixed Dots and Dashes + + F G J K Q W X 1 2 3 7 9 Period + +After you can write these different letters, practise making words. +Select a list of commonly used words. When words seem easy to write, +practise sending pages from a book. + +Systematic and continual practice will enable the student to make +surprising progress in mastering the art of sending. + +Reading and receiving messages must be practised with a companion +student. Place two instruments in separate rooms or in separate houses +so that the operators will be entirely dependent upon the instruments +for their communication with each other. Start by transmitting and +receiving simple messages. Then use pages from a book, and increase the +speed until it is possible to send and receive at least 15 words a +minute without watching the sounder but merely depending upon the clicks +to determine the duration of the dots and dashes. + +Figure 140 shows how to arrange a regular telegraph line for two +stations. Gravity batteries should be used for regular telegraph work. +It is necessary that the key should be kept closed by having its +circuit-closer shut when messages are not being sent. If one of the keys +is left open the circuit is broken, and it is not possible for a person +at the other end of the line to send a message. + +Every telegraph office has a name or call usually consisting of two +letters; thus for New York the call might be N. Y. and for Chicago, C. +H. + +If New York should desire to call Chicago, he would repeat the call +letters, C H., until answered. Chicago would answer by sending I, +several times and signing, C H. When so answered, New York would proceed +with the message. + + + +CHAPTER XI MICROPHONES AND TELEPHONES + + +In 1878, David Edward Hughes discovered that the imperfect contact +formed between two pieces of some such substance as carbon or charcoal +is very sensitive to the slightest changes in pressure, and when +included in an electric circuit with a battery and a telephone receiver, +will transmit sounds. Such an instrument is called a _microphone_. It +has various forms but in most of them one piece of carbon or charcoal is +held loosely between two other pieces in such a manner as to be easily +affected by the slightest vibrations conveyed to it through the air or +any other medium. + +[Illustration: Fig. 143.—A Microphone connected to a Telephone Receiver, +and a Battery.] + +Figure 143 illustrates a simple form of instrument embodying this +principle. A small pencil of carbon is supported loosely between two +blocks of the same substance glued to a thin wooden sounding-board of +pine. The sounding-board is mounted in an upright position on a wooden +base. The carbon pencil rests loosely in two small indentations in the +carbon blocks. The blocks are connected, by means of a very fine wire or +a strip of tinfoil, with one or two cells of battery and a telephone +receiver. Any vibration or sounds in range of the microphone will cause +the sounding-board to vibrate. This will affect the pressure of the +contact between the carbon pencil and the two blocks. When the pressure +between the two is increased the resistance in the path of the electric +current is decreased and more current immediately flows through the +circuit. On the other hand, when the pressure is decreased, the +resistance is increased and less current flows through the telephone +receiver. The amount of current flowing in the circuit thus keeps step +with the changes in the resistance, and accordingly produces sounds in +the telephone receiver. The vibrations emitted from the receiver are +usually much greater than those of the original sounds, and so the +microphone may be used to magnify weak sounds such as the ticking of +clock-wheels or the footfalls of insects. If a watch is laid on the base +of the microphone, the ticking of the escapement wheel can be heard with +startling loudness. The sounds caused by a fly walking on a microphone +may be made to sound as loud as the tramp of a horse. + +[Illustration: Fig. 144.—A Very Sensitive Form of Microphone, with which +the Footsteps of a Fly can be heard.] + +The electrical _stethoscopes_ used by physicians to listen to the action +of the heart are in principle only a microphone and telephone receiver +connected to a battery. + +The drawing in Figure 144 illustrates a very sensitive microphone that +is quite easy to make. With this instrument it is possible to hear the +tramping of a fly’s feet or the noise of its wings. + +The base upon which the apparatus is mounted serves as the +sounding-board and is made in the form of a hollow wooden box. It can be +made from an ordinary cigar-box by removing the paper and taking the box +apart. The piece forming the top of the box must be planed down until it +is only three thirty-seconds of an inch thick. The box should measure +about five inches square and three-quarters of an inch thick when +finished. Do not use any nails or small brads whatsoever in its +construction, but fasten it together with glue. If you use any nails you +will decrease the sensitiveness of the instrument quite appreciably. The +bottom of the box should be left open. The result is a sounding-board of +the same principles as that of the banjo head. Small feet, one-quarter +of an inch square, are glued to the four under corners so as to raise +the bottom clear of the table, or whatever the microphone may be placed +upon. The bottom of each one of the small feet is cushioned with a layer +of felt so that no jars will be transmitted to the instrument by any +object upon which it is resting. + +The carbon pencil used on this type of instrument is pivoted in the +center and rests at one end upon a carbon block. + +The carbon block is made about one inch long, one-quarter of an inch +thick, and one-half of an inch wide. A small hole is drilled near each +end to receive a screw which fastens the block to the sounding-board. A +fine wire is led from one of these screws to a binding-post mounted at +the side of the box. Another wire leads from a second binding-post to a +standard which is also fastened to the sounding-board with a small +screw. + +The standard is made from a sheet of thin brass and is bent into the +shape shown in the illustration. + +The pencil is a piece of one-quarter-inch carbon rod, two and +three-quarter inches long. A small hole is drilled one and five-eighths +of an inch from one end with a sewing-needle, and a piece of fine brass +wire, pointed at both ends, pushed in. The wire should be a tight fit in +the hole. It should be about one-half of an inch long, and may be made +from an ordinary pin. + +The slide-bar is used to regulate the pressure of the pencil upon the +carbon block and is simply a piece of soft copper wire about one-eighth +of an inch in diameter. It is bent into the shape shown in the +illustration so that it will slide over the carbon pencil. The sides of +the standard should press just tightly enough against the ends of the +pivot which passes through the carbon pencil to hold it in position +without slipping, and at the same time allow it to swing freely up and +down. + +The two binding-posts should be connected in series with two dry cells +and a pair of good telephone receivers. Place the receivers against the +ears. Move the slide-bar gently back and forth until the voice of any +one talking in another part of the room can be heard distinctly in the +telephone receivers. In order to hear faint whispers, move the slide-bar +away from the carbon block. + +In order to hear a fly walk it is necessary to have the carbons very dry +and clean. The instrument must be very carefully adjusted. Cover the +microphone with a large glass globe and place a fly inside of the globe. +Whenever the fly walks on any part of the microphone you will be able to +hear each footstep in the telephone receivers. When he flies about +inside of the globe, his wings will cause a loud roaring and buzzing +noise to be heard in the receivers. + + +Telephones + + +Not many years ago, when the telephone made its first appearance, it was +the wonder of the times just as wireless telegraphy is to-day. Starting +as an exceedingly simple and inexpensive apparatus, it has gradually +developed into a wonderful and complex system, so that at the present +time, instead of experiencing difficulty in telephoning over distances +of fifty or one hundred miles, as at first, it is possible to carry on a +conversation over a line two thousand miles long as easily as it is face +to face. + +Like the telegraph, the principle of the telephone is that of a current +of electricity flowing over a line wire into a pair of electro-magnets, +but with many important differences. + +When compared with telegraph apparatus, the telephone is found to be +exceedingly sensitive. A telegraph relay requires perhaps about +one-hundredth of an ampere to work it properly. A telegraph sounder will +require about one-tenth of an ampere, but a telephone receiver will +render speech audible with less than a millionth of an ampere, and +therefore may almost be said to be a hundred thousand times more +sensitive than a sounder. + +Another difference between the telephone and the telegraph lies in the +fact that the currents flowing over a telegraph line do not usually vary +at a rate greater than twenty or thirty times a second, whereas +telephone currents change their intensity hundreds of times a second. + +The telephone is an instrument for the transmission of speech to a +distance by means of electricity, wherein the speaker talks to an +elastic plate of thin sheet-iron which vibrates and sends out a +pulsating current of electricity. + +The transmission of the vibrations depends upon well-known principles of +electricity, and does not consist of the actual transmission of sounds, +but of electrical impulses which keep perfect accord or step with the +sound waves produced by the voice in the transmitter. These electrical +currents pass through a pair of small electro-magnets acting upon a +plate or diaphragm, which in turn agitates the air in a manner similar +to the original voice speaking into the transmitter and thus emits +sounds. + +That part of the apparatus which takes up the sounds and changes them +into electric currents composes the _transmitter_. When words are spoken +into the mouthpiece they strike a diaphragm, on the back of which is +fastened a small cup-shaped piece of carbon. A second cup is mounted in +a rigid position directly back of the first. The space between them is +filled with small polished granules of carbon. When these granules are +in a perfectly loose state and are undisturbed, their resistance to an +electric current is very great and they allow almost none to flow.² When +slightly compressed their resistance is greatly lowered and they permit +the current to pass. The vibrations of the diaphragm cause the carbon +cup mounted on its back to move and exert a varying pressure upon the +granules with a corresponding variation in their resistance and the +amount of current which will pass through. + +[Illustration: Fig. 145.—A Telephone System, consisting of a Receiver, +Transmitter, and a Battery connected in Series. Words spoken into the +Transmitter are reproduced by the Receiver.] + +The _receiver_, or that part of the apparatus which transforms the +pulsating current back into sound waves consists of a thin iron disk, +placed very near but not quite touching the end of a small steel bar, +permanently magnetized, and about which is wound a coil of fine +insulated wire. + +The transmitter and the receiver are connected together in series with a +battery as in Figure 145. When words are spoken into the transmitter the +little carbon granules are immediately thrown into motion, and being +alternately compressed and released cause corresponding changes in the +current flowing through the receiver from the battery. The magnetism of +the receiver changes with each change in the electric current, and thus +by alternately attracting and repelling the diaphragm causes it to +vibrate and emit sounds. Such is the _principle_ of the telephone. The +telephones in actual service to-day are complicated with bells, +magnetos, induction coils, condensers, relays, and various other +apparatus, which fact renders them more efficient. + +The bells and magnetos are for the purpose of calling the central +operator or the person at the other end of the line and drawing +attention to the fact that some one wishes to get into communication +with him. The older styles of telephones used what is known as a +polarized bell and a hand magneto for this purpose. A polarized bell is +a very sensitive piece of apparatus which will operate with very little +current. A magneto is a small hand dynamo which when turned with a crank +will generate a current causing the bell at the other end of the line to +ring. When the telephone receiver is raised off its hook in order to +place it to the ear the bell and magneto are automatically disconnected +from the line and the receiver and the transmitter are connected in +their place. The current necessary to supply the telephone and receiver +is supplied by two or three dry cells placed inside of each telephone. + +The latest types of instruments employ what is known as the central +energy system, wherein the current is supplied by a large storage +battery located at the central office and serving as a current supply to +all the telephones connected to that system. + +It would be impossible to enter into the history of the telephone far +enough to explain the details of some of the various systems in +every-day use in such a book as this because of the immense amount of +material it would be necessary to present. Such a work would occupy a +volume of its own. Additional information may be readily found in any +reference library. However, the "boy electrician" who wishes to make a +telephone for communicating between the house and barn, or with his chum +down the street, will find the necessary information in the following +pages. If this work is carried out carefully and a home-made telephone +system built and installed it will not only prove a very interesting +undertaking but will also serve to dispel all mystery which may surround +this device in the mind of the young experimenter. + + +How to Build a Telephone + + +Telephone receivers are useful for many purposes in electrical work +other than to receive speech. They are used in connection with wireless +instruments, in place of a galvanometer in measuring electrical +circuits, and for testing in various ways. + +Telephone receivers are of two types. One of them is long and +cumbersome, and is very similar to the original Bell telephone receiver. +The other is small and flat, and is called a "watch-case" receiver. A +watch-case receiver is shown in Figure 146. It consists of a U-shaped +permanent magnet so mounted as to exert a polarizing influence upon a +pair of little electro-magnets, before the poles of which is placed an +iron diaphragm. For convenience, these parts are assembled in a small +cylindrical casing, usually of hard rubber. The permanent magnet exerts +a continual pull upon the diaphragm, tending to draw it in. When the +telephone currents pass through the little magnets, they will either +strengthen the permanent magnet and assist it in attracting the +diaphragm, or detract from its strength and allow the diaphragm to +recede, depending upon which direction the current flows. + +[Illustration: Fig. 146.—A Watch-Case Telephone Receiver.] + +Watch-case receivers are usually employed for wireless telegraph work +because they are very light in weight and can easily be attached to a +head-band in order to hold them to the ears and leave the hands free. +Watch-case receivers can be purchased for forty-five to seventy-five +cents at almost any electrical supply house. They are very useful to the +amateur experimenter in many ways. + +A telephone receiver capable of giving fair results on a short telephone +line can be very easily made, but of course will not prove as efficient +as one which is purchased ready-made from a reliable electrical +manufacturer. + +The first practical telephone receiver was invented by Alexander Graham +Bell and was made somewhat along the same lines as that shown in Figure +147. + +Such a receiver may be made from a piece of curtain-pole, three and +three-quarter inches long and about one and one-eighth inches in +diameter. A hole, three-eighths of an inch in diameter, is bored along +the axis throughout its entire length, to receive the permanent magnet. + +The shell of the receiver is a cup-shaped piece of hard wood, two and +one-half inches in diameter and one inch deep. It will have to be turned +on a lathe. Its exact shape and dimensions are best understood from the +dimensions shown in the cross section in Figure 147. The shell is firmly +attached to one end of the piece of curtain-pole by gluing. + +The permanent magnet is a piece of hard steel, three-eighths of an inch +in diameter and four and five-eighths of an inch in length. The steel +will have to be tempered or hardened before it will make a suitable +magnet, and the best way to accomplish this is to have a blacksmith do +it for you by heating the rod and then plunging it into water when just +at the right temperature. + +[Illustration: Fig. 147.—A Simple Form of Telephone Receiver.] + +One end of the bar is fitted with two thick fiber washers about +seven-eighths of an inch in diameter and spaced one-quarter of an inch +apart. The bobbin so formed is wound full of No. 36 B. & S. gauge +single-silk-covered magnet wire. The ends of the wire are passed through +two small holes in the fiber washers and then connected to a pair of +heavier wires. The wires are run through two holes in the curtain-pole, +passing lengthwise from end to end, parallel to the hole bored to +receive the bar magnet. + +This bar magnet is then pushed through the hole until the end of the rod +on which the spool is fixed is just below the level of the edges of the +shell. + +The two wires are connected to binding-posts, _A_ and _B_, mounted on +the end of the receiver. A hook is also provided so that the receiver +may be hung up. + +The diaphragm is a circular piece of thin sheet-iron, two and one-half +inches in diameter. It is placed over the shell, and the bar magnet +adjusted until the end almost touches the diaphragm. The magnet should +fit into the hole very tightly, so that it will have to be driven in +order to be moved back and forth. + +The diaphragm is held in place by a hard-wood cap, two and three-quarter +inches in diameter and having a hole three-quarters of an inch in +diameter in the center. The cap is held to the shell by means of four +small brass screws. + +The receiver is now completed and should give a loud click each time +that a battery is connected or disconnected from the two posts, _A_ and +_B_. + +The original Bell telephone apparatus was made up simply of two +receivers without any battery or transmitter. In such a case the current +is generated by "induction." The receiver is used to speak through as +well as to hear through. This method of telephoning is unsatisfactory +over any appreciable distances. The time utilized in making a +transmitter will be well spent. + +A simple form of transmitter is shown in Figure 148. The wooden back, +_B_, is three and one-half inches square and three-quarters of an inch +thick. The front face of the block is hollowed out in the center as +shown in the cross-section view. + +The face-plate, _A_, is two and one-half inches square and one-half an +inch thick. A hole, seven-eighths of an inch in diameter, is bored +through the center. One side is then hollowed out to a diameter of one +and three-quarter inches, so as to give space for the diaphragm to +vibrate as shown in the cross-sectional drawing. + +The carbon buttons are one inch in diameter and three-sixteenths of an +inch thick. A small hole is bored in the center of each to receive a +brass machine screw. The hole is countersunk, so as to bring the head of +the screw down as close to the surface of the carbon as is possible. +Then, using a sharp knife or a three-cornered file, score the surface of +the carbon until it is covered with criss-cross lines. + +The diaphragm is a piece of thin sheet-iron cut in the form of a circle +two and one-half inches in diameter. A small hole is bored through the +center of this. One of the carbon buttons is fastened to the center of +the diaphragm with a small screw and a nut. + +Cut out a strip of flannel or thin felt, nine-sixteenths of an inch wide +and three and one-half inches long. Around the edge of the carbon button +mounted on the diaphragm, bind this strip with silk thread in such a +manner that the strip forms a cylinder closed at one end with the +button. + +Fill the cylinder with polished carbon telephone transmitter granules to +a depth of about one-eighth of an inch. These granules will have to be +purchased from an electrical supply house. They are finely polished +small carbon balls, much like birdshot in appearance. + +Slip a long machine-screw through the hole in the second carbon button +and clamp it in place with a nut. Then place the carbon button in the +cylinder so that it closes up the end. The space between the two buttons +should be about three-sixteenths of an inch. Bind the flannel or felt +around the button with a piece of silk thread so that it cannot slip out +of place. The arrangement of the parts should now be the same as that +shown by the cross-sectional drawing in the upper right-hand corner of +Figure 148. + +The complete transmitter is assembled as shown in the lower part of +Figure 148. + +A small tin funnel is fitted into the hole in the face-plate, _A_, to +act as a mouthpiece. + +A screw passes through the back, _B_, and connects to the diaphragm. The +screw is marked "_E_" in the illustration. A binding-post is threaded on +the screw so that a wire may be easily connected. The screw passing +through the back carbon button also passes through a hole in the wooden +back, and is clamped firmly in position with a brass nut so that the +button is held very rigidly and cannot move. The front button, being +attached to the diaphragm, is free to move back and forth with each +vibration of the latter. + +[Illustration: Fig. 148.—A Home-made Telephone Transmitter.] + +The carbon granules should fill the space between the buttons +three-quarters full. They should lie loosely together, and not be packed +in. + +When connected to a battery and a telephone receiver the current passes +from the post, _D_, to the back button, through the mass of carbon +granules into the front button and out at the post, _E_. When the voice +is directed into the mouthpiece, the sound waves strike the diaphragm +and cause it to vibrate. The front button attached to it then also +vibrates and constantly changes the pressure on the carbon granules. +Each change in pressure is accompanied by an immediate change in +resistance and consequently the amount of current flowing. + +Figure 149 shows a complete telephone ready for mounting on the wall. It +consists of a receiver, telephone transmitter, bell, hook, and +push-button. The bell is mounted on a flat base-board. The transmitter +is similar to that just described, but is built into the front of a +box-like cabinet. The box is fitted with a push-button at the lower +right-hand corner. A simple method of making a suitable push-button is +shown in the upper left-hand part of the illustration. It consists of +two small brass strips arranged so that pushing a small wooden plug +projecting through the side of the cabinet will bring the two strips +together and make an electrical connection. + +The "hook" consists of a strip of brass, pivoted at one end with a +round-headed brass wood screw and provided with a small spring, so that +when the receiver is taken off of the hook it will fly up and make +contact with a screw, marked _C_ in the illustration. When the receiver +is on the hook, its weight will draw the latter down against the screw, +_D_. The hook is mounted on the base-board of the telephone, and +projects through a slot cut in the side of the cabinet. + +Four binding-posts are mounted on the lower part of the base-board. The +two marked _B_ and _B_ are for the battery. + +[Illustration: Fig. 149.—A Complete Telephone Instrument. Two +Instruments such as this are necessary to form a simple Telephone +System.] + +That marked _L_ is for the "line," and _G_ is for the ground connection +or the return wire. + +[Illustration: Fig. 150.—Diagram of Connection for the Telephone +Instrument shown in Fig. 149.] + +The diagram of the connections is shown in Figure 150. The line-wire +coming from the telephone at the other station enters through the +binding-post marked _L_, and then connects to the hook. The lower +contact on the hook is connected to one terminal of the bell. The other +terminal of the bell leads to the binding-post marked _G_, which is +connected to the ground, or to the second line-wire, where two are used. + +The post, _G_, and one post, _B_, are connected together. The other post +marked _B_ connects to one terminal of the transmitter. The other +terminal of the transmitter is connected to the telephone receiver. The +other post of the telephone receiver leads to the upper contact on the +hook marked _C_. The push-button is connected directly across the +terminals of the transmitter and the receiver so that when the button is +pushed it short-circuits the transmitter and the receiver. When the +receiver is on the hook and the latter is down so that it makes contact +with _D_ any current coming over the line-wire will pass through the +bell and down through the ground or the return-wire to the other +station, thus completing the circuit. If the current is strong enough it +will ring the bed. When the receiver is lifted off the hook, the spring +will cause the hook to rise and make contact with the screw marked _C_. +This will connect the receiver, transmitter, and the battery to the line +so that it is possible to talk. If, however, it is desired to ring the +bell on the instrument at the other end of the line, all that it is +necessary to do is to press the push-button. This will short-circuit the +receiver and the transmitter and ring the bell. The battery current is +flowing over the line all the time when the receiver is up, but the +transmitter and the receiver offer so much resistance to its flow that +not enough current can pass to ring the bell until the resistance is cut +out by short-circuiting them with the push-button. + +The instruments at both ends of the line should be similar. In +connecting them together care should be taken to see that the batteries +at each end of the line are arranged so that they are in series and do +not oppose each other. One side of the line may be a wire, but the +return may be the ground, as already explained in the chapter on +telegraph apparatus. + +A transmitter of the "desk-stand" type may be made according to the +scheme shown in Figure 151. It consists simply of a transmitter mounted +upon an upright, and provided with a base so that it may stand on a desk +or a table. + +[Illustration: Fig. 151.—A Desk-Stand Type of Telephone.] + +It is also fitted with a hook and a push-button, so that it is a +complete telephone instrument with the exception of the bell and the +battery. The battery and the bell may be located in another place and +connected to the desk-stand by means of a flexible wire or "electrical +cord." + +Figure 152 shows what is known as a telephone induction coil. Induction +coils are used in telephone systems whenever it is necessary to work +over a long distance. Such a system is more complicated, and requires +considerable care in making the connections, but is far superior to the +system just described. + +[Illustration: Fig. 152.—A Telephone Induction Coil.] + +An induction coil consists of two fiber or hard-wood heads, about one +inch square and one-quarter of an inch thick, mounted on the ends of an +iron core composed of a bundle of small iron wires about two and +one-half inches long. The core should be about five-sixteenths of an +inch in diameter. + +The core is covered with a layer of paper and then wound with three +layers of No. 22 B. & S. single-cotton-covered wire. These three layers +of wire form the _primary_. The primary is covered with a layer of paper +and then the secondary is wound on. The secondary consists of twelve +layers of No. 36 B. & S. single-silk-covered magnet wire. It is +advisable to place a layer of paper between layers of the secondary +winding, and to give each one a coating of shellac. The two secondary +terminals of the coil are led out through holes in the fiber head and +kept separate from the primary terminals. + +[Illustration: Fig. 153.—Diagram of Connection for a Telephone System +employing an Induction Coil at each Station.] + +The wiring diagram of a telephone system using an induction coil at each +station is shown in Figure 153. The speech sent over a line using an +induction coil system is much clearer and more easily understood than +that on a line not using such a device. + +In building telephone instruments or connecting them up, care and +accuracy will go a long way towards success. Telephony involves some +very delicate and sensitive vibratory mechanical and electrical actions, +and such instruments must be very carefully made. + + ² A transmitter is really a microphone built especially to receive + the sounds of the human voice, and operates on the same principle. + + + +CHAPTER XII INDUCTION COILS + + +A Medical Coil or shocking coil, as it is properly termed, is nothing +more or less than a small induction coil, and consists of a core, a +primary winding, a secondary winding, and an interrupter. The principle +of an induction coil and that of magnetic induction have already been +explained in Chapter V. It might be well for the readers to turn back to +pages 89-91 and reread them. + +The human body possesses considerable resistance, and the voltage of one +or two ordinary cells of battery is not sufficient to overcome that +resistance and pass enough current through the body to be felt, unless +under exceptional conditions. + +The simplest means employable for raising the voltage of a battery high +enough to produce a shock is the medical coil. + +The first step in making such a coil is to roll up a paper tube, +five-sixteenths of an inch in diameter inside, and two and one-half +inches long. The outer end of the paper is carefully glued, so that it +will not unroll. The tube is filled with pieces of iron wire two and +one-half inches long which have been straightened by rolling between two +boards. The size of the iron wire may vary from No. 20 to No. 24 B. & S. +gauge. Enough should be slipped into the tube to pack it tightly and +admit no more. + +A square block, 1 x 1 x 5-16 inches, is cut out of fiber or a +close-grained hard wood and a hole three-eighths of an inch in diameter +bored through the center. One end of the tube containing the core is +smeared with glue and slipped into the block. The end of the tube is +allowed to project through about one-sixteenth of an inch. A second +block, in the form of a circle three-quarters of an inch in diameter, +one-quarter of an inch thick, and having a three-eighths of an inch hole +through the center, is glued on the opposite end. + +[Illustration: Fig. 154.—Details of Various Parts of a Medical Coil.] + +After the glue has dried, four small holes are drilled in the square +head in the approximate positions shown by Figure 154. Four layers of +No. 22 B. & S. gauge magnet wire (it may be either silk or cotton, +double or single covered) is wound smoothly and carefully over the core. +The terminals are led out of the holes _a_ and _b_. The primary is +covered with two or three layers of paper, and then enough secondary +wound on to bring the total diameter of the coil to about +eleven-sixteenths of an inch. The secondary wire must be much finer than +the primary. It is possible to use any size from No. 32 to No. 36 B. & +S. gauge and obtain good results. The insulation may be either single +silk or single cotton. + +[Illustration: Fig. 155.—Details of Interrupter for Medical Coil.] + +The secondary terminals are led out through the holes _c_ and _d_. It is +perhaps a wise plan to re-enforce these leads with a heavier piece of +wire, because otherwise they are easily broken. + +The interrupter is a simple arrangement capable of being made in several +different ways. The drawing shows an arrangement which can be improved +upon by any experimenters who are familiar with a medical coil. I have +shown the simplest arrangement, so that all my readers will be able to +build it, and those who want to improve it can do so. + +If a small piece of silver is soldered to the spring and to the +contact-point it will give better results. The silver is easily secured +by cutting up a ten-cent piece. One terminal of the primary is connected +to the interrupter spring and the other to a binding-post. The +contact-post is also connected to a binding-post. If a battery is +connected to the two binding-posts, the current will flow from one post +through the coil to the interrupter spring, through the spring to the +contact post, and thence back to the battery, making a complete circuit. +As soon as the current flows, however, it produces magnetism which draws +the spring away from the contact and breaks the circuit, cutting off the +magnetic pull. The spring flies back to the contact but is drawn forward +again immediately and repeats the operation continuously at a high rate +of speed. + +[Illustration: Fig. 156.—Completed Medical Coil.] + +The secondary terminals are led out to two binding-posts to which are +connected two electrodes or handles by means of flexible wires. The +electrode may be made of two ordinary flat strips of sheet-metal or a +piece of tubing. In the latter case, the wires may be connected by +wedging them in with a cork. If the handles are grasped while the +battery is connected to the primary posts and the interrupter is in +operation a powerful shock will be felt. The shock may be regulated from +a weak current that can hardly be felt to a very powerful one by +providing the coil with a piece of iron tubing of about seven-eighths of +an inch inner diameter and two inches long which will slip on and oh the +coil. When the tube is all the way on, the shock is very mild, and when +all the way off, the shock is very strong. Of course any intermediate +strength may be secured at stages between the two extremes. + +The current from medical coils is often prescribed by physicians for +rheumatism and nervous disorders, but must be properly applied. The coil +just described is harmless. It will give a strong shock, but the only +result is to make the person receiving it drop the handles and not be +anxious to try it again. + + +Spark-Coils + + +A "spark-coil" is one of the most interesting pieces of apparatus an +experimenter can possess. The experiments that may be performed with its +aid are varied and many. + +The purpose of a "spark-coil" is to generate enormously high voltages +which are able to send sparks across an air space that ordinary currents +of low voltage could not possibly pierce. The spark-coil is the same in +principle as the small induction coils used as medical or shocking +coils, but is made on a larger scale and is provided with a condenser +connected across the terminals of the interrupter. + +[Illustration: Fig. 157.—Diagram showing Essential Parts of Induction +Coil.] + +It consists of a central iron core surrounded by a coil of heavy wire +called the "primary," and by a second outside winding of wire known as +the "secondary." The primary is connected to a few cells of battery in +series with an interrupter. The interrupter makes and breaks the +circuit, i. e., shuts the current on and off repeatedly. + +Every time that the current is "made" or broken, a high voltage is +induced in the secondary. By means of the condenser connected across the +interrupter terminals, the current at "make" is caused to take a +considerable fraction of time to grow, while at "break," the cessation +is instantaneous. The currents induced in the secondary at break are so +powerful that they leap across the space in a brilliant torrent of +sparks. + + +Building a Spark-Coil + + +Perhaps more attempts are made by experimenters to construct a +spark-coil than any other piece of apparatus, and the results are +usually poor. A spark-coil is not hard to construct, but it requires +careful work and patience. It is not a job to be finished in a day, but +time must be liberally expended in its construction. Satisfactory +results are easily obtained by any one of ordinary mechanical ability if +patience and care are used. + +Parts for spark-coils are for sale by many electrical houses, and it is +possible to purchase a set of such machine-made parts for less than the +separate materials usually cost. + +For the benefit of those who might wish to build a larger coil than the +one described in the following text, a table showing the dimensions of +two other sizes will be found. + +[Illustration: Fig. 158.—Empty Paper Tube, and Tube filled with Core +Wire preparatory to winding on the Primary.] + +*The core* is made of very soft iron wire about No. 20 or 22 B. & S. +gauge, cut to exact length. Each piece should be six inches long. Iron +wire may be purchased from electrical supply houses already cut to +various lengths for twenty cents a pound. In view of the amount of labor +required carefully to cut each piece to length and then straighten it +out so that it will form a neat bundle, it is cheaper to purchase the +wire already cut. Such wire has been annealed, i.e., softened by +bringing to a red heat and then cooling slowly. In case the wire is +purchased at a plumbing shop or a hardware store it must be annealed +before it can be used. This is accomplished by tying the wire in a +compact bundle and placing it in a wood fire where it will grow red-hot. +When this stage is reached, cover the wire with ashes and allow the fire +to die away. + +[Illustration: Fig. 159.—Illustrating the Various Steps in winding on +the Primary and fastening the Ends of the Wire.] + +Cut a piece of tough wrapping paper into strips six inches long and +about five inches wide. Wrap it around a stick or metal rod one-half of +an inch in diameter, so as to form a tube six inches long and having a +diameter of one-half of an inch. Glue the inside and outside edges of +the paper so that the tube cannot unroll and then slip it off the stick. + +[Illustration: Fig. 160.—Complete Primary Winding and Core.] + +Fill the tube with the six-inch wires until it is packed tightly and no +more can be slipped in. + +*The primary* consists of two layers of No. 18 B. & S. gauge +cotton-covered wire wound over the core for a distance of five inches. +One-half pound of wire is more than enough for one primary. The wire +must be wound on very smoothly and carefully. In order to fasten the +inside end so that it will not become loose, place a short piece of tape +lengthwise of the core and wind on two or three turns over it. Then +double the end back and complete the winding. After the first layer is +finished, give it a coat of shellac and wind on the second layer. The +end of the wire is wound with a piece of tape and fastened by slipping +through a loop of tape embedded under the last few turns. The +illustrations will explain more clearly just how this is accomplished. +The second layer is then given a coat of shellac and allowed to dry. +After it is dry, wrap about fifteen layers of paper which have been +soaked in paraffin around the primary. This operation should be +performed in a warm place, over a fire or lighted lamp where the +paraffin may be kept soft, so that the paper will go on tightly. + +[Illustration: Fig. 161.—The Primary covered with Insulating Layer of +Paper ready for the Secondary.] + +The coil is now ready to receive the secondary winding. The core and +primary which have been described are suit-able for a secondary giving +sparks from one-half to three-fourths of an inch long. + +*The secondary* winding consists of several thousand turns of very fine +wire wound on in smooth even layers with paper between each two layers. + +The following table shows the size and amount of wire required. In +addition, about two pounds of paraffin and a pad of linen paper or +typewriter paper will be required. The wire may be either enamel, +cotton, or silk insulated. Single silk-covered wire is preferred. + + + ────────────────────────────────────────────────────────────────── + SIZE OF COIL SIZE OF WIRE AMOUNT + ────────────────────────────────────────────────────────────────── + 1/2 inch 36 B. & S. 10 ounces + ────────────────────────────────────────────────────────────────── + 1 inch 34 B. & S. 1 lb. + ────────────────────────────────────────────────────────────────── + 1/2 inch 34 B. & S. 2 lbs. + ────────────────────────────────────────────────────────────────── + + +The means for supporting and turning the coil in order to wind on the +secondary may be left somewhat to the ingenuity of the young +experimenter. The following suggestion, however, is one which experience +has proved to be well worth following out, and may be applied to other +things than the construction of an induction coil. It seems to be the +nature of most boys, for some reason or other, to be unwilling to spend +time and labor on anything which will aid them in their work. They are +always in such a hurry and so anxious to see something completed that +they direct all their energy to that end rather than spend part of their +time in constructing some little device which would really lighten the +other work and go a long way towards insuring its successful completion. + +I have frequently given instructions for building an induction coil and +placed particular stress upon winding the secondary, only to have such +suggestions ignored in the anxious endeavor of boys to finish the coil +as soon as possible. In every such instance the coil has been a failure. + +[Illustration: Fig. 162.—Simple Winding Device for winding the +Secondary.] + +The illustration shows a simple form of winder, with which the operation +of winding the secondary is a very slow one, but, on the other hand, it +is possible to do very accurate, careful winding with the aid of such a +device. The parts may all be made from wood. + +The chucks fit tightly over the ends of the core so that when the handle +is turned, the coil will revolve also. The spring serves to keep the +chucks snugly against the coil ends, so that they will not slip. + +From one-half to five-eighths of a pound of wire will be required to +wind the coil. A large number of strips of thin paraffined or waxed +paper must be cut five inches wide. The inside terminal, or "beginning" +end of the wire is tied around the insulating tube near the left-hand +end. The spool of wire must be placed in a position where it will +revolve freely without strain on the wire. No. 36 is very fine and +easily broken, so use the utmost care to guard against this mishap. + +[Illustration: Fig. 163.—Completed Secondary Winding.] + +Wind on a smooth, even layer of wire, permitting each turn to touch the +other, but none to lap over. Carry the winding to within one-half inch +of the ends of the insulating tube and then wind on two layers of the +waxed paper. + +The paper must be put on smoothly and evenly, so as to afford a firm +foundation for the next layer. The wire is wrapped around with the +paper, so that the next layer starts one-half inch from the edge. A +second layer is then wound on very carefully, stopping when it comes +one-half inch from the edge. Two more layers of paper are put on, and +the process repeated, alternately winding on paper and wire until the +stated quantity of the latter has been used up. The layers of wire may +occasionally be given a coating of shellac. This is a good insulator, +and will serve to hold them together and prevent the wire from becoming +loose. + +In winding the coil, remember that if at any point you allow the winding +to become irregular or uneven, the irregularity will be much exaggerated +on the succeeding layers. For this reason, do not allow any to occur. If +the wire tends to go on unevenly, wrap an extra layer of thick paper +around underneath so as to offer a smooth foundation, and you will find +the difficulty remedied. + +[Illustration: Fig. 164.—Interrupter Parts.] + +An efficient vibrator for a coil cannot be easily made, and it is best +to buy one which is already fitted with platinum points. The interrupter +will play a very important part in the successful working of the coil, +and its arrangement and construction are important. Interrupters like +that shown in the illustration and used for automobile will be found the +best. + +The condenser may be home-made. It consists of alternate sheets of +tinfoil and paraffined paper, arranged in a pile as shown in the +illustration. The following table gives the proper sizes for condensers +for three different coils. + + + ────────────────────────────────────────────────────────────────── + TINFOIL + SIZE OF SPARK-COIL ─────────────────────────────────────────── + NO. SHEETS SIZE OF SHEETS + ────────────────────────────────────────────────────────────────── + 1/2 inch 50 2 x 2 + ────────────────────────────────────────────────────────────────── + 1 inch 100 7 x 5 + ────────────────────────────────────────────────────────────────── + 1 1/2 inch 100 8 x 6 + ────────────────────────────────────────────────────────────────── + + +The paper must be about one-half inch larger all the way around, so as +to leave a good margin. The alternate sheets of tinfoil, that is, all on +one side and all on the other, are connected. + +The condenser is connected directly across the terminals of the +interrupter. + +[Illustration: Fig. 165.—Condenser.] + +There are various methods of mounting a coil, the most common being to +place it in a box with the interrupter at one end. Perhaps, however, one +of the neatest and also the simplest methods is to mount it in the +manner shown in the illustration. + +The end-pieces are cut out of wood. No specific dimensions can be given, +because the diameter of the coils will vary somewhat according to who +winds them and how tightly they are made. The coil is enclosed in a tube +made by rolling up a strip of cardboard and then giving it a coat of +shellac. The tube may be covered by a strip of black cloth, so as to +improve its appearance. + +[Illustration: Fig. 166.—Completed Coil.] + +The vibrator is mounted on the end. The core projects through a hole in +the wood near the end of the vibrator spring so that the latter will be +drawn in by the magnetism of the core when the current flows. The +condenser may be placed in the hollow box which forms the base of the +coil. + +The secondary terminals of the coil are mounted on a small strip of wood +bridging the two coil ends. + +One terminal of the primary is connected to a binding-post mounted on +the base, and the other led to the vibrator spring. The vibrator yoke is +connected to a second binding-post on the base. One terminal of the +condenser is connected to the spring, and the other to the yoke. + +Four cells of dry battery should be sufficient to run the coil and cause +it to give a good one-half-inch spark if built according to the +directions here given. The vibrator or interrupter will require +adjusting and a position of the adjusting screw will soon be found where +the coil works best. + + +Experiments with a Spark-Coil + + +*Electrical Hands.* Many extraordinary and interesting experiments may +be performed with the aid of a spark-coil. + +The following experiment never fails to amuse a party of friends, and is +mystifying and weird to the ordinary person, unacquainted with the +secret of its operation. + +Figure 167 shows the arrangement of the apparatus. The primary of an +ordinary one-inch spark induction coil is connected in series with a +twelve-volt battery and telephone transmitter. A small switch is +included in the circuit to break the current and prevent needless waste +of the battery when the apparatus is not in immediate use. The secondary +terminals of the induction coil are led by means of an insulated wire to +the adjoining room where they terminate in a pair of scissors, or some +other small metallic object which may be clasped in the hand. + +Each of two persons, wearing dry shoes or rubber-soled slippers, grasps +the terminal of one wire in one hand. The other hand is placed flat +against the ear of a third person, with a piece of dry linen paper +intervening between the hands and the head. If a fourth person, in the +room where the induction coil is located, then closes the small switch +and speaks into the telephone transmitter, the person against whose ears +the hands are being held will hear the speech very distinctly. The +ticking of a watch held against the mouthpiece of the transmitter will +be heard with startling clearness. + +[Illustration: Fig. 167.—Diagram showing how to connect the Apparatus +for the "Electric Hands" Experiment.] + +The principle governing the operation of the apparatus is very simple. +Almost every experimenter is familiar with the ordinary electrical +condenser, which consists of alternate sheets of paraffined paper and +tinfoil. When this is connected to a source of electricity of high +potential, but not enough so as to puncture the paper dielectric, the +alternate sheets of tinfoil will become oppositely charged and attract +each other. If the circuit is then broken the sheets will lose their +charge and also their attraction for one another. If the tinfoil sheets +and paper are not pressed tightly together, there will be a slight +movement of the tinfoil and paper which will correspond in frequency to +any fluctuations of the charging current which may take place. + +The head of the third person and the hands held against his head act +like three tinfoil sheets of a condenser, separated by two sheets of +paper. The words spoken in the transmitter cause the current to +fluctuate and the induction coil raises the potential of the current +sufficiently to charge the condenser and cause a slight vibration of the +paper dielectric. The vibrations correspond in strength and speed to +those of the voice, and so the words spoken in the transmitter are +audible to the person over whose ears the paper is pressed. + +Everything about the apparatus must be as dry as possible, to insure its +successful operation. The people holding the wires in their hands should +stand on a carpeted floor. Always be very careful to tighten the +adjusting screw and block the interrupter on the coil, so that by no +means can it possibly commence to operate, or the person listening, +instead of "hearing things" will become the victim of a rather painful, +practical joke. + + +Geissler Tubes + + +The most beautiful and surprising effects may be obtained by lighting +Geissler tubes with a coil. The tubes are made in intricate and varied +patterns of special glass, containing fluorescent minerals and salts, +and are filled with different rarefied gases. When the tubes are +connected to the secondary of a spark-coil by means of a wire fastened +to the little rings at the end, and the coil is set in operation, they +light up in the most wonderful way imaginable. The rarefied gases and +minerals in the glass throw out beautiful iridescent colors, lighting up +a dark room with a weird flickering light. Every tube is usually of a +different pattern and has a combination of different colors. The most +beautiful tubes are those provided with a double wall containing a +fluorescent liquid, which heightens the color effects when the tube is +lighted. + +[Illustration: Fig. 168.—Geissler Tubes.] + +Eight to ten tubes may be lighted at once on an ordinary coil by +connecting them in series. + + +Ghost Light + + +If you grasp the bulb of an old incandescent electric lamp in one hand +and touch the base to one side of the secondary when the coil is in +operation the bulb will emit a peculiar greenish light in the dark. + + +Puncturing Paper + + +If you place a piece of heavy paper or cardboard between two sharp wires +connected to the secondary of a spark-coil and start the coil working, +the paper will be pierced. + + +A Practical Joke + + +This action of the coil may be made the basis of an amusing joke. Offer +a friend who may smoke cigarettes some cigarette paper which has been +prepared in the following way. + +[Illustration: Fig. 169.—The Bulb will emit a Peculiar Greenish Light.] + +Place several sheets of the paper on a piece of sheet-metal which is +connected to one side of the secondary. By means of an insulated handle +so that you will not get a shock, move the other wire all over the +surface of the cigarette paper. The paper will be pierced with numerous +fine holes which are so fine that they can hardly be seen. + +If your friend uses any of the paper in making a cigarette and tries to +light it he will waste a box of matches without being able to get one +good puff, because the little invisible holes in the paper will spoil +the draft. Perhaps he may quit smoking altogether. + + +An Electric Garbage-can + + +[Illustration: Fig. 170.—An Electrified Garbage-can.] + +If there are any dogs in your neighborhood that have a habit of +extracting things from your ash-barrel or garbage-can, place the latter +on a piece of dry wood. Lead a well insulated wire from one secondary +terminal of your coil to the can. Ground the other secondary terminal. +If you see a dog with his nose in the can press your key and start the +coil working. It will not hurt the dog, but he will get the surprise of +his life. He will go for home as fast as he can travel and will not +touch that particular can again, even if it should contain some of the +choicest canine delicacies. + + +Photographing an Electric Discharge + + +The following experiment must be conducted in a dark room with the aid +of a ruby photographic lamp, as otherwise the plates used would become +lightstruck and spoiled. + +[Illustration: Fig. 171.—Jacob’s Ladder.] + +Placed an ordinary photographic plate on a piece of sheet-metal with the +coated side of the plate upwards. Connect one of the secondary terminals +of the spark-coil to the piece of sheet-metal. + +Then sift a thin film of dry starch powder, sulphur, or talcum through a +piece of fine gauze on the plate. Lead a sharp-pointed wire from the +other secondary terminal of the coil to the center of the plate and then +push the key just long enough to make one spark. + +Wipe the powder off the plate and develop it in the usual manner of +films and plates. If you cannot do developing yourself, place the plate +back in its box and send it to some friend, or to a photographer. + +The result will be a negative showing a peculiar electric discharge, +somewhat like sea-moss in appearance. No two such photographs will be +alike and the greatest variety of new designs, etc., imaginable may be +produced in this manner. + + +Jacob’s Ladder + + +Take two pieces of bare copper wire about eight inches long and bend +them at right angles. Place them in the secondary terminals of a +spark-coil as in Figure 171. Bend them so that the vertical portions are +about one-half of an inch apart at the bottom and one inch apart at the +top. Start the coil working, and the sparks will run up the wires from +the bottom to the top and appear very much like the rungs in a ladder. + + +X-Rays + + +Most young experimenters are unaware what a wonderful and interesting +field is open to the possessor of a small X-ray tube. + +Small X-ray tubes which will operate satisfactorily on an inch and +one-half spark-coil may be obtained from several electrical supply +houses. They usually cost about four dollars and a half. With such a +tube and a _fluoroscope_ it is possible to see the bones in the human +hand, the contents of a closed purse, etc. + +The tube is made of glass and contains a very high vacuum. The long end +of the tube contains a platinum electrode called the _cathode_. The +short end contains two electrodes called _anodes_, one perpendicular to +the tube and the other diagonal. + +The tube is usually clamped in a wooden holder called an X-ray tube +stand. The tube should be so adjusted that the X-rays which are +reflected from the diagonal anode will pass off in the direction shown +by the dotted lines in Figure 174. + +The fluoroscope is a cone-shaped wooden box fitted with a screen +composed of a sheet of paper covered with crystals of a chemical called +platinum-barium-cyanide. + +[Illustration: Fig. 172.—An X-Ray Tube.] + +The opposite end of the box is fitted with a covering of felt or velvet +which shuts off the light around the eyes and nose when you look into +the fluoroscope and hold it tightly against the face. + +A fluoroscope may be purchased complete, or the platinum-barium-cyanide +screen purchased separately and mounted on a box as shown in Figure 173. + +The two anodes of the tube should be connected, and led to one terminal +of a spark-coil capable of giving a spark at least one and one-half +inches long. Another wire should be led from the cathode of the tube to +the other terminal of the coil. + +[Illustration: Fig. 173.—Fluoroscope.] + +When it is desired to inspect any object, such as the hand, it must be +held close to the screen of the fluoroscope and placed between the +latter and the tube in the path of the X-rays. The X-rays are thrown +forth from the tube at an angle of 45 degrees from the diagonal anode. + +Look into the fluoroscope and it should appear to be filled with a green +light. If not, the battery terminals connected to the primary of the +coil should be reversed, so as to send the current through in the +opposite direction. + +The X-rays will cause the chemicals on the screen to light up and give +forth a peculiar green light. If the hand is held against the screen, +between the screen and the tube, the X-rays will pass through the hand +and cast a shadow on the screen. They do not pass through the bones as +easily as they do through the flesh and so will cast a shadow of the +bones in the hand on the screen, and if you look closely you will be +able to see the various joints, etc. The interrupter on the coil should +be carefully adjusted so that the light does not flicker too much. + +[Illustration: Fig. 174.—How to connect an X-Ray Tube to a Spark-Coil.] + +If it is desired to take X-ray pictures, a fluoroscope is unnecessary. + +Turn the tube around so that the X-rays point downward. + +Shut the battery current off so that the tube is not in operation until +everything else is ready. + +Place an ordinary photographic plate, contained in an ordinary +plate-holder, directly under the tube with the gelatin side of the plate +upwards. + +Place the hand flat on the plate and lower the tube until it is only +about three inches above the hand. Then start the coil working so that +the tube lights up and permit it to run for about fifteen minutes +without removing the hand. Then turn the current off and develop the +plate in a dark room. + +It is possible to obtain a very good X-ray photograph of the hand in +this manner. Photographs showing the skeleton of a mouse, nails in a +board, coins in a purse, a bullet in a piece of wood, etc., are a few of +the other objects which make interesting pictures. + +[Illustration: An X-Ray Photograph of the hand taken with the Outfit +shown in Figure 174. The arrows point to injuries to the bone of the +third finger near the middle Joint Resulting in a Stiff Joint.] + + + +CHAPTER XIII TRANSFORMERS + + +In most towns and cities where electricity for light and power is +carried over long distances, it will be noticed that small iron boxes +are fastened to the poles at frequent intervals, usually wherever there +is a group of houses or buildings supplied with the current. Many boys +know that the boxes contain "transformers," but do not quite understand +exactly what their purpose is, and how they are constructed. + +When it is desired to convey electrical energy to a distance, for the +purpose of producing either light or power, one of the chief problems to +be faced is, how to reduce to a minimum any possible waste or loss of +energy during its transmission. Furthermore, since wires and cables of +large size are very costly, it is desirable that they be as small as +possible and yet still be able to carry the current without undue +losses. + +It has already been explained that wires offer resistance to an +electrical current, and that some of the energy is lost in passing +through a wire because of this resistance. Small wires possess more +resistance than large ones, and if small wires are to be used, in order +to save on the cost of the transmission line, the loss of energy will be +greater, necessitating some method of partially reducing or overcoming +this fault. + +In order to explain clearly how the problem is solved, the electric +current may for the moment be compared to a stream of water flowing +through a pipe. + +[Illustration: Fig. 175.—Comparison between Electric Current and Flow of +Water.] + +The illustration shows two pipes, a small one and a large one, each +supposed to be connected to the same tank, so that the pressure in each +is equal, and it is clearly apparent that more water will flow out of +the large one than out of the small one. If ten gallons of water flow +out of the large pipe in one minute, it may be possible that the +comparative sizes of the pipes are such that only one gallon of water +will flow out of the small one in the same length of time. + +But in case it should be necessary or desirable to get ten gallons of +water a minute out of a small pipe such as _B_, what could be done to +accomplish it? + +The pressure could be increased. The water would then be able better to +overcome the resistance of the small pipe. + +This is exactly what is done in the distribution of electric currents +for power and lighting. The pressure or potential is increased to a +value where it can overcome the resistance of the small wires. + +But unfortunately it rarely happens that electrical power can be +utilized at high pressure for ordinary purposes. For instance, 110 volts +is usually the maximum pressure required by incandescent lamps, whereas +the pressure on the line wires issuing from the power-house is generally +2,200 volts or more. + +Such a high voltage is hard to insulate, and would kill most people +coming into contact with the lines, and is otherwise dangerous. + +Before the current enters a house, therefore, some apparatus is +necessary, which is capable of reducing this high pressure to a value +where it may be safely employed. + +This is the duty performed by the "transformer" enclosed in the black +iron box fastened on the top of the electric light poles about the +streets. + +If a transformer were to be defined it might be said to be a device for +changing the voltage and current of an _Alternating_ circuit in pressure +and amount. + +The word, _alternating_, has been placed in italics because it is only +upon alternating currents that a transformer may be successfully +employed. Therein, also, lies the reason why alternating current is +supplied in some cases instead of direct current. It makes possible the +use of transformers for lowering the voltage at the point of service. + +Many boys possessing electrical toys and apparatus operating upon direct +current only, have bemoaned the fact that the lighting system in their +town furnished alternating current. Very often in the case of small +cities or towns one power-house furnishes the current for several +communities and the energy has to be carried a considerable distance. +Alternating current is then usually employed. + +[Illustration: Fig. 176.—Alternating Current System for Light and +Power.] + +The illustration shows the general method of arranging such a system. A +large dynamo located at the power-house generates alternating current. +The alternating current passes into a "step-up" transformer which raises +the potential to 2,200 volts (approximately). It is then possible to use +much smaller line wires, and to transmit the energy with smaller loss +than if the current were sent out at the ordinary dynamo voltage. The +current passes over the wires at this high voltage, but wherever +connection is established with a house or other building, the "service" +wires which supply the house are not connected directly to the line +wires, but to a a "step-down" transformer which lowers the potential of +the current flowing into the house to about 110 volts. + +In larger cities where the demand for current in a given area is much +greater than that in a small town, a somewhat different method of +distributing the energy is employed. + +[Illustration: Fig. 177.—Motor Generator Set for changing Alternating +Current to Direct Current.] + +The alternating current generated by the huge dynamos at the "central" +station is passed into a set of transformers which in some cases raise +the potential as high as five or six thousand volts. The current is then +sent out over cables or "feeders" to various "sub" stations, or +"converter" stations, located in various parts of the city. Here the +current is first sent through a set of step-down transformers which +reduce the potential to the approximate value originally generated by +the dynamos. It then passes into the "rotary converters" which change +the alternating current into direct current after which it is sent by +underground cables direct to the consumers in the neighborhood. + +A transformer in its simplest form consists of two independent coils of +wire wound upon an iron ring. When an alternating current is passed +through one of the coils, known as the primary, it produces a magnetic +field which induces a current of electricity in the other, or secondary, +coil. + +The potential or voltage of the current in the secondary is in nearly +the same ratio to the potential of the current passed into the primary +as the number of turns in the secondary is to the number of turns in the +primary. + +[Illustration: Fig. 178.—Step-Up Transformer.] + +Knowing this, it is very easy to arrange a transformer to "step" the +potential up or down as desired. The transformer in Figure 178 +represents a "step-up" transformer having ten turns of wire on the +primary and twenty turns on the secondary. If an alternating current of +10 volts and 2 amperes is passed into the primary, the secondary winding +will double the potential, since it has twice as many turns as the +primary and the current delivered by the secondary will be approximately +20 volts and 1 ampere. + +The action may be very easily reversed and a "step-down" transformer +arranged by placing twenty turns of wire on the primary and ten turns on +the secondary. If a current of 20 volts and 1 ampere is passed into the +primary, the secondary will deliver a current of only 10 volts and 2 +amperes, since it contains only half as many turns. + +A circular ring of iron wire wound with two coils would in many respects +be somewhat difficult to construct, and so the iron core is usually +built in the form of a hollow rectangle and formed of sheets of iron. + +[Illustration: Fig. 179.—Step-Down Transformer.] + +It is often desirable to have at hand an alternating current of low +voltage for experimental purposes. Such a current may be used for +operating induction coils, motors, lamps, toy railways, etc., and is +quite as satisfactory as direct current for many purposes, with the +possible exception of electro-plating and storage-battery charging, for +which it cannot be used. + +When the supply is drawn from the 110-volt lighting circuit and passed +through a small "step-down" transformer, the alternating current is not +only cheaper but more convenient. A transformer of about 100 watts +capacity, capable of delivering a current of 10 volts and 10 amperes +from the secondary will not draw more than approximately one ampere from +the 110-volt circuit. This current is only equal to that consumed by two +ordinary 16-candle-power lamps or one of 32 candle-power, making it +possible to operate the transformer to its full capacity for about one +cent an hour. A further advantage is the fact that a "step-down" +transformer enables the small boy to use the lighting current for +operating electrical toys without danger of receiving a shock. + +[Illustration: Fig. 180.—Core Dimensions.] + +The transformer described in the following pages can be easily built by +any boy at all familiar with tools, and should make a valuable addition +to his electrical equipment, provided that the directions are carefully +followed and pains are taken to make the insulation perfect. + +The capacity of the transformer is approximately 100 watts. The +dimensions and details of construction described and illustrated are +those of a transformer intended for use upon a lighting current of 110 +volts and 60-cycles frequency. The frequency of most alternating current +systems is 25, 60, or 120 cycles. The most common frequency is 60. +Dimensions and particulars of transformers for 25 and 120 cycles will be +found in the form of a table farther on. + +The frequency of your light circuit may be ascertained by inquiring of +the company supplying the power. + +[Illustration: Fig. 181.—The Core, Assembled and Taped.] + +The first part to be considered in the construction of a transformer is +the core. The core is made up of thin sheet-iron strips of the +dimensions shown in Figure 180. The iron may be secured from almost any +hardware store or plumbing shop by ordering "stove-pipe iron." Have the +iron cut into strips 1 1/4 inches wide and 24 inches long. Then, using a +pair of tinner’s shears, cut the long strips into pieces 3 inches and 4 +3/4 inches long until you have enough to make a pile of each 2 1/2 +inches high when they are stacked up neatly and compressed. The long +strips are used to form the "legs" of the core, and the short ones the +"yokes." + +[Illustration: Fig. 182.—Transformer Leg.] + +The strips are assembled according to the diagram shown in Figure 180. +The alternate ends overlap and form a hollow rectangle 4 1/4 x 6 inches. +The core should be pressed tightly together and the legs bound with +three or four layers of insulating tape preparatory to winding on the +primary. After the legs are bound, the yoke pieces may be pulled out, +leaving the legs intact. + +Four fiber heads, 2 1/2 inches square and 1/8 of an inch thick, are made +as shown in Figure 183. A square hole 1 1/4 x 1 1/4 inches is cut in the +center. Two of these are placed on each of the assembled legs as shown +in Figure 184. + +[Illustration: Fig. 183.—Fiber Head.] + +The primary winding consists of one thousand turns of No. 20 B. & S. +gauge single-cotton-covered magnet wire. Five hundred turns are wound on +each leg of the transformer. The wire should be wound on very smoothly +and evenly with a layer of shellacked paper between each layer of wire. + +The two legs should be connected in series. The terminals are protected +and insulated by covering with some insulating tape rolled up in the +form of a tube. + +The secondary winding consists of one hundred turns of No. 10 B. & S. +gauge double-cotton-covered wire. Fifty turns are wound on each leg, +over the primary, several layers of paper being placed between the two. + +[Illustration: Fig. 184.—Leg with Heads in Position for Winding.] + +A "tap" is brought out at every ten turns. The taps are made by +soldering a narrow strip of sheet-copper to the wire at proper +intervals. Care must be taken to insulate each joint and tap with a +small strip of insulating tape so that there is no danger of a short +circuit being formed between adjacent turns. + +After the winding is completed the transformer is ready for assembling. +The yoke pieces of the core should be slipped into position and the +whole carefully lined up. The transformer itself is now ready for +mounting. + +[Illustration: Fig. 185.—How to make a Tap in the Primary by soldering a +Copper Strip to the Wire.] + +The base-board measures 11 x 7 3/4 x 7/8 inches. It is shown in Figure +192. + +The transformer rests upon two wooden strips, _A_ and _B_, 4 1/4 inches +long, 1 1/4 inches wide, and 3/4 of an inch high. The strips are nailed +to the base so that they will come under the ends of the core outside of +the fiber heads. + +The transformer is held to the base by two tie-rods passing through a +strip, _C_, 6 inches long, one-half of an inch thick and three-quarters +of an inch wide. The strip rests on the ends of the core. The tie-rods +are fastened on the under side of the base by means of a nut and washer +on the ends. When the nuts are screwed up tightly, the cross-piece will +pull the transformer firmly down to the base. + +[Illustration: Fig. 186.—The Transformer completely Wound and ready for +Assembling.] + +The regulating switches, two in number, are mounted on the lower part of +the base. The contact points and the arm are cut out of sheet-brass, +one-eighth of an inch thick. It is unnecessary to go into the details of +their construction, because the dimensions are plainly shown in Figure +188. + +The contacts are drilled out and countersunk so that they may be +fastened to the base with small flat-headed wood screws. + +Each switch-arm is fitted with a small rubber knob to serve as a handle. +The arm works on a small piece of brass of exactly the same thickness as +the switch-points. Care must be taken that the points and this washer +are all exactly in line, so that the arm will make good contact with +each point. There are five points to each switch, as shown in Figure +190. + +[Illustration: Fig. 187.—Wooden Strips for mounting the Transformer on +the Base.] + +The switch, _D_, is arranged so that each step cuts in or out twenty +turns of the secondary, the first point being connected with the end of +the winding. The second point connects with the first tap, the third +contact with the second tap, the fourth contact with the third tap, and +the fifth contact with the fourth tap. + +[Illustration: Fig. 188.—Details of the Switch Parts.] + +The switch, _E_, is arranged so that each step cuts in or out five +turns. The contacts on this switch are numbered in the reverse +direction. The fifth contact of switch _D_, and the fifth contact of +switch _E_, are connected together. The fourth contact is connected to +the fifth tap, the third contact to the sixth tap, the second contact to +the seventh, and the first contact to the end of the winding. + +This arrangement makes it possible to secure any voltage from one-half +to ten in one-half-volt steps from the secondary of the machine. Each +step on the switch, _D_, will give two volts, while those on _E_ will +each give one-half of a volt. + +[Illustration: Fig. 189.—The Complete Switch.] + +Two binding-posts (marked _P_ and _P_ in the drawing) mounted in the +upper corners of the base are connected to the terminals of the primary +winding. The two posts in the lower corners (marked _S_ and _S_ in the +drawing) are connected to the switch levers, and are the posts from +which the secondary or low voltage is obtained. + +[Illustration: Fig. 190.—Diagram of Connections.] + +The transformer may be connected to the 110-V. alternating current +circuit by means of an attachment plug and cord. One end of the cord is +placed in each of the primary binding-posts. The other end of the cord +is connected to the attachment plug so that the latter may be screwed +into any convenient electric-light socket. + +[Illustration: Fig. 191.—Top View of the Transformer.] + +The transformer must not be connected directly to the line. An +instrument such as this is not designed for continuous service and is +intended to be disconnected as soon as you are through using it. + +[Illustration: Fig. 192.—Side View of the Transformer.] + +It will be found a great convenience in operating many of the electrical +devices described, wherever direct current is not essential. + + + +CHAPTER VIV WIRELESS TELEGRAPHY + + +Probably no branch of electrical science ever appealed more to the +imagination of the experimenter than that coming under the heading of +wireless telegraphy. Wherever you go, you are likely to see the +ear-marks of _amateur_ wireless telegraph stations in the aerials and +masts set up in trees and on house-tops. It is estimated that there are +nearly a quarter of a million such stations in the United States. + +There is really no great mystery about this wonderful art which made +possible the instantaneous transmission of messages over immense +distances without any apparent physical connection save that of the +earth, air, or water. + +Did you ever throw a stone in a pool of water? As soon as the stone +struck, little waves spread out from the spot in gradually enlarging +circles until they reached the shore or died away. + +By throwing several stones in succession, with varying intervals of time +between them, it would be possible so to arrange a set of signals, that +they would convey a meaning to a second person standing on the opposite +shore of the pool. + +Wireless telegraphy is based upon the principle of _creating and +detecting_ waves in a great _pool_ of ether. + +Modern scientists suppose that all space is filled with an "imaginary" +substance called _ether_. The ether is invisible, odorless, and +practically weightless. This ether, however, bears no relation to the +anaesthetic of that name which is used in surgical operations. + +It surrounds and penetrates all substances and all space. + +[Illustration: Fig. 193.—Little Waves spread out from the Spot.] + +It exists in a vacuum and in solid rocks. Since the ether does not make +itself apparent to any of our physical senses, some of these statements +may seem contradictory. Its definite existence cannot be proved except +by reasoning, but by accepting and imagining its reality, it is possible +to understand and explain many scientific puzzles. + +A good instance is offered by the sun. Light and heat can be shown to +consist of extremely rapid vibrations. That fact can be proved. The sun +is over 90,000,000 miles away from our earth and yet light and heat come +streaming down to us through a space that is devoid even of air. +Something must exist as a medium to transmit these vibrations; it is the +ether. + +Let us consider again the pool of water. The waves or ripples caused by +throwing in the stone are vibrations of the water. The distance between +two adjacent ripples is called the _wave length_. + +The distances between two vibrations of light can also be _measured_. +They are so small, however, that they may be spoken of only in +_thousandths_ of an inch. The waves created in the ether by wireless +telegraph apparatus are the same as those of light except that their +length usually varies from 75 to 9,000 _feet_ instead of a fraction of a +thousandth of an inch. + +[Illustration: Fig. 194.—A Simple Transmitter.] + +*A Simple Transmitter* is illustrated in Figure 194. A telegraph key is +connected in series with a set of cells and the _primary_ of an +induction coil, which, it will be remembered, is simply a coil +consisting of a few turns of wire. This induces a high voltage in a +second coil consisting of a larger number of turns and called the +_secondary_. + +The terminals of the secondary are led to a spark-gap—an arrangement +composed of two polished brass balls, separated by a small air-gap. One +of the balls, in turn, is connected to a metal plate buried in the +earth, and the other to a network of wires suspended high in the air and +insulated from all surrounding objects. + +When the key at the transmitter is pressed, the battery current flows +through the primary of the induction coil and generates in the secondary +a current of very high voltage, 20,000 volts or more, which is able to +jump an air-gap in the shape of a spark at the secondary terminals. The +latter are connected to the earth and aerial, as explained above. The +high potential currents are therefore enabled to charge the aerial. The +charge in the aerial exerts a great tendency to pass into the ground, +but is prevented from doing so by the small air-gap between the +spark-balls until the charge becomes so great that the air-gap is +punctured and the charge passes across and flows down into the ground. +The passage of the charge is made evident by the spark between the two +spark-balls. + +The electrical charges flowing up and down the aerial disturb the ether, +strike it a blow, as it were. The effect of the blow is to cause the +ether to vibrate and to send out waves in all directions. It may be +likened to the pond of water which is suddenly struck a blow by throwing +a stone into it, so that ripples are immediately sent out in widening +circles. + +*These Waves in the Ether* are called electro-magnetic or _Hertzian_ +waves, after their discoverer, Hertz. The distance over which they pass +is dependent upon the power of the transmitting station. The waves can +be made to correspond to the dots and dashes of the telegraphic code by +so pressing the key. If some means of detecting the waves is employed we +may readily see how it is possible to send wireless messages. + +*The Action of the Receiving Station* is just the opposite of that of +the transmitter. When the waves pass out through the ether, some of them +strike the aerial of the receiving station and generate a charge of +electricity in it which tends to pass down into the earth. If the +transmitting and receiving stations are very close together and the +former is very powerful, it is possible to make a very small gap in the +receiving aerial across which the charge will jump in the shape of +sparks. Thus the action of the receptor simply takes place in a reversed +order from that of the transmitter. + +If the stations are any considerable distance apart, it is impossible +for the currents induced in the receiving aerial to produce sparks, and +so some more sensitive means of detecting the waves from the transmitter +is necessary, preferably one which makes itself evident to the sense of +hearing. + +The telephone receiver is an extremely sensitive instrument, and it only +requires a very weak current to operate it and produce a sound. The +currents or _oscillations_ generated in the aerial, however, are +alternating currents (see pages 97-99) of _high frequency_, that is, +they flow in one direction and then reverse and flow in the other +several thousand times a second. Such a current cannot be made to pass +through a telephone receiver, and in order to do so the nature of the +current must be changed by converting it into direct current flowing in +one direction only. + +Certain minerals and crystals possess the remarkable ability to do this, +_silicon_, galena, and iron pyrites are among the best. + +[Illustration: Fig. 195.—A Simple Receptor.] + +The diagram in Figure 195 shows the arrangement of a simple receiving +outfit. The _detector_ consists of a sensitive mineral placed between +two contacts and connected so that the aerial currents must pass through +it on their way to the ground. A telephone receiver is connected to the +detector so that the _rectified currents_ (currents which have been +changed into direct current) pass into it and produce a sound. By +varying the periods during which the key is pressed at the transmitting +station, according to a prearranged code, the sounds in the receiver may +be made to assume an intelligible meaning. + + +HOW TO BUILD WIRELESS INSTRUMENTS + + +*The Aerial* + +Every wireless station is provided with a system of wires elevated high +in the air, above all surrounding objects, the purpose of which is to +radiate or intercept the electromagnetic waves, accordingly as the +station is transmitting or receiving. This system of wires is, as +already has been stated, called the _aerial_ or _antenna_. + +The arrangement of the aerial will greatly determine the efficiency and +range of the apparatus. + +The aerial should be as long as it is reasonably possible to make it, +that is from 50 to 150 feet. + +It will be necessary for most amateurs to put up their aerial in some +one certain place, regardless of what else may be in the vicinity, but +whenever possible the site selected should preferably be such that the +aerial will not be in the immediate neighborhood of any tall objects, +such as trees, smoke-stacks, telephone wires, etc., because such objects +will interfere with the aerial and noticeably decrease the range of the +station, both when transmitting and receiving. + +Bare copper wire makes the best aerials. Aluminum wire is very often +used and on account of its light weight causes very little strain on the +poles or cross arms. Iron wire should never be used for an aerial, even +if galvanized or tinned, because it tends to choke the currents which +must flow up and down the aerial when the station is in operation. + +[Illustration: Fig. 196.—Molded Aerial Insulator] + +The aerial must be very carefully insulated from its supports and all +surrounding objects. The insulation must be strong enough to hold the +weight of the aerial and able to withstand any strain caused by storms. + +Special aerial insulators made of molded insulating material and having +an iron ring imbedded in each end are the best. + +[Illustration: Fig. 197.—A Porcelain Cleat will make a Good Insulator +for Small Aerials.] + +Ordinary porcelain cleats may be used on small aerials where the strain +is light. + +One insulator should be placed at each end of each wire close to the +spreader or spar. + +Most aerials are made up of four wires. The wires should be placed as +far apart as possible. + +There are several different forms of aerials, the principal ones of +which are shown in Figure 199. They are known as the grid, “V," inverted +“L,” and “T” types. + +Most amateurs support their aerials from a pole placed on the top of the +house, in a tree, or erected in the yard. Many use two supports, since +such an aerial has many advantages. The facilities to be had for +supporting the aerial will largely determine which form to use. + +[Illustration: Fig. 198.—Method of Arranging the Wires and Insulating +them from the Cross Arm or Spreader.] + +The grid aerial has no particular advantages or disadvantages. + +The “V” aerial receives waves much better when they come from a +direction opposite to that in which the free end points. The "free" end +of the aerial is the one not leading into the station. + +The inverted “L” aerial possesses the same characteristics as the “V” +type. + +The “T” aerial is the best “all around" and is to be recommended +whenever it is possible to put up an aerial of this sort. + +Much of the detail of actually putting up an aerial or antenna must be +omitted, because each experimenter will usually meet different +conditions. + +It should be remembered, however, that the success of the whole +undertaking will rest largely upon the construction of a proper aerial. +The most excellent instruments will not give very good results if +connected to a poor aerial, while, on the other hand, inferior +instruments will often give fair results when connected to a good +aerial. + +[Illustration: Fig. 199.—Various Types of Aerials.] + +The aerial should be at least thirty feet high. + +The wire should not be smaller than No. 14 B. & S. + +The masts which support the aerial should be of wood and provided with +pulleys so that the wires may be lowered any time it may be necessary. +The mast should be thoroughly braced with stays or guys so as to +counteract the strain of the aerial. + +The aerial should not be hoisted up perfectly tight, but should be +allowed to hang somewhat loose, as it will then put less strain on the +ropes and poles that support it. + +When an aerial is to be fastened in a tree, it is best to attach it to a +pole placed in the top of the tree, so that it will come well above any +possible interference from the branches. + +The wires leading from the aerial to the instruments should be very +carefully insulated throughout their length. This part of the aerial is +called the "rat-tail" or lead-in. + +The illustrations in Figure 199 show the proper place to attach the +“lead-in" form of aerial. The wires should gradually converge. + +[Illustration: Fig. 200.—A Ground Clamp for Pipes.] + +It is very important that a good ground connection be secured for +wireless instruments. A good ground is absolutely necessary for the +proper working of the apparatus. Amateur experimenters usually use the +water or gas-pipes for a ground, and fasten the wires by means of a +ground clamp such as shown in Figure 200. In the country, where such +pipes are not available, it is necessary to bury a sheet of copper, +three or four feet square, in a moist spot in the earth and connect a +wire to it. + +*The Receiving Apparatus* + +The receiving instruments form the most interesting part of a wireless +station and usually receive first attention from the amateurs. They are +the ears of the wireless station and are wondrously sensitive, yet are +very simple and easy of construction. + +The instruments necessary for receiving are: + +A Detector, + +A Tuning Coil or a Loose Coupler, + +A Fixed Condenser, + +A Telephone Receiver. + +Other devices, such as a test buzzer, variable condenser, etc., may be +added and will improve the outfit. + +After the aerial has been properly erected, the first instrument +necessary to construct will be either a tuning coil or a loose coupler. +It is a good plan to make a tuning coil first, and a loose coupler after +you have had a little experience with your apparatus. + +*A Tuning Coil* is a very simple arrangement making it possible to +receive messages from greater distances, and also somewhat to eliminate +any messages not desirable and to listen without confusion to the one +wanted. + +A tuning coil consists of a single layer of wire wound upon a cylinder +and arranged so that connection may be had with any part of it by means +of sliding contacts. + +The cylinder upon which the wire is wound is a cardboard tube six and +three-quarters inches long and two and seven-eighths inches in diameter +outside. It should be given two or three coats of shellac both inside +and out so that it is thoroughly impregnated, and then laid away until +dry. This treatment will prevent the wire from becoming loose after the +tube is wound, due to shrinkage of the cardboard. + +[Illustration: Fig. 201.—Details of the Tuning Coil.] + +After having become dry, the tube is wound with a single layer of No. 25 +B. & S. gauge green silk or cotton-covered magnet wire. The wire must be +wound on very smoothly and tightly, stopping and starting one-quarter of +an inch back from each end. The ends of the wire are fastened by weaving +back and forth through two small holes punched in the cardboard tube +with a pin. + +The winding should be given a single coat of clear varnish or white +shellac and allowed to dry. + +The coil heads or end pieces are cut from one-half-inch wood according +to the plan and dimensions shown in the accompanying illustration. + +The top corners are beveled and notched to receive the slider-rods. A +circular piece of wood two and five-eighths inches in diameter and +three-eighths of an inch thick is nailed to the inside of each of the +coil heads to support the ends of the cylinder. + +The wooden parts should be stained mahogany or some other dark color and +finished with a coat of shellac or varnish. + +The slider-rods are square brass 3-16 x 3-16 inches and seven and +three-quarters inches long. A small hole is bored near the ends of each, +one-quarter of an inch from the edge, to receive a round-headed brass +wood screw which holds the rod to the tuner end. + +The sliders may be made according to the plan shown in Figure 201. + +The slider is made from a small piece of brass tubing, three-sixteenths +of an inch square. An 8-32 flat-headed brass screw is soldered to one +face, in the center. A small strip of phosphor bronze sheet or spring +copper soldered to the bottom of the slider forms a contact for making +connection to the wire on the cylinder. A small "electrose" knob screwed +to the slider makes a neat and efficient handle. + +Two sliders are required, one for each rod. + +The tuning coil is assembled as shown in Figure 203. The cardboard tube +is held in place by several small brass nails driven through it into the +circular pieces on the coil heads. + +A slider is placed on each of the slider-rods and the rods fastened in +the slots in the coil ends by a small round-headed brass screw, passing +through the holes bored near the ends for that purpose. + +[Illustration: Fig. 202.—Side and End Views of the Tuning Coil.] + +Two binding-posts are mounted on one of the coil ends. One should be +connected to each of the slider-rods. A third binding-post is placed +below in the center of the head and connected to one end of the wire +wound around the cylinder. + +A small, narrow path along the coil, directly underneath each slider and +to which the copper strip can make contact, must be formed by scraping +the insulation off the wire with a sharp knife. The sliders should make +contact with each one of the wires as they pass over, and should slide +smoothly without damaging or disarranging any of the wires. + +[Illustration: Fig. 203.—Complete Double-Slider Tuning Coil.] + +When scraping the insulation, be very careful not to loosen the wires or +remove the insulation from between them, so that they are liable to +short-circuit between adjacent turns. + +*A Loose Coupler* is a much more efficient tuning device than a +double-slider tuner, and sooner or later most amateur wireless operators +install one in their station. + +The loose coupler shown in the figure given on the next page is a very +simple one and is both easy and inexpensive to build. Its simplicity is +a disadvantage in one respect, however. Owing to its construction, it is +impossible to move the slider on the secondary when the latter is inside +the primary. The reason that I have chosen this sort of loose coupler to +describe is to acquaint my young readers with the methods of making a +loose coupler. + +The "Junior" loose coupler described farther on is a more elaborate +instrument of greater efficiency, but much harder to build. + +[Illustration: Fig. 204.—A Simple Loose Coupler.] + +The base of the loose coupler is of wood and measures twelve by four +inches. The head supporting the primary is of the same size as those +used on the "Junior" double-slide tuning coil just described. It may be +made in the same manner, and fitted with a circular block to support the +tube. The primary tube is of the same diameter as that on the tuning +coil but is only four inches long. It is fastened to the primary head +with glue and then secured with a number of small tacks. One or two +coats of shellac liberally applied will render it non-shrinkable, so +that the wire will not be apt to loosen after the loose coupler has been +in use a while. + +The secondary is of the same length as the primary, but of smaller +diameter, so that it will easily slip inside. It also is treated with +shellac. + +The primary should be wound with a single layer of No. 22 +single-silk-covered magnet wire. The secondary is wound with No. 29 +single-silk. + +The head supporting the secondary is smaller than that used for the same +purpose on the primary. The round boss to which the tube is fastened, +however, is much thicker. + +The secondary slides on a "guide-rod" supported at one end by passing +through the primary head and at the other by a brass upright. The +upright may also be made of wood. + +If the secondary is "offset," that is, placed out of center slightly to +one side, it will leave room so that the secondary slider will possibly +pass inside of the primary without striking. + +Both the primary and the secondary must be fitted with "sliders" to make +contact with the various turns of wire. + +The method of constructing a slider has already been described. + +The ends of the slider-rods are bent at right angles and fastened to the +coil heads by two small screws passing through holes bored near the +ends. A small narrow path must be scraped in the insulation under each +so that the slider will make contact with each turn. The secondary head +may be provided with a small electrose handle to facilitate sliding it +back and forth. + +Two binding-posts are mounted on each of the coil heads. + +One post on each is connected to the end of the coil farthest from the +head, and the other posts are each connected to the slider-rods. + +Figure 220 shows how to connect the loose coupler in the receiving set. + +In order to tune with a loose coupler, first adjust the slider on the +primary until the signals are the clearest. Then set the secondary +slider in the best place and move the secondary in and out of the +primary until the signals are clearest. + +*How to Build the Junior Loose Coupler* + +A loose coupler of the sort just described is simple and quite easily +constructed, but will not be found to work as well as one in which the +secondary may be varied by means of a switch while it is inside of the +primary. + +The base of the instrument measures twelve by three and five-eighths +inches. The primary is composed of a single layer of No. 24 B. & S. +gauge single-silk-covered wire wound on a cardboard tube two and +three-quarter inches in diameter and three and three-quarter inches +long. The winding is laid on in a single layer and should comprise about +150 turns. After winding on tightly, it should be given a coat of clean +white shellac and allowed to dry. The shellac is for the purpose of +fastening the wire down tightly to the tube so that it will not loosen +when the slider is moved back and forth. + +The primary is mounted between two heads, the details of which are shown +in Figure 205. One of the heads, _B_, has a flanged hole two and +three-quarter inches in diameter cut through the center so as to receive +the end of the tube and permit the secondary to pass inside. + +[Illustration: Fig. 205.—Details of the Wooden Parts.] + +The secondary winding is composed of a single layer of No. 28 B. & S. +gauge silk-covered wire and divided into six equal sections. The +secondary is supported by two circular wooden pieces, _C_ and _F_, and +slides back and forth on two guide-rods. The guide-rods should be brass. +Iron or steel rods running through the center of a loose coupler will +seriously weaken the signals, and such practice must by all means be +avoided. + +[Illustration: Fig. 206.—Side View of the Loose Coupler.] + +[Illustration: Fig. 207.—Top View of the Loose Coupler.] + +The secondary sections are connected to six contacts and a switch-arm +mounted on the end of the secondary so that by turning the switch either +one, two, three, four, five, or six sections of the winding may be +connected. + +[Illustration: Fig. 208.—End Views of the Loose Coupler.] + +[Illustration: Fig. 209.—Complete Loose Coupler.] + +The two binding-posts near the secondary end of the coupler are +connected to the terminals of the secondary winding by means of two +flexible wires. They have not been shown in several of the illustrations +because they would be liable to confuse the drawing. + +The primary is provided with a slider moving back and forth over a +narrow path scraped through the insulation so that it may make contact +with each wire independently. + +*Detectors* + +Detectors are very simple devices and consist merely of an arrangement +for holding a small piece of certain minerals and making a contact +against the surface. + +The crystal detector shown in Figure 210 is a very efficient form that +may be easily and quickly made. When finished, it will make a valuable +addition to almost any amateur experimenter’s wireless equipment. + +[Illustration: Fig. 210.—A Crystal Detector.] + +The bracket is bent out of a piece of strip brass about one-eighth of an +inch thick and five-eighths of an inch wide, according to the shape +shown in the illustration. The bracket is mounted on a circular wooden +base about three inches in diameter. The circular wooden blocks used by +electricians in putting up chandeliers, called “fixture blocks,” will +make a satisfactory base. An electrose knob of the typewriter type may +be purchased from any good dealer in wireless supplies. It should be +fitted with a threaded shank which will screw into a hole in the upper +part of the bracket. + +The mineral is contained in a small brass cup mounted on the base below +the end of the knob. + +Contact with the mineral in the cup is made by means of a fine wire +spring soldered to the end of the adjusting screw. + +Moving the screw up or down will vary the pressure of the spring on the +mineral and permit the most sensitive adjustment to be secured. The +bracket is connected to one of the binding-posts and the cup to the +other. + +[Illustration: Fig. 211.—Details of the Crystal Detector.] + +The detector shown in Figure 212 is of the type often termed a +"cat-whisker," because of the long, fine wire resting on the mineral. + +It consists of a small clip, formed by bending a strip of sheet-brass, +which grips a piece of galena. + +[Illustration: A Double Slider Tuning Coil.] + +[Illustration: A Junior Loose Coupler.] + +[Illustration: Crystal Detectors.] + +Galena may be obtained from any dealer in radio supplies. A piece of No. +30 phosphor bronze wire is soldered to the end of a short length of +brass rod supported by a binding post. The other end of the rod is +fitted with an electrose knob. This part of the detector is called the +"feeler." + +[Illustration: Fig. 212 Details of the "Cat Whisker" Detector.] + +The detector is fitted with binding posts and may be mounted upon any +suitable small base. The mineral clip is connected to one post and the +binding-post supporting the "feeler" to the other. The tension or +pressure of the end of the fine wire upon the mineral may be regulated +by twisting the electrose knob so as to twist the rod. The different +portions of the crystal may be "searched" for the most sensitive spot by +sliding the rod back and forth. + +A somewhat similar form of cat-whisker detector is shown in Figure 213. +It is provided with a cup to hold the mineral in place of a clip. + +The detector shown in Figure 214 is more elaborate than any of the +others described so far. + +[Illustration: Fig. 213.—Another Form of the "Cat-Whisker" Detector.] + +[Illustration: Fig. 214.—"Cat-Whisker" Detector.] + +The base is a wooden block, three and one-half by one and three-quarters +inches by one-half inch. The binding-posts are of the type commonly used +on electrical instruments. One of the posts is pivoted so that it will +swing from side to side. A short piece of brass rod fitted with a rubber +or fiber knob passes through the wire hole in the post. A piece of No. +30 B. & S. gauge bronze wire is soldered to the end of the rod. A small +brass cup contains the mineral, which may be either _galena_, or +_silicon_. By twisting the post and sliding the rod back and forth, any +portions of the mineral surface may be selected. + +*Fixed Condenser.* + +The construction of the condenser is illustrated in Figure 205. Take +twenty-four sheets of thin typewriter paper, three by four inches, and +twenty-three sheets of tinfoil, two by four inches. Pile them up, using +first a sheet of paper then a sheet of tinfoil, then paper, and so on, +so that every two sheets of tinfoil are separated by a sheet of paper. +Each sheet of tinfoil must, however, project out beyond the edge of the +paper. Connect all the tinfoil projections on one end of the condenser +together and and attach a small wire. Connect all those on the opposite +side in a similar manner. Then fasten a couple of rubber bands around +the condenser to hold it together. + +[Illustration: Fig. 215.—Building up a Fixed Condenser.] + +[Illustration: Fig. 216.—A Fixed Condenser enclosed in a Brass Case made +from a Piece of Tubing fitted with Wooden Ends.] + +If it is desired to give the condenser a finished appearance, it may be +placed in a brass tube fitted with two wooden or fiber ends. The ends +are provided with binding-posts to which the terminals of the condenser +are connected. + +*Telephone Receivers* for use with wireless instruments must be +purchased. Their construction is such that they cannot be made by the +experimenter. + +[Illustration: Fig. 217.—A Telephone Head Set.] + +A seventy-five ohm, double-pole telephone receiver will do for stations +not wishing to receive farther than fifty miles. + +In order to secure the best results from wireless instruments, it is +necessary to have receivers especially made for wireless. Each receiver +should have 1000 ohms resistance. Some boys may find it necessary to +purchase one receiver at a time. Two receivers, a double headband, and a +double cord, forming a complete head set as shown in Figure 217, should +be secured as soon as possible. + +[Illustration: Fig. 218.—A Circuit showing how to connect a +Double-Slider Tuning Coil.] + +*Connecting the Receiving Apparatus* + +Figure 218 shows how to connect a double-slide tuner, a detector, a +fixed condenser and a pair of telephones to the aerial and ground. The +same instruments with a loose coupler in place of the double-slide tuner +are shown in Figure 219. + +The diagrams in Figure 220 are the same circuits as those shown in +Figures 218 and 219, but show different instruments. + +[Illustration: Fig. 219.—Circuit showing how to connect a Loose +Coupler.] + +[Illustration: Fig. 220.—A Diagram showing how to connect some of the +Instruments described in this Chapter.] + +After the instruments are connected, place a piece of galena or silicon +in the cup of the detector and bring the wire down on it. Then move the +sliders on the tuning coil or loose coupler and adjust the detector +until you can hear a message buzzing in the telephones. It may require a +little patience and practice, but if you persist you will soon learn how +to adjust the apparatus so as to receive the signals loudly and clearly +with very little trouble. + +*The Transmitting Apparatus* + +Spark coils have already been described in Chapter XII. They may be used +to transmit wireless messages simply by connecting to a spark-gap and a +key. + +Spark coils which are especially made for wireless telegraphy will +usually send farther than an ordinary spark coil used for experimental +purposes. + +[Illustration: Fig. 221.—A Wireless Spark Coil.] + +A good one-inch coil costs from $4.50 to $5.00 and will send from three +to five miles if used with a fair aerial. + +A spark coil requires considerable current for its successful operation +and will give the best results if operated on storage cells, dry cells, +or bichromate cells. If dry cells are used, it is a good plan to connect +them in series multiple as shown in Figure 69. + +Spark-gaps may be made by mounting two double binding-posts on a wooden +base as shown in Figure 222. + +Zinc possesses some peculiar property which makes it very efficient for +a spark-gap, and for this reason the electrodes of a spark-gap are +usually zinc. + +[Illustration: Fig. 222.—Small Spark Gaps.] + +The figure shows two different forms of electrodes. In one, they are +made of zinc rods and provided with “electrose” handles. In the other +gap, the zinc electrodes are in the shape of "tips" fitted on the ends +of two short brass rods. + +A one-inch spark coil will give very good results by connecting the +spark-gap directly across the secondary of the coils. The aerial is +connected to one side of the gap and the ground to the other. + +The transmitter may be "tuned" and the range sometimes increased by +using a condenser and a helix. + +A condenser is most easily made by coating the inside and outside of a +test-tube with tinfoil so as to form a miniature Leyden jar. The end of +the tube is closed with a cork through which passes a brass rod +connecting to the inner coating of tinfoil. + +[Illustration: Fig. 223.—Diagram showing how to connect a Simple +Transmitter.] + +If such a condenser is connected directly across the spark-gap, the +spark will become very white and crackling. + +Several tubes may be arranged in a rack as shown in Figure 225. + +A helix consists of a spiral of brass ribbon set in a wooden frame. The +two strips composing the frame are each nine inches long. The spiral +consists of eight turns of brass ribbon, three-eighths of an inch wide, +set in saw-cuts made in the frame. A binding-post is connected to the +outside end of the ribbon. + +Figure 228 shows how to connect a helix and a condenser to a coil and a +spark-gap. + +The two clips are made by bending a strip of sheet brass and connecting +a piece of flexible wire to one end. + +[Illustration: Fig. 224.—A Test-Tube Leyden Jar.] + +In large stations, the best position for the clips is found by placing a +"hot-wire ammeter" in the aerial circuit and then moving the clips until +the meter shows the highest reading. + +The young experimenter will have to tune his set by moving the helix +clips about until the best results are obtained in sending. + +[Illustration: Fig. 225.—Eight Test-Tube Leyden Jars mounted in a Wooden +Rack.] + +If the spark coil is a good one and capable of giving a good hot spark, +it may be possible to tell when the set is in proper tune by placing a +small miniature tungsten lamp in series with the aerial and changing the +clips, the condenser, and the length of the spark-gap until the lamp +lights the brightest. + +An _oscillation transformer_ is sometimes used to replace an ordinary +helix when it is desirable to tune a station very closely so that its +messages shall not be liable to be confused with those of another +station when both are working at the same time. + +[Illustration: Fig. 226.—A Helix and Clip.] + +An oscillation transformer consists of two helixes arranged so that one +acts as a primary and the other as a secondary. An oscillation helix may +be made by making two sets of helix frames similar to that in Secondary +Figure 226. + +[Illustration: Fig. 227.—An Oscillation Transformer.] + +The primary should be provided with eight turns of brass ribbon and the +secondary with twelve. The primary supports a stiff brass rod upon which +the secondary is mounted. The secondary should slide up and down on the +rod but move very stiffly so that it will stay where it is put. + +[Illustration: AN OSCILLATION HELIX.] + +[Illustration: AN OSCILLATION CONDENSER.] + +An ordinary double-throw, double-pole knife switch having a porcelain +base will make a very good aerial switch in a small station. It is used +to connect the aerial and ground to either the transmitting or receiving +apparatus at will. Such a switch is shown in Figure 230. + +[Illustration: Fig 228.—Circuit showing how to connect a Helix and a +Condenser.] + +The aerial should be connected to the post _A_ and the ground to _B_. +The posts _E_ and _F_ lead to the transmitter, and _C_ and _D_ to the +receptor, or vice-versa according to which is the more convenient from +the location of the apparatus on the table or operating bench. + +A suitable table should be arranged to place the wireless instruments +upon so that they may be permanently connected together. + +[Illustration: Fig 229.—Circuit showing how to connect an Oscillation +Transformer and a Condenser.] + +The Continental Code is the one usually employed in wireless telegraphy. +It differs slightly from Morse as it contains no space letters. It will +be found easy to learn and somewhat easier to handle than Morse. + +[Illustration: Fig 230.—An Aerial Switch.] + +Two or three months’ steady practice with a chum should enable the young +experimenter to become a very fair wireless telegraph operator. Then by +listening for some of the high power wireless stations which send out +the press news to ships at sea during the evening it should be possible +to become very proficient. The press news is sent more slowly than +ordinary commercial wireless messages, and is therefore easy to read and +a good starting point for the beginner learning to read. + +[Illustration: Fig 231.—A Complete Wiring Diagram for both the +Transmitter and the Receptor.] + +[Illustration: Fig. 232.—The Continental Alphabet.] + +*A Coherer Outfit* + +*A Coherer Outfit* is usually capable of only receiving messages coming +from a distance of under one mile. In spite of this fact, however, it is +an exceedingly interesting apparatus to construct and experiment with, +and for this reason is found fully described below. + +A coherer set will ring a bell or work a sounder for short distances and +therefore is the best sort of an arrangement for demonstrating the +workings of your wireless apparatus to your friends. + +The first thing that you need for a coherer is a pair of double +binding-posts. Mount these about an inch and three-quarters apart on a +wooden base, six inches long and four inches wide as shown in Figure +233. + +[Illustration: Fig. 233.—A Coherer and a Decoherer.] + +Get a piece of glass tubing about an inch and one-half long and about +one-eighth of an inch inside diameter. You will also need some brass rod +which will just slide into the tube tightly. Cut off two pieces of the +brass rod each one and three-quarters inches long and slip these through +the upper holes in the binding-posts and into the glass tube as shown in +Figure 234. Before putting the second rod in place, however, you must +put some nickel and silver filings in the tube, so that when the rods +are pushed almost together, with only a distance of about one-sixteenth +of an inch between them, the filings will about half fill the space. + +The filings must be very carefully prepared, and in order to make them, +first use a coarse-grained file on the edge of a five-cent piece. Do not +use the fine dust and powder, but only the fairly coarse filings. Mix a +few silver filings from a ten-cent piece with the nickel in such +proportion that the mixture is 90% nickel and 10% silver. + +[Illustration: Fig. 234.—Details of the Coherer.] + +You will have to experiment considerably to find out just the right +amount of filings to place in the tube, and how far apart to place the +brass rods or plugs. + +Remove the gong from an old electric bell and mount the bell on the base +as shown in Figure 233. It should be in such a position that the bell +hammer will touch the coherer very lightly when the bell is ringing. + +The two binding-posts, tube rods, and filings constitute the _coherer_. +The bell is the _decoherer_. + +The next thing required in order to complete the apparatus is a relay. +You may use the relay described in Chapter X or build one according to +the plan shown in Figure 235. This relay consists of a single +electro-magnet mounted on a wooden base, two inches wide and four inches +long. The armature is a piece of soft iron rod one-quarter of an inch in +diameter and one-eighth of an inch long, riveted to the end of a thin +piece of spring brass, about No. 34 B. & S. gauge in thickness. + +[Illustration: Fig. 235.—The Relay.] + +The other end of the spring is fitted to a bracket and provided with a +thumbscrew to adjust the tension of the spring. + +The under side of the armature and the upper side of the magnet core are +each fitted with a small silver contact. + +The contacts should meet squarely when the armature is drawn down on to +the core by a current of electricity passing through the electro-magnet. + +By turning the adjusting screw, the armature can be raised or lowered. +It should be adjusted so that it almost touches the core and is only +just far enough away to slip a piece of thick paper under. + +The terminals of the magnet are connected to the two binding-posts on +the base marked _S_ and _S_. One of the binding-posts, _P_, is connected +to the brass upright, and the other is connected to the core of the +magnet. + +Figure 236 shows how to connect up the outfit. It will require some very +nice adjusting before you will be able to get it to working properly. + +[Illustration: Fig. 236.—The Complete Coherer Outfit.] + +If you wish to use the outfit for demonstration purposes or for sending +messages for very short distances, as for instance across a room, you do +not need an aerial but merely a pair of "catch-wires." + +The "catch-wires" are two pieces of stiff copper wire, about two feet +long, placed in the lower holes in the double binding-posts forming part +of the coherer. + +In order to set the apparatus for operation, raise the adjusting screw +of the relay until the armature is quite far away from the core. Then +push the armature down against the contact on the core. The decoherer +should then immediately operate and begin to tap the coherer. Then turn +the thumbscrew until the armature is brought down to the core in such a +position that it is as close as it is possible to get it without ringing +the bell. + +The transmitter should consist of a spark coil, battery, key, and a +spark-gap. The gap should be connected to the secondary of the coil and +adjusted so that the electrodes are only about one-eighth of an inch +apart. The key is placed in series with the primary of the coil and the +battery, so that pressing the key will send a stream of sparks across +the gap. Fit the spark-gap with two catch-wires similar to those on the +coherer and place the transmitter about four or five feet away from the +coherer outfit. + +You are now likely to find that if you press the key of the transmitter, +the decoherer will ring. It is possible that it will continue to ring +after you have stopped pressing the key. If such is the case, it will be +necessary to turn the adjusting screw on the relay so as to move the +armature upward a short distance away from the core. + +If the decoherer will not operate each time when you press the key, the +brass plugs in the coherer need adjusting. You must not be discouraged +if you have some difficulty in making the apparatus work at first. After +you learn how to adjust it properly, you will find that you can move the +transmitter quite a distance away from the coherer and it will still +operate very nicely. + +After you manage that, you can place the apparatus in separate rooms and +find it possible to work it just the same, because ordinary walls will +not make any difference to wireless waves. + +Bear in mind that the nearer the coherer plugs are to each other, the +more sensitive the coherer will be, but that if too close, the decoherer +will not be able to shake the filings properly and will not stop when +you stop pressing the key. + +The operation of the apparatus depends upon the fact that when properly +adjusted the resistance of the filings between the two brass plugs is +too great to allow sufficient battery current to flow to attract the +armature of the relay. As soon as any wireless waves from the +transmitter strike the catch-wires of the coherer, they cause the +filings to cling together or cohere. When in this state, they have a low +resistance and permit the current to flow in the relay circuit and draw +down the armature. The armature closes the second circuit and sets the +decoherer into operation. The decoherer shakes the filings and causes +them to decohere or fall apart and so makes them ready again for the +next signal. + +A coherer set of this sort may be used on an aerial and ground by +substituting the coherer for the detector, but otherwise following any +of the receiving circuits which have already been shown. + + + +CHAPTER XV A WIRELESS TELEPHONE + + +Probably many readers of the "Boy Electrician" are amateur wireless +operators and have constructed their own apparatus with which they are +able to pick up commercial messages or communicate with other +experimenters in the neighborhood, but not many have ever built a +wireless telephone. + +The device described in the following pages is easy to make and arrange, +and will serve for some very interesting experiments. + +It is of no practical value as a commercial wireless telephone, because +the distance over which it will transmit speech is limited to from 250 +to 300 feet. If you have a chum who lives across the street and within +the distance named above, it is possible for you to construct a simple +wireless telephone which will enable you to remain in your own rooms and +talk to each other without any connecting wires. + +The instruments operate by magnetic induction. It has already been +explained how it is possible for the current in the primary of an +induction coil to induce a current in the secondary coil, even though +the two are not electrically connected. This type of wireless telephone +really consists of an induction coil in which the two windings are +widely separated. + +Suppose that two coils of wire are connected as in Figure 237. The +illustration shows that one coil, _A_, is connected in series with a set +of batteries and a telegraph key. The terminals of the other coil, _B_, +are connected to a telephone receiver. The coils are placed parallel to +each other and a few inches apart. If the key is pressed so that the +battery current may flow through the coil, _A_, it will create a +magnetic field, and lines of force will be set up in the immediate +vicinity. The lines of force will pass through the coil, _B_, and induce +in it a current of electricity which will cause a sound like a click to +be heard in the telephone receiver. + +[Illustration: Fig. 237.—A Simple Arrangement showing the Inductive +Action between two Coils.] + +If a telephone transmitter is substituted for the key and words are +spoken into it, the current passing through the coil from the battery +will vary with each vibration of the voice and the words will be +distinctly repeated by the receiver connected to _B_. + +This experiment may be tried by any boy with the equipment he probably +has already around his shop. Twenty-five to thirty turns of wire wound +around a cardboard tube five or six inches in diameter will serve as a +coil. Two such coils, an ordinary telephone transmitter, a telephone +receiver and a couple of dry cells are all that is required. + +[Illustration: Fig. 238.—A Simple Wireless Telephone. Speech directed +into the Transmitter can be heard in the Receiver, although there is no +direct electrical connection between the two.] + +The diagram in the accompanying illustration shows how the apparatus is +arranged. The coils may be used several inches apart and the voice will +be clearly heard in the receiver. + +Such an outfit is, however, only experimental, and if it is desired to +make a practical set, the coils, etc., must be much larger in diameter +and contain a greater number of turns. + +Larger coils are made by first drawing a circle four feet in diameter on +the floor of the "shop" or attic. Then drive a number of small nails +around the circumference, about four inches apart. + +Procure two and one-half pounds of No. 20 B. & S. gauge cotton-covered +magnet wire and wind it around the circumference of the circle. The wire +should form at least sixty complete turns. About one foot should be left +at each end to establish connections with. After winding, the coil +should be tied about every six inches with a small piece of string so +that it will retain its shape and not come apart. The nails are then +pulled out so that the coil may be removed. + +The coil may be used just as it is for experimental purposes, but if it +is intended for any amount of handling it is wise to procure a large +hoop such as girls use for rolling along the sidewalk, and make the coil +the same diameter as the hoop so that upon completion they may be firmly +bound together with some insulating tape. Two binding-posts may then be +fastened to the hoop and the terminals of the coil connected to them. + +Two such coils are required for a complete wireless telephone system, +one to be located at each station. + +It is also necessary to make a double-contact strap-key. Such a key is +easily built out of a few screws and some sheet-brass. The illustration +shows the various parts and construction so clearly that no detailed +explanation is necessary. + +[Illustration: Fig. 239.—A Double-Contact Strap-Key. The Dotted Lines +show how the Binding-Posts are connected.] + +The telephone transmitter and the telephone receiver required for this +experiment must be very sensitive, and it is hardly possible for the +young experimenter to build one which will be satisfactory. They can be +secured from a second-hand telephone or purchased at an electrical +supply house. The transmitter should be of the "long distance" type. An +80-ohm receiver will serve the purpose, but if you also have a wireless +station, use the same 1000-ohm receivers belonging to your wireless set +and you will secure very good results. + +A battery capable of delivering about 10 volts and a good constant +current is required. + +The apparatus is connected as shown in Figure 240. + +When the key is pressed, the coil is connected to the battery and the +telephone transmitter. If words are then spoken into the transmitter +they will vary the amount of current flowing and the magnetic field +which is set up in the neighborhood of the coil will induce currents in +the coil at the other station, provided that it is not too far away, and +cause the words to be reproduced in the telephone receiver. + +When the key is released it will connect with the upper contact and +place the telephone receiver in the circuit for receiving, so that your +chum at the other station can answer your message by pressing his key +and talking into his transmitter. + +[Illustration: Fig. 240.—The Circuit of the Wireless Telephone. When the +Key is up, the Receiver is ready for Action. When the Key is pressed, +the Transmitter and Battery are thrown into the Circuit.] + +The best plan is to mount each of the coils upon a tripod and experiment +by placing them close together at first and gradually moving them apart +until the maximum distance that the apparatus will work is discovered. + +Be very careful to keep the two coils exactly parallel. + +Much depends upon the battery. Be certain that it is capable of +delivering a good strong current. Do not hold the key down any longer +than is absolutely necessary, or the telephone transmitter will become +hot. + +By making the coils six feet in diameter and placing from 200 to 400 +turns of wire in each coil you can make a set which is capable of +transmitting speech 300 feet or more. + +[Illustration: Fig. 241.—A Complete Wireless Telephone and Telegraph +Station for Amateurs. 1. The Telephone Coil. 2. The Telephone +Transmitter. 3. Double-Contact Strap-Key. 4. The Battery. 5. Spark Coil. +6. Key. 7. Spark-Gap. 8. Aerial Switch. 9. Loose Coupler. 10. Detector, +11. Fixed Condenser. 12. Code Chart. 13. Amateur License. 14. Aerial. +15. Telephone Receivers.] + +The coil may be mounted on the wall of your shop in a position where it +will be parallel to one located in your chum’s house. + +The success of a wireless telephone system of this sort lies in making +the coils of large diameter and many turns, in keeping the coils +parallel, using a sensitive transmitter and receiver, and in employing a +good strong battery. Storage cells are the best for the purpose. + + + +CHAPTER XVI ELECTRIC MOTORS + + +The first American patentee and builder of an electric motor was Thomas +Davenport. The father of Davenport died when his son was only ten years +old. This resulted in the young inventor being apprenticed to the +blacksmith’s trade at the age of fourteen. + +Some years later, after having thoroughly learned his trade, he married +a beautiful girl of seventeen, named Emily Goss, and settled in the town +of Brandon, Vermont, as an independent working blacksmith. + +About this time Joseph Henry invented the electro-magnet. Davenport +heard of this wonderful "galvanic magnet" which it was rumored would +lift a blacksmith’s anvil. This was his undoing, for never again was he +to know peace of mind but was destined to always be a seeker after some +elusive scientific "will-o’-the-wisp." Although many times he needed +iron for his shop, the greater part of his money was spent in making +electro-magnets and batteries. + +In those days insulated wire could not be purchased, and any one wishing +insulated wire had to buy bare wire and insulate it himself. It was then +supposed by scientists that silk was the only suitable material for +insulating wire and so Davenport’s brave young wife cut her silk wedding +gown into narrow strips and with them wound the coils of the first +electric motor. + +Continuing his experiments in spite of almost insurmountable +difficulties and making many sacrifices which were equally shared by his +family, he was enabled to make a trip to Washington in 1835 for the +purpose of taking out a patent. His errand was fruitless, however, and +he was obliged to return home penniless. + +Nothing daunted, he made the second and third trip and finally secured +his memorable patent, the first of the long line of electric-motor +patents that have made possible both the electric locomotive that hauls +its long train so swiftly and silently, and the whirring little fan +which stirs up a breeze during the hot and sultry days. + +These are a few of the reasons why a modest country blacksmith, in turn +an inventor and an editor, through perseverance in struggling against +adversity and poverty succeeded in placing his name on the list which +will be deservedly immortal among the scientists and engineers of the +world. + +*A Simple Electric Motor* can be made in fifteen minutes by following +the plan shown in Figure 242. + +The armature is made by sticking a pin in each end of a long cork. The +pins should be as nearly central as it is possible to make them, so that +when the cork is revolved upon them it will not wabble. The pins form +the shaft or spindle of the motor. Then take about ten feet of fine +magnet wire (Nos. 28-32 B. & S. gauge) and wind it on as shown in the +illustration, winding an equal number of turns on each side of the two +pins. + +[Illustration: Fig. 242.—A Simple Electric Motor which may be made in +Fifteen Minutes.] + +When this is finished, fasten the wire securely to the cork by binding +it with thread. + +Bend the two free ends (the starting and the finishing end) down at +right angles and parallel to the shaft so as to form two commutator +sections as shown in the upper left hand corner of Figure 242. Cut them +off so that they only project about three-eighths of an inch. Bare the +ends of the wire and clean them with a piece of fine emery paper or +sandpaper. + +The bearings are made by driving two pins into a couple of corks so that +the pins cross each other as shown in the upper right-hand corner of +Figure 242. + +They must not be at too sharp an angle, or when the armature is placed +in position, the friction of the shaft will be so great that it may not +revolve. + +The motor is assembled by placing the armature in the bearings and then +mounting two bar magnets on either side of the armature. The magnets may +be laid on small blocks of wood and should be so close to the armature +that the latter just clears when it is spun around by hand. The north +pole of one magnet should be next to the armature and the south pole of +the other, opposite. + +Connect two wires about one foot long and No. 26 B. & S. gauge in +diameter to a dry cell. Bare the ends of the wires for about an inch and +one half. + +Take the ends of the two wires between the forefinger and thumb and bend +them out, so that when the armature is revolved they can be made just to +touch the ends of the wire on the armature, or the "commutator +sections," as they are marked in the drawing. + +Give the armature a twist so as to start it spinning, and hold the long +wires in the hand so that they make contact with the commutator as it +revolves. + +Very light pressure should be used. If you press too hard, you will +prevent the armature from revolving, while, on the other hand, if you do +not press hard enough, the wires will not make good contact. + +The armature will run in only one direction, and so try both ways. If +you start it in the right direction and hold the wires properly, it will +continue to revolve at a high rate of speed. + +If carefully made, this little motor will reward its maker by running +very nicely. Although it is of the utmost simplicity it demonstrates the +same fundamental principles which are employed in real electric motors. + +*The Simplex Motor* is an interesting little toy which can be made in a +couple of hours, and when finished it will make an instructive model. + +[Illustration: Fig. 243.—Details of the Armature of the Simplex Motor.] + +As a motor itself, it is not very efficient, for the amount of iron used +in its construction is necessarily small. The advantage of this +particular type of motor and the method of making it is that it +demonstrates the actual principle and the method of application that is +used in larger machines. + +The field of the motor is of the type known as the "simplex" while the +armature is the "Siemens H" or two-pole type. The field and the armature +are cut from ordinary tin-plated iron such as is used in the manufacture +of tin cans and cracker-boxes. + +The simplest method of securing good flat material is to get some old +scrap from a plumbing shop. An old cocoa tin or baking-powder can may, +however, be cut up and flattened and will then serve the purpose almost +as well. + +[Illustration: Fig. 244.—The Armature.] + +*The Armature.* Two strips of tin, three-eighths of an inch by one and +one-half inches, are cut to form the armature. They are slightly longer +than will actually be necessary, but are cut to length after the finish +of the bending operations. Mark a line carefully across the center of +each strip. Then, taking care to keep the shape symmetrical so that both +pieces are exactly alike, bend them into the shape shown in Figure 243. +The small bend in the center is most easily made by bending the strip +over a knitting-needle and then bending it back to the required extent. + +[Illustration: Fig. 245.—The Field.] + +A piece of knitting-needle one and one-half inches long is required for +the shaft. Bind the two halves of the armature together in the position +shown in Figure 249. Bind them with a piece of iron wire and solder them +together. The wire should be removed after they are soldered. + +[Illustration: Fig. 246.—The Field and Commutator.] + +*The Field Magnet* is made by first cutting out a strip of tin one-half +by four and then bending it into the shape shown in Figure 245. + +The easiest way of doing this with accuracy is to cut out a piece of +wood as a form, and bend the tin over the form. The dimensions shown in +Figure 245 should be used as a guide for the form. + +[Illustration: Fig. 247.—The Bearings.] + +Two small holes should be bored in the feet of the field magnet to +receive No. 3 wood screws, which fasten the field to the base. + +*The Bearings* are shown in detail in Figure 247. They are easily made +by cutting from sheet-tin. Two small washers, serving as collars, should +be soldered to the shaft as shown in Figure 243. + +*The Commutator Core* is formed by cutting a strip of paper +five-sixteenths of an inch wide and about five inches long. It should be +given a coat of shellac on one side and allowed to get sticky. The strip +is then wrapped around the shaft until its diameter is three-sixteenths +of an inch. + +*The Base* is cut from any ordinary piece of wood and is in the form of +a block about two by one and one-half by one-half inch. + +[Illustration: Fig. 248.—The Complete Motor.] + +*Assembling the Motor.* The parts must be carefully prepared for winding +by covering with paper. Cut a strip of paper one-half inch wide and one +and one-eighth of an inch long and give it a coat of shellac on one +side. As soon as it becomes sticky, wrap it around the top bar of the +field magnet. The armature is insulated in exactly the same way, taking +care that the paper covers the entire flat portion. + +The field and armature are now ready for winding. It is necessary to +take proper precautions to prevent the first turn from slipping out of +place. + +This is accomplished by looping a small piece of tape or cord over it. +The next two turns are then taken over the ends of the loop so as to +embed them. Wind on three layers of wire and when in the middle of the +fourth layer embed the ends of another loop, which may be used at the +end of the fourth layer to fasten the end so that it will not unwind. +After the winding is finished, give it a coat of shellac. + +The winding of the armature is somewhat more difficult. + +The wire used for winding both the armature and the field should be No. +25 or No. 26 B. & S. gauge double-cotton-covered. + +In order to wind the armature, cut off about five feet of wire and +double it back to find the center. Then place the wire diagonally across +the center of the armature so that there is an equal length on both +sides. Place a piece of paper under the wire at the crossing point to +insulate it. Then, using one end of the wire, wind four layers on half +of the armature. Tie the end down with a piece of thread and wind on the +other half. + +The ends of the wire are cut and scraped to form the commutator +segments. Figure 246 shows how this is done. + +Bend the wires as shown so that they will fit closely to the paper core. +Bind them tightly into position with some silk thread. Use care so that +the two wires do not touch each other. Cut the free ends of the wires +off close to the core. + +When finished, the relative positions of the armature and the commutator +should be as shown in Figure 248. + +The brushes are made by flattening a piece of wire by a few light hammer +blows. + +The brushes are fastened under a small clamp formed by a strip of tin +held down at each end with a wood screw. They can be adjusted to the +best advantage only under actual working conditions when the current is +passing through the motor. One or two dry cells should be sufficient to +operate the motor. + +[Illustration: Fig. 249.—Details of the Motor.] + +One end of the field winding is connected to one of the brushes. The +other brush and the other end of the field form the terminals to which +the battery is connected. + +The motor, being of the two-pole armature type, must be started when the +current is turned on by giving it a twist with the fingers. + +*A Larger Motor* may be built in somewhat the same manner as the one +just described by cutting armature and field out of sheet tin. It will +be more substantial if it is built up out of laminations and not bent +into shape, as in the case of the other. + +Lay out an armature disk and a field lamination on a sheet of tin in +accordance with the dimensions and pattern shown in Figure 249. These +pieces are used as patterns for laying out the rest of the laminations. + +[Illustration: Fig. 250.—Complete Motor.] + +Place them on some thin sheet-iron and trace the outline with a +sharp-pointed needle. Then cut a sufficient number of pieces of each +pattern to form a pile three-quarters of an inch thick. + +Four laminations for the field should be cut with extensions shown by +the dotted lines. They are bent out at right angles for mounting the +motor and holding it upright. + +Assemble the armature and field by piling the pieces on top of each +other and truing them up. Enough laminations should be used to form a +pile three-quarters of an inch thick when piled up and clamped tightly. + +File off any burrs and rough edges and then bind the laminations +together with some string to hold them until wound. + +Wrap a couple of layers of paper around those portions of the armature +and field which are liable to come into contact with the iron. Five or +six layers of No. 18 B. & S. gauge double-cotton-covered magnet wire are +sufficient to form the field coil. + +The armature is wound with three or four layers of wire of the same +size. + +The commutator is made out of a circular piece of hard wood or fiber, +fitted with segments cut out of thin sheet-copper. The segments may be +fastened to the core with thick shellac or some melted sealing-wax. The +ends may be bound down tightly by wrapping with silk thread. + +The brushes are cut out of thin sheet-copper similar to that used for +the commutator segments. + +The bearings are strips of heavy sheet-brass bent into the shape shown. +They are mounted by passing a nail through the holes in the ends and +through the holes, A and B, in the field and then riveting the ends +over. + +Assemble the motor as shown in Figure 255. If desirable, a small pulley +may be fitted to the shaft and the motor used to run small mechanical +toys. If it is properly constructed, two or three dry cells will furnish +sufficient current to run the motor at high speed. + + + +CHAPTER XVII DYNAMOS + + +There is perhaps no other electrical device entering into the young +experimenter’s domain requiring the careful workmanship and tool +facilities that the dynamo does. In order to construct a practical +working dynamo it would be necessary to have at hand a lathe for turning +the castings. + +Rather than describe a machine which comparatively few of my readers +would be able to build, I have explained below how it is possible to so +alter an old telephone magneto that it may be made to serve as a small +dynamo. Telephone magnetos, also sometimes called hand generators, are +used in many telephone systems to supply the current which rings the +telephone bell at the other end. The magneto is placed in a small box on +the telephone, only the handle being exposed. In order to make a call +the handle is given several brisk turns before raising the receiver. +When the handle is turned the moving parts of the generator revolve and +produce a current of electricity which goes forth over the line and +rings the bell at the other end. + +[Illustration: Fig. 251—A Telephone Magneto.] + +Telephone magnetos are gradually being discarded in all the large +telephone systems, a method known as "central energy," in which the +current for ringing bells is supplied from the central office, taking +their place. For that reason, there are a great many telephone magnetos +to be found in second-hand shops and at electrical houses, where they +can be purchased for a fractional part of the original cost. Fifty cents +will buy a first-class second-hand telephone magneto. The author saw a +pile of telephones as large as a haystack, each telephone containing a +magneto, in the back yard of a second-hand shop, and the owner would +have been glad to sell the complete instruments for fifty cents each. + +Before explaining how to reconstruct such a machine, it is best to +impress upon the reader that a careful study of the principles of the +dynamo is well worth the time spent. + +Almost any book on physics or electricity, or even the encyclopedia, +will be found to contain a description of this wonderful machine that +supplies the power for running the trolley cars, electric lights, etc., +in fact all of the electricity in use to-day with the exception of that +generated by batteries for telegraph and telephone lines. + +It will be remembered that if a bar magnet is suddenly plunged into a +hollow coil of wire, a momentary electric current will be generated in +the coil. The current is easily detected by means of an instrument +called a galvanometer. The space in the vicinity of a magnet is filled +with a peculiar invisible force called magnetism. The magnetism flows +along a certain path, passing through the magnet itself and then +spreading out in curved lines. If a sheet of paper is laid over a magnet +and a few iron filings are sprinkled on the paper, they will follow the +magnetic lines of force. + +When the magnet is plunged into the hollow coil, the lines of force flow +through the turns of wire, or are said to cut them. Whenever lines of +force cut a coil of wire and they are in motion, electricity is +produced. It does not matter whether the coil is slipped over the magnet +or the magnet is plunged into the coil, a current will be produced as +long as they are in motion. As soon as the magnet or the coil stops +moving the current stops. + +By arranging a coil of wire between the poles of a horse-shoe magnet so +that it can be made to revolve, the motion can be made continuous and +the current of electricity maintained. + +Figure 252 shows such an arrangement. Some means of connection with the +coil of wire must be established so that the current can be led off. If +two metal rings are connected to the ends of the coil, connection can be +made by little strips of metal called brushes rubbing against the rings. +This scheme is the principle of the telephone magneto and the basis of +all dynamos. + +[Illustration: Fig. 252.—The Principle of the Alternator and the +Direct-Current Dynamo.] + +In the telephone magneto, more than one horseshoe magnet is usually +provided. The coil of wire revolves between the poles of the magnets. +The coil is wound around an iron frame and together they are called the +armature. The end of the armature shaft is fitted with a small spur gear +meshing with a larger gear bearing a crank, so that when the crank is +turned the motion is multiplied and the armature is caused to revolve +rapidly. One end of the coil or armature winding is connected to a small +brass pin. This pin connects with a second pin set in the end of the +shaft in an insulating brush of hard rubber. The other terminal of the +coil is connected to the armature itself. Thus connection can be had to +the coil by connecting a wire to the frame of the machine and to the +insulated pin. + +[Illustration: Fig. 253.—Details of the Armature, Commutator, and +Brushes.] + +The armature of a magneto is usually wound with a very fine silk +insulated wire, about No. 36 B. & S. gauge in size. This should be +carefully removed and wound upon a spool for future use. Replace the +wire with some ordinary cotton-covered magnet wire, about No. 24 or 25 +B. & S. gauge, winding it on very carefully and smoothly. Connect one +end of the winding to the pin leading to the insulated pin by soldering +it. This pin is the one at the end of the shaft opposite to that one to +which the spur gear is fastened. Connect the other end of the wire to +the pin at the same end of the shaft as the gear. This pin is grounded, +that is, connected to the frame. + +An ordinary telephone magneto gives a very high voltage current. The +voltage may vary from twenty-five to several hundred, depending upon how +fast the machine is run. This is due to the fact that the armature +winding is composed of a very large number of turns of wire. The more +turns that are placed on the armature, the higher its voltage will be. +The current or amperage of a large telephone magneto wound with a large +number of turns of fine wire is very low. Too low in fact to be used for +anything except ringing a bell or testing. Winding the armature with +fewer turns of large wire reduces the voltage and increases the amperage +so that the current will light a small lamp or may be used for other +purposes. The winding does not change the principle of the magneto, it +merely changes its amperage and voltage. + +The magneto may be mounted on a wooden base-board and screwed to a +table, so that the handle may be turned without inconvenience. A small +strip of copper, called a brush, should be fastened to the base with a +screw and brought to bear against the end of the insulated pin. The +brush should be connected to a binding-post with a piece of wire. A +second wire leading to a binding-post should be connected to the frame +of the magneto. When the handle is turned rapidly, currents may be drawn +from the two binding-posts. + +The current is of the kind known as alternating, that is to say, it +flows first in one direction, then reverses and flows in the other. + +In order to make the machine give direct current, it must be fitted with +a commutator. This is somewhat difficult with some magnetos but the +following plan may be carried out in most cases. Cut a small fiber +circle or disk about one inch in diameter from sheet fiber +three-sixteenths of an inch thick. Cut a small hole in the center, just +large enough so that the fiber will slip very lightly over the end of +the shaft from which the insulated pin projects. Two small commutator +sections similar to that shown in Figure 253 must be cut from +sheet-brass or sheet-copper. The three long ears shown in the drawing +are bent back around the fiber and squeezed down flat with a pair of +pincers so that they grip the fiber very tightly and will not slip. One +ear on one section should be bent over the back down to the hole, where +it will connect with the shaft. The other section of the commutator is +connected to the insulated pin by a drop of solder. In this manner, one +end of the winding is connected to one section of the commutator and the +other end to the other section. The commutator should fit tightly on the +end of the shaft so that it will not twist. The dividing line between +the section should be parallel to a line drawn to the axis of the actual +armature coil. When the iron parts of the armature are nearest the poles +of the horseshoe magnets in their revolution, the slot in the commutator +should be horizontal. + +When the magnet is provided with a commutator, it may also be run as a +motor by connecting it to a battery. In order to operate it either as a +dynamo or a motor, however, it must first be fitted with a pair of +brushes. They are shown in detail in Figure 253. They are made from two +small strips of sheet-copper bent as shown and mounted on a small wooden +block. They must be adjusted to bear against the commutator so that when +the dividing line between the two sections is horizontal, the upper +brush bears against the upper section and the lower brush against the +lower section. The two brushes form the terminals of the machine. They +should be connected to binding-posts. + +[Illustration: Fig. 254.—The Complete Generator.] + +In order to operate the dynamo properly and obtain sufficient current +from it to operate a couple of small incandescent lamps, it will have to +be provided with a pulley mounted on the end of the shaft after the gear +wheel has been removed. The dynamo may then be driven at high speed by +connecting it to a sewing-machine with a belt, or the back wheel of a +bicycle from which the tire has been removed. + +The completed dynamo is shown in Figure 254. The voltage and amperage of +the dynamo will depend upon the machine in question, not only upon the +size of the wire but also upon the size of the machine, the speed at +which it is run, and the strength of the horseshoe magnets. It is +impossible to tell just what the current will be until it is tested and +tried. + + +A 10-Watt Dynamo + + +Probably few experimenters fully understand how almost impossible it is +to construct a dynamo, worthy of the name as such, without resort to +materials and methods employed in the commercial manufacture of such +machines. Practical telegraph instruments, telephones, etc., can be +constructed out of all sorts of odds and ends, but in order to make a +real dynamo it is necessary to use certain materials for which nothing +can be substituted. + +_The field magnets_ must be soft gray cast-iron except in special +instances. + +_The wire_ used throughout must be of good quality and must be new. + +The necessity for good workmanship in even the smallest detail cannot be +overestimated. Poor workmanship always results in inefficient working. +No dynamo will give its stated output continuously and safely unless the +materials and workmanship are up to a high standard. + +Since castings must be used as field magnets, a pattern is necessary to +form the mould for the casting. Pattern work is something requiring +skill and knowledge usually beyond the average experimenter. A lathe is +necessary in order to bore or tunnel the space between the ends of the +field magnet into which the armature fits. + +It may be possible for several boys to club together and have a pattern +made by a pattern-maker for building a dynamo. Then by using the lathe +in some convenient shop or manual training school secure a field magnet +and armature for a really practical small dynamo. + +[Illustration: Fig. 255.—Details of the Field Casting.] + +For these reasons, I have described below a small dynamo of about ten +watts output, the castings for which can be purchased from many +electrical dealers with all machine work done at an extremely low price. + +The field magnet shown in Figure 255 is drawn to scale and represents +the best proportions for a small "overtype" dynamo of ten to fifteen’ +watts output. + +The dimensions are so clearly shown by the drawings that further comment +in that respect is unnecessary. + +The armature is of the type known as the "Siemen’s H." It is the +simplest type of armature it is possible to make, which is a feature of +prime importance to the beginner at dynamo construction, although it is +not the most efficient form from the electrical standpoint. The armature +in this case is also a casting and therefore a pattern is required. + +[Illustration: Fig. 256.—Details of the Armature Casting.] + +The patterns for both the field and the armature are of the same size +and shape as shown in Figures 255 and 256. They are made of wood, and +are finished by rubbing with fine sandpaper until perfectly smooth and +then given a coat of shellac. The parts are also given a slight "draft," +that is, a taper toward one side, so that the pattern may be withdrawn +from the mould. + +The patterns are turned over to a foundry, where they are carefully +packed in a box, called a "flask," full of moulder’s sand. When the +patterns are properly withdrawn, they will leave a perfect impression of +themselves behind in the sand. The mould is then closed up and poured +full of molten iron. When the iron has cooled the castings are finished +except for cleaning and boring. + +The shaft is a piece of steel rod, three-sixteenths of an inch in +diameter, and four and one-half inches in length. + +The portion of the field into which the armature fits is bored out to a +diameter of one and five-sixteenth inches. Considerable care is +necessary in performing this operation in order not to break the field +magnet apart by taking too heavy a cut. + +[Illustration: Fig. 257.—Details of the Commutator.] + +The armature should be turned down to a diameter of one and one-quarter +inches or one-sixteenth of an inch smaller than the tunnel in which it +revolves between the field magnets. The center of the armature is bored +out to fit the shaft. + +Figure 257 shows a two-part commutator for fitting to an armature of the +"Siemen’s H" type. It consists of a short piece of brass tubing fitted +on a fiber core and split length-wise on two opposite sides, so that +each part is insulated from the other. + +The fiber is drilled with a hole to fit tightly on the shaft. It is then +placed in a lathe and turned down until a suitable piece of brass tube +can be driven on easily. + +Two lines are then marked along the tube diametrically opposite. A short +distance away from each of these lines, and on each side of them, bore +two small holes to receive very small wood screws. The screws should be +counter-sunk. It is very important that none of the screws should go +into the fiber core far enough to touch the shaft. + +The commutator may then be split along each of the lines between the +screws with a hacksaw. The saw-cut should be continued right through the +brass and slightly into the insulating core. The space between the +sections of the commutator should be fitted with well-fitting slips of +fiber, glued in. + +The commutator should now be trued up and made perfectly smooth. + +[Illustration: Fig. 258.—Diagram showing how to connect the Armature +Winding to the Commutator.] + +The commutator is provided with a small brass machine screw threaded +into each section near the edge as shown in Figure 257. These screws are +to receive the ends of the armature winding and so facilitate +connections. + +The commutator, shaft and armature are assembled as shown in Figure 258. + +The armature may be held to the shaft by a small set screw or a pin. The +commutator should fit on the shaft very tightly so that it will not slip +or twist. + +Every part of the armature and shaft touched by the armature winding +must be insulated with paper which has been soaked in shellac until +soft. The armature must be left to dry before winding. + +The armature should next be wound with No. 20 B. & S. gauge +single-cotton-covered magnet wire. Sufficient wire should be put on to +fill up the winding space completely. Care should be taken, however, not +to put on too much wire or it will interfere with the field magnets and +the armature cannot revolve. After winding the armature, test it +carefully to see that the wire is thoroughly insulated from the iron. + +[Illustration: Fig. 259.—Details of the Wooden Base.] + +If the insulation is correct, paint the whole armature with thick +shellac varnish and bake it in a warm oven to set the shellac. + +Figure 258 is a diagram showing how the winding is made and connected. +It is wound about the armature, always in the same direction, just as if +the armature were an ordinary electro-magnet. + +The ends of the winding are each connected to one of the commutator +sections by scraping the wire and placing it under the screws. + +The winding space in the field magnet should be shellacked, and +insulated with brown paper by wrapping the core with a strip of paper +and covering the bobbin ends with circular pieces made in two halves. + +The field magnet is wound full of No. 20 B. & S. gauge +single-cotton-covered wire. The wire should be put on in smooth, even +layers and the winding space completely filled up. + +[Illustration: Fig. 260.—The Pulley and Bearings.] + +The base for the dynamo is a piece of hard wood, five inches long, four +inches wide, and five-eighths of an inch thick. + +The bearings are small brass castings of the dimensions shown in Figure +260. It is necessary first to make a wooden pattern and send it to the +foundry for the castings. + +The bearings are fastened to the projecting arms on the field casting by +means of machine screws eight-thirty-seconds of an inch in thickness. + +The field magnet should not be screwed down on to the base until the +armature runs easily and truly in the tunnel. + +The brushes are made from thin gauge sheet-copper according to the shape +and dimensions shown in Figure 261. + +They are bent at right angles and mounted on the base on either side of +the commutator with small round-headed wood screws. + +The completed dynamo is shown in Figure 262. One end of the shaft is +provided with a small pulley to accommodate a small leather belt. + +[Illustration: Fig. 261.—The Brushes.] + +The dynamo is connected as a "shunt" machine, that is, one terminal of +the field magnet is connected to one of the brushes, and the other +terminal to the other brush. + +A wire is then led from each of the brushes to a binding-post. + +A shunt dynamo will only generate when run in a certain direction. In +order to make it generate when run in the opposite direction, it is +necessary to reverse the field connections. + +The dynamo just described should have an output of from 10 to 15 watts +and deliver about 6 volts and 1 3/4 to 2 1/2 amperes. + +In order to secure current from the dynamo it will first be necessary to +magnetize the field by connecting it to several batteries. + +[Illustration: THE JUNIOR DYNAMO MOUNTED ON A LONG WOODEN BASE AND +BELTED TO A GROOVED WHEEL FITTED WITH A CRANK SO THAT THE DYNAMO CAN BE +RUN AT HIGH SPEED BY HAND POWER. THE ILLUSTRATION ALSO SHOWS A SMALL +INCANDESCENT LAMP CONNECTED TO THE DYNAMO SO THAT WHEN THE CRANK IS +TURNED THE LAMP WILL LIGHT.] + +It will be found that the dynamo will also operate as a very efficient +little motor, but that on account of having a two-pole armature it must +be started by giving the shaft a twist. + +[Illustration: Fig. 262.—Complete Dynamo.] + +It can be used as a generator for lighting small lamps, electro-plating, +etc., but cannot be used for recharging storage cells on account of +having a two-pole armature. + +The dynamo may be driven with a small water motor or from the +driving-wheel of a sewing-machine. + +Before the machine will generate as a dynamo, it must be connected to a +battery and run as a motor. This will give the field the "residual +magnetism" which is necessary before it can produce current itself. + + + +CHAPTER XVIII AN ELECTRIC RAILWAY + + +No toys loom up before the mind of the average boy with more appeal to +his love of adventure than do railway cars and trains. In England, the +construction and operation of miniature railways is the hobby not only +of boys but of grown men, and on a scale that is hardly appreciated in +this country. + +The height of ambition of many boys is not only to own a miniature +railway system but to build one. For some unknown reason, none of the +boys’ papers or books have heretofore given any information on this +interesting subject. The car shown in Figure 263 is such that it can be +easily built by any boy willing to exercise the necessary care and +patience in its construction. + +The first operation is to cut out the floor of the car. This is a +rectangular piece of hard wood, eight inches long, three and one-quarter +inches wide and one-half of an inch thick. Its exact shape and +dimensions are shown in Figure 264. + +The rectangular hole cut in the floor permits the belt which drives the +wheels to pass down from the counter-shaft to the axle. + +[Illustration: Fig. 263.—Complete Electric Railway operated by Dry +Cells. Note how the Wires from the Battery are connected to the Rails by +means of the Wooden Conductors illustrated in Figure 277.] + +The two pieces forming the wheel-bearings are cut out of sheet-brass +according to the shape and dimensions shown in Figure 265. The brass +should be one-sixteenth of an inch thick. The two projecting pieces at +the top are bent over at right angles so that they can be mounted on the +under side of the car floor by small screws passing through the holes. +The holes which form the bearings for the ends of the axles upon which +the wheels are mounted should be three inches apart. The bearings cannot +be placed in position on the under side of the car floor until the +wheels and axles are ready, but when this work is done, care should be +taken to see that they line up and come exactly opposite to each other. + +[Illustration: Fig. 264.—Details of the Floor of the Car.] + +The wheels themselves cannot be made by the young experimenter unless he +has a lathe. They are flanged wheels, one and one-eighth inches in +diameter, and are turned from cast iron or brass. Such wheels can be +purchased ready made, or it may be possible to obtain from some broken +toy a set which will prove suitable. + +[Illustration: Fig. 265.—Details of the Bearing which supports the Wheel +and Axle.] + +Each shaft is composed of two pieces of "Bessemer" rod held together by +a short piece of fiber rod having a hole in each end into which one end +of each piece of iron rod is driven. The wheels fit tightly on the other +end of each of these pieces. They should be spaced so as to run on rails +two inches apart. + +[Illustration: Fig. 266.—The Wheels and Axle.] + +The purpose of the fiber rod is to insulate the halves of the axle from +each other. The electric current which operates the car is carried by +the two rails which form the track, and if the axles were made in one +piece or the halves joined together so as to form an electrical +connection, the battery furnishing the current would be short-circuited, +because the current would pass along the two rails and across the axles +instead of through the motor. + +One pair of wheels are fitted with a grooved pulley one inch in +diameter. + +It is hardly necessary to say that the wheels and axles should be +perfectly aligned, and should run true. + +[Illustration: Fig. 267.—The Motor.] + +The motor used to drive the car will prove more satisfactory if +purchased ready made. A self-starting three-pole motor similar to that +shown in Figure 267 will serve very nicely. The wooden base should be +removed and the motor screwed down firmly to the floor of the car as in +Figure 268. + +One terminal of the motor is connected to one of the bearings, and the +other terminal to the other bearing. + +The motor is belted to a countershaft so that it will have sufficient +power to move the car. It cannot be directly connected or belted to the +axle, because the speed of a small motor is so high that it has +comparatively little turning power or _torque_. The speed must be +reduced and the torque increased before it will drive the car. + +The countershaft consists of two grooved pulleys mounted upon an axle +running in two bearings mounted upon the floor of the car. The bearings +are made from a strip of heavy sheet-brass, bent at right angles and +fastened to the car floor with small screws. The large pulley, _A_, is +one inch and one half in diameter and the small pulley, _B_, is +five-sixteenths of an inch in diameter. The countershaft is mounted in +such a position that a belt may be run from the small pulley, _B_, to +the pulley mounted on the axle of one pair of wheels. A belt is also run +from the small pulley on the motor to the large pulley, _A_, on the +countershaft. The pulleys must all be carefully lined up so that the +belts will run in their grooves without danger of slipping out. + +[Illustration: Fig. 268.—The Complete Truck of the Car without the +Body.] + +The shield on the platform at each end of the car is made of sheet-iron +or tin. Two small projections on the bottom are bent over at right +angles and used to secure the shields in position by driving a small +tack through them into the floor of the car. + +The steps on either side of each platform are also made by bending +strips of sheet-iron or tin and fastening them to the car with small +nails or tacks. + +The coupler consists of a strip of tin having a small hook soldered to +the end so that a trail car may be attached if desirable. + +[Illustration: Fig. 269.—Pattern for the Sides and Ends of the Car.] + +The car is now ready for testing, and when held in the hand so that the +wheels are free to run, two cells of dry battery should be found all +that is necessary to drive them at a fair rate of speed. The two wires +leading from the battery should be connected to the bearings, one wire +leading to each bearing. It will require more than two cells, however, +to drive the wheels properly when the car is on the track, All moving +parts should run freely and smoothly. The car may be used just as it is, +but if fitted with a body and a top it will present a much more +realistic appearance. + +The sides and ends of the car body are made of sheet-iron or tin. Figure +269 shows the pattern and dimensions for these parts. They may be made +from one piece of metal eighteen and one-half inches long and three and +three-quarters inches wide. The doors and windows are cut out with a +pair of tin-snips. The small projections along the top are bent down at +right angles and the roof is fastened to them. The dotted lines indicate +the places for bending these projections and also the sides and ends of +the car. + +[Illustration: Fig. 270.—The Roof of the Car.] + +The roof is made in two pieces. It also is sheet-iron or tin. The roof +proper is eight inches long and four inches wide. It has a hole five and +one-half inches long and one and three-quarters inches wide cut in the +center. A number of small projections are left and bent upward to +support the deck and to form imitation ventilators. The deck is six +inches long and two and one-quarter inches in width. It is placed in +position on the roof and fastened by soldering. The roof is fastened to +the sides and ends of the car by soldering. It must be bent slightly to +conform with the curve at the top of the front and the rear of the car. + +[Illustration: Fig. 271.—The Completed Car.] + +The car when completed will appear as in Figure 271. + +The track is made of smooth spring steel, one-half inch wide and either +No. 20 or No. 22 gauge in thickness. + +[Illustration: Fig. 272.–Details of a Wooden Tie.] + +The wooden ties are three and one-half inches long, three-quarters of an +inch wide and three-eighths of an inch thick. Each tie has two saw-cuts, +exactly two inches apart across the top face. This part of the work is +best performed in a miter-box so that the cuts will be perfectly square +across the ties. A saw should be used which will make a cut of such a +size that the steel track will fit tightly into it. + +The distance between the two rails of the track, or the "gauge," as it +is called, is two inches. + +[Illustration: Fig. 273.–Arrangement of Track.] + +The track is assembled as in Figure 273. The spring steel is forced into +the saw-cuts in the ties by tapping with a light wooden mallet. The ties +should be spaced along the track about three inches apart. The work of +laying the track must be very carefully done so that the car wheels will +not bind at any spot. Curves should not be too sharp, or the car will +not pass around. + +The track may be laid out in a number of different shapes, some of which +are shown in Figure 274. + +[Illustration: Fig. 274.—Three Different Patterns for laying out the +Track.] + +A circle is the easiest form of track to make. In laying out a circle or +any sort of curved track, the outside rail must necessarily be made +longer than the inside one. + +The oval shape is a very good form to give the track in a great many +cases, especially where it is desirable for the car to have a longer +path than that afforded by a circle. + +[Illustration: Fig. 275.—Details of the Base of the Cross-over.] + +In order to make a figure-eight out of the track, a crossing, or +"cross-over," as it is sometimes called, will be required. This is shown +in Figure 275. A cross-over permits two tracks to cross each other +without interference. It consists of a wooden base, eight inches square +and three-eighths of an inch thick. Four saw-cuts, each pair exactly +parallel, and two inches apart, are made at right angles to each other +across the top surface of the base, as shown in the illustration. + +The track used on the cross-over is semi-hard hoop-brass, one-half of an +inch wide and of the same gauge as the steel track. The brass is more +easily bent than the steel and is used for that reason, it being +practically impossible to bend the steel track at right angles without +snapping it. + +Four pieces of the brass, each five inches long, are bent at right +angles exactly in the center. Four short pieces, each one and one-half +inches long, will also be required. + +[Illustration: Fig. 276.—The Completed Cross-over.] + +The cross-over is assembled as shown in Figure 276. The strips marked +_D_ are strips of very thin sheet-brass or copper. The purpose of these +strips is to connect the ends of the track on the cross-over to the ends +of the track forming the figure-eight so that the cross-over will not be +a "dead" section, that is, a section of track where the car cannot get +any current. + +The long strips, bent at right angles to each other and marked _A_, _A_, +_B_, _B_, in the illustration, are forced into the saw-cuts in the base +over the strips marked _D_. + +The small pieces, _C_, _C_, _C_, _C_, are placed in between the long +strips, leaving a space between so that the flanges of the car wheels +can pass. The pieces, _C_, _C_, _C_, _C_, should form a square open at +the corners. The two long strips, _A_, _A_, should be at opposite +corners diagonally across the square. _B_ and _B_ should occupy the same +relative position at the other corners. _A_ and _A_ are connected +together and _B_ and _B_ are connected together by wires passing on the +under side of the base. + +The ends of the track forming the figure-eight are forced into the +saw-cuts at the edges of the base so that they form a good electrical +connection with the small strips marked _D_. + +It is quite necessary to use care in arranging a figure-eight track, or +there will be danger of short-circuiting the batteries. The outside +rails of the figure-eight, distinguished by the letter _B_ in the +illustration, should be connected together by the cross-over. The inside +rails, marked _A_, should also be connected together by the cross-over. + +In order to make a good mechanical and electrical connection between the +ends of the rails when two or more sections of track are used in laying +out the system, it is necessary to either solder the rails together or +else use a connector such as that shown in Figure 277. + +This consists of a small block of wood having a saw-cut across its upper +face and a piece of thin sheet-brass set into the cut. The two rails are +placed with their ends abutting and one of these connectors slipped up +from beneath and forced on the rails. The piece of thin brass set into +the wooden block serves to make an electrical connection between the two +rails and also to hold them firmly in position. A small screw and a +washer placed outside the track and passing through the brass strip will +allow a battery wire to be conveniently attached. + +[Illustration: Fig. 277.—A Connector for joining the Ends of the Rails.] + +The steel rails should be occasionally wiped with machine oil or +vaseline to prevent rusting, and also to allow the car to run more +freely wherever the flanges of the wheels rub against the rails in +passing around a curve. + +Four dry cells or three cells of storage battery should be sufficient to +operate the car properly. If it is desirable, a small rheostat may be +included in the battery circuit, so that the speed of the car can be +varied at will. The motor and the wheels should be carefully oiled so +that they will run without friction. The belts should not be so tight +that they cause friction or so loose that they allow the motor to slip, +but should be so adjusted that the motor runs freely and transmits its +power to the wheels. + +The car may be made reversible by fitting with a small current reverser, +but unless the reverser is carefully made the danger of loss of power +through poor contacts is quite considerable. If the car is fitted with a +reverser the handle should be arranged to project from the car in a +convenient place where it can be easily reached by the fingers and the +car sent back or forth at will. + +A railway system such as this can be elaborated and extended by adding +more than one car to the line or such features as bridges and stations. + +[Illustration: Fig. 278.—A Bumper for preventing the Car from leaving +the Rails.] + +The ends of a blind section of track, that is, a straight piece of track +not part of a circle or curve so that the car can return, should be +fitted with a track bumper, to prevent the car leaving the rails. + +[Illustration: Fig. 279.—A Design for a Railway Bridge.] + +No dimensions are given in Figures 279 and 280, showing designs for a +bridge and a station, because they are best left to be determined by the +scale upon which the railway system is to be extended. + +[Illustration: Fig. 280.—A Design for a Railway Station.] + +Both the bridge and the station are very simple. The bridge is built +entirely of wood, with the exception of the steel rails. + +The station may be made out of thin wood, such as cigar-box wood. The +doors, windows, etc., may be painted on the walls. If this is carefully +done, it will give a very realistic appearance to your station. + + + +CHAPTER XIX MINIATURE LIGHTING + + +Miniature lighting is a field of many interesting possibilities for the +young experimenter. Any labor expended along this line will result in +something far more useful from a practical standpoint than almost any of +the other things described in this book. + +Miniature lights, operated from batteries, may be used in various ways; +to light dark corners, hallways, or other places where a light is often +temporarily wanted without the accompanying danger and nuisance of +matches or kerosene lamps. + +Miniature lighting has only been made practical by the tungsten filament +lamp. The filament, or wire inside the globe, which becomes hot and +emits the light when the current is turned on, is made of _tungsten_ in +a tungsten lamp. In the earlier lamps, it was made of carbon. The carbon +lamp is now seldom used and is highly inefficient when compared to the +tungsten. + +*A Carbon Lamp* consumes about three and one-half watts of current for +each candle-power of light, whereas a small tungsten lamp uses only +about one watt per candle-power small tungsten lamp uses only about one +watt per candle-power. The tungsten lamp is therefore three times as +efficient as a carbon lamp, and when used on a battery of equal voltage +it is possible to obtain the same amount of light with one-third of the +current that would be required by a carbon lamp. + +[Illustration: Fig. 281.—Miniature Carbon Battery Lamp.] + +Carbon lamps similar to that shown in Figure 281 are made in a number of +different voltages. The lowest voltage that it is practically possible +to make a carbon lamp for is three and one-half. A three-and-one-half +volt carbon lamp is designed to be operated on small dry cells such as +flashlight batteries. The E. M. F. of a dry cell is about one and +one-half volts, but when three small dry cells of the flashlight type +are connected in series and used to operate a lamp, their voltage +"drops," and the available E. M. F. is only about three and one-half +volts. + +Four-volt carbon lamps are intended to be operated on large dry +batteries or wet cells because they do not lose their voltage as quickly +as small dry cells. The table below gives the voltage and candle-power +of the various small carbon lamps which are carried in stock by most +electrical dealers or supply houses: + +*MINIATURE CARBON BATTERY LAMPS* + +3.5 volts for flashlight batteries + +4 volts. 2 candle-power + +5.5 volts for flashlight batteries + +6 volts. 2 candle-power + +6 volts. 4 candle-power + +8 volts. 4 candle-power + +10 volts. 6 candle-power + +*Tungsten Lamps* are made for voltages as low as one and one-half, and +will light on one cell of dry battery. The range of voltages is quite +wide and varied. A few of the most common sizes are given below: + +*MINIATURE TUNGSTEN BATTERY LAMPS* + +1.5 volts. for one dry cell + +2.5 volts. for two-cell flashlight battery + +2.8 volts. for two-cell flashlight battery + +3.5 volts. for three-cell flashlight battery + +3.8 volts. for three-cell flashlight battery + +4 volts. 4 candle-power + +6 volts. 2 candle-power + +6 volts. 4 candle-power + +6 volts. 6 candle-power + +6 volts. 8-10-12-16-20-24 candle-power + +[Illustration: Fig. 282.—Miniature Tungsten Battery Lamp.] + +To find the approximate amount of current drawn from a battery by a +tungsten lamp, divide the candle-power by the voltage and the result +will be the current in amperes. For example, a 6 v. 2 c. p. lamp will +require, 2 divided by 6, or one-third of an ampere. + +Six-volt tungsten lamp giving a light greater than six candle-power are +only used on storage batteries and are employed principally for +automobile lighting. + +The filament of a tungsten lamp is much longer than that of a carbon +lamp and is usually in the form of a spiral or helix, as shown in Figure +282. + +The bases of battery lamps, the base being the lower portion of the +lamp, which is made of brass and fits into a socket or receptacle, are +made in three different styles: _miniature_, _candelabra_, and +_Ediswan_. + +[Illustration: Fig. 283.—Lamps fitted respectively with Miniature, +Candelabra, and Ediswan Bases.] + +The miniature and candelabra bases have a threaded brass shell on the +outside and a small brass contact-button on the bottom. They are similar +except in respect to size. The miniature base is smaller than the +candelabra. The Ediswan base is a plain brass shell having two pins on +the side and two contacts on the bottom. This type of base is only used +in this country on automobiles. The miniature and the candelabra bases +are standard for battery lighting. The miniature base has many +advantages over the candelabra for the young experimenter, and should be +adopted in making any of the apparatus described in this chapter. These +three bases are shown in Figure 283. + +[Illustration: Fig. 284.—Miniature Flat-Base Porcelain Receptacle.] + +In order to form a good electrical connection between the lamp and the +power wires some sort of a receptacle or socket is necessary. The most +common arrangement for this purpose is the miniature flat-base porcelain +receptacle shown in Figure 284. This type of receptacle is used in +places where it can be permanently fastened in position with two small +screws. + +[Illustration: Fig. 285.—Weather-proof and Pin-Sockets.] + +The devices shown in Figure 285 are known respectively as a porcelain +weather-proof socket and a pin-socket. Sockets similar to the +weather-proof socket are also made of wood. The weather-proof sockets +are used in places where the light is to be exposed out-of-doors, as for +instance on a porch. The small metal parts are sealed in the porcelain +and entirely protected. + +The pin-sockets and the wooden sockets are used principally on Christmas +trees or in decorative outfits where lamps are hung in festoons. The +flat-base receptacle, the pin-socket, and also the wooden socket will be +found very useful in making the apparatus described farther on in this +chapter. + +*The Wires* used to carry the current in a miniature lighting system may +be of the sort known as _annunciator_ or _office_ wire if the wires are +to be run entirely indoors. The wire should not be smaller than No. 16 +B. & S. gauge. When the wires are run outdoors, on a porch, or in some +other place exposed to the weather, the wire used should be +rubber-covered. Hanging lights or lights intended to be adjustable +should be connected with "flexible conductor." This is made of a number +of very fine wires braided together and insulated with silk. The wires +used in a lighting system should not in any case be longer than it is +necessary to have them. When a battery is connected to a system of wires +it is found that the voltage at the end of the wires is much lower than +at a point near the battery. This is called voltage "drop," and is much +greater as the wires grow longer. A light placed at the end of two very +long wires will not burn as brightly as it would if connected to the +same battery by means of short wires. + +*Switches* can be made by following the suggestions given in Chapter +VII. Suitable switches can be purchased for a few cents at a most any +electrical house and will prove very much neater and efficient. They +should preferably be of any of the types shown in Figure 286. + +*The Batteries* used for miniature lighting may be made up of storage +cells, dry cells or carbon cylinder cells. Storage cells will prove the +most satisfactory, provided that the experimenter has some convenient +means of recharging them or of having them recharged. Storage cells will +be found of especial value wherever it is desirable to operate several +lights from one battery. + +Carbon cylinder cells are only suitable where one cell is to be operated +at a time. If more than one is used, the battery is liable to become +polarized and the lamps will not burn brightly. Carbon cylinder +batteries are very inexpensive to renew, and will be found the cheapest +method of lighting a small tungsten lamp. + +[Illustration: Fig. 286.—Types of Battery Switches suitable for +Miniature Lighting.] + +If lamps requiring more than two amperes are to be operated on dry +cells, the latter should be connected in series-multiple, as shown in +Figure 69. Two sets of dry cells connected in series-multiple will give +more than twice the service of a single set. + +Lamps may be connected either in multiple or in series, provided that +the proper voltages of both battery and lamps are used. + +When they are to be connected in multiple, the voltage of the lamps +should be the same as that of the battery. When they are to be used in +series, the voltage of the lamps multiplied by the number used should +equal the voltage of the battery. For example, suppose that you wish to +use a number of six-volt lamps on a six-volt storage battery. In that +case they must be connected in multiple. But if it should be that the +lamps are only two-volt lamps and you wish to operate three of them on a +six-volt battery you will have to place them in series. + +[Illustration: Fig. 287.—How Lamps are Connected in Multiple.] + +[Illustration: Fig. 288.—How Lamps are Connected in Series.] + +It is sometimes desirable to arrange a lamp and two switches so that it +can be turned off or on from either switch independently of the other. +This is called "three-way wiring," and is a very convenient method of +arranging a light in a hallway. If one switch is placed at the top of a +stairway and the other switch at the bottom, a person can pass upstairs +or downstairs, light the lamp ahead, and turn it out as he passes the +last switch, no matter in which direction the previous user of the light +may have gone. + +The switches are two-point switches, and the circuit should be arranged +as in Figure 289. + +The switch-levers should always rest on one of the contacts and never be +left between, as shown in the drawing. + +[Illustration: Fig. 289.—Three-way Wiring Diagram. The Light may be +turned off or on from either Switch.] + +They are represented that way in the illustration in order not to +conceal the contacts. + +Small brackets made of brass and similar to that shown in Figure 290 are +for sale at many electrical supply houses, and will add a very realistic +appearance to a miniature lighting plant. + +[Illustration: Fig. 290.—A Lamp Bracket for Miniature Lighting.] + +Brackets may be constructed after the plan shown in Figure 291. A wooden +socket or a pin-socket is mounted on the end of a small piece of brass +tubing which has been bent into the shape shown in the illustration. The +other end of the tube is set into a wooden block so that the bracket may +be mounted on the wall. The wires from the socket lead through the brass +tube and through the back or top of the block. + +[Illustration: Fig. 291.—A Home-made Bracket.] + +Hanging lights may be arranged by fitting a wooden socket and a lamp +with a reflector as shown in Figure 296. The reflector consists of a +circular piece of tin or sheet-aluminum having a hole in the center +large enough to pass the base of a miniature lamp. The circle is then +cut along a straight line from the circumference to the center. If the +edges are pulled together and lapped the circular sheet of metal will +take on a concave shape and form a shade or reflector which will throw +the light downwards. The overlapping edges of the reflector should be +soldered or riveted together. The reflector is slipped over the base of +the lamp, a small rubber or felt washer having been placed over the base +next to the glass bulb so that the reflector will not break the lamp. +The lamp is then screwed into a socket and allowed to hang downwards +from a flexible conductor. + +[Illustration: Fig. 292.—A Hanging Lamp.] + +A very pretty effect can be secured by drilling the edges of a reflector +full of small holes about three-sixteenths of an inch apart and then +hanging short strings of beads from the holes. The beads should form a +hanging fringe around the edge of the reflector, and if they are of +glass, a pleasing brilliancy is produced. Figure 293 shows how to make +the reflector. + +[Illustration: Fig. 293.—How the Reflector is made.] + +The batteries for a miniature lighting plant may be located in a closet, +under a stairway, or in some other out-of-the-way place. Wires from +there may be extended to various parts of the house, such as hallways, +closets, the cellar stairs, over a shaving-mirror in the bath-room or in +any dark corner where a light is often temporarily needed. The wires can +be run behind picture-mouldings or along the surbase and be almost +entirely concealed. + +[Illustration: Fig. 294.—A Three-Cell Dry Battery for use in +Hand-Lanterns, etc.] + +*Small Batteries* consisting of three small dry cells enclosed in +cardboard box, as shown in Figure 294, are on the market, and may be +bought at prices ranging from thirty to forty cents, depending upon the +size and the maker. One of the most convenient and practical sizes of +this type of battery has the dimensions shown in the illustration, and +with its aid it is possible to construct a number of very useful +electrical novelties and household articles in the shape of portable +electric lamps, etc. These batteries are quite small and are only +intended to operate very small lamps. Only one lamp should be used on +each battery at a time, and it should not be allowed to burn long. Some +of these batteries will give ten to fourteen hours of intermittent +service but if allowed to burn continuously would only light the lamp +for about five hours at the most. It is much the better plan to use them +only for a few minutes at a time, and then turn the light off and allow +the battery to recuperate. + +*An Electric Hand-Lantern* is a very convenient device which is quite +simple to make. It consists of a wooden box large enough to receive a +three-cell battery, such as that shown in Figure 295. The back of the +box should open and close on hinges and be fastened with a hook so that +the battery may be easily removed for renewal. + +[Illustration: Fig. 295.—An Electric Hand-Lantern.] + +A three-and-one-half-volt tungsten lamp is mounted on the front of the +lantern and connected with the battery and a switch so that the light +can be turned on and off at will. The switch may be placed at the top of +the box so that the fingers of the same hand used to carry the lantern +may be used to turn the light on and off. The lantern is fitted with a +leather strap at the top, to be convenient for carrying. + +*The Ruby Lantern* shown in Figure 296 is somewhat similar in +arrangement to the lantern just described, which may be used both as a +hand-lantern and a ruby light for developing photographs. + +[Illustration: Fig. 296.—An Electric Ruby Lantern.] + +It consists of a wooden box to hold a three-cell dry battery, and is +provided with a handle so that it may be easily carried. A switch by +which to turn the lamp on and off is mounted on the side of the box. + +The light is furnished by a three-and-one-half-volt tungsten lamp +mounted on the front of an inclined wooden board arranged as shown in +the illustration so as to throw the light downward. The sides and bottom +of the box are grooved near the front edges so that a piece of ruby +glass may be inserted. Ruby glass for this purpose may be purchased at +almost any store dealing in photographers’ supplies. + +The top is provided with a shield which is fastened in position by means +of four small hooks after the glass is in place. The shield is used in +order to prevent any white light from escaping through the crack between +the glass and the top of the box. A ruby lamp of this sort must be made +absolutely "light-tight" so that the only light emitted is that which +passes through the ruby glass. If any white light escapes it is liable +to fog and spoil any pictures in process of development. + +[Illustration: Fig. 297.—The Electric Ruby Lamp with Glass and Shield +Removed.] + +By removing the ruby glass and the shield, as shown in Figure 297, the +light is changed into a hand-lantern. The back of the box should be made +removable so that the battery can be replaced when worn out. + +*A Night-Light* arranged to shine on the face of the clock so that the +time may be easily told during the night without inconvenience is shown +in Figure 298. + +[Illustration: Fig. 298.—An Electric Night-Light for telling the Time +during the Night.] + +It consists of a flat wooden box containing a three-cell dry battery and +having a small three-and-one-half-volt tungsten lamp mounted on the top +in the front with room for a clock to stand behind. The battery and the +lamp are connected to a switch so that the light may be turned on and +off. By attaching a long flexible wire and a push-button of the +"pear-push" type it is possible to place the light on a table and run +the wire with the push-button attached over to the bed so that one may +see the time during the night without getting up. The bottom of the box +should be made removable so that a new battery may be inserted when the +old one is worn out. + +*The Watch-Light* is in many ways similar to the clock light just +described—but is smaller. It consists of a box just large enough to +receive a three-cell flashlight battery. A piece of brass rod is bent +into the form of a hook or crane from which to suspend the watch. + +[Illustration: Fig. 299.—A Watch-Light.] + +The light is supplied by a three-and-one-half-volt tungsten flashlight +bulb mounted on the top of the box in front of the watch. If desirable, +the light may be fitted with a small shade or reflector so that it +shines only on the dial and not in the eyes. The figures on the face of +the timepiece can then be seen much more plainly. + +The lamp is mounted in a small wooden socket or a pin-socket passing +through a hole in the top of the box, so that the wires are concealed. A +small push-button is located in one of the forward corners of the box, +so that when it is pressed the lamp will light. Two small binding-posts +mounted at the lower right-hand corner of the box are connected directly +across the terminals of the switch, so that a flexible wire and a +push-button can be connected, and the light operated from a distance. + +*An Electric Scarf-Pin* can be made by almost any boy who is skillful +with a pocket-knife. The material from which the pin is made may be a +piece of bone, ivory, or meerschaum. It is carved into shape with the +sharp point of a penknife and may be made to represent a skull, dog’s +head, an owl, or some other simple figure. The inside is hollowed out to +receive a "pea" lamp. Pea lamps with a cord and a plug attached as shown +in Figure 300 may be purchased from almost any electrical supply house. +The lamp is a miniature carbon bulb about one-eighth of an inch in +diameter. The eyes, nose, and mouth of the figure are pierced with small +holes, so that when the lamp is lighted the light will show through the +holes. The figure should be carved down thin enough to be translucent +and light up nicely. + +[Illustration: Fig. 300.—A "Pea" Lamp attached to a Flexible Wire and a +Plug.] + +A large pin is cemented or otherwise fastened to the back of the figure +so that it can be placed on the necktie or the lapel of the coat. The +lamp is removed from the socket of an electric flashlight and the plug +attached to the pea lamp screwed into its place. The pea lamp is +inserted inside the figure and bound in place with some silk thread. +Then when the button is pressed on the flashlight case, the pin will +light up and tiny beams of light will shoot out from the eyes, nose, and +mouth of the figure. + +[Illustration: Fig. 301.—Four Steps in Carving a Skull Scarf-Pin. 1. The +Bone. 2. Hole drilled in Base. 3. Roughed out. 4. Finished.] + +The drawings in Figure 301 show how to carve a skull scarf-pin. It is +made from a cylindrical piece of bone about five-eighths of an inch long +and three-eighths of an inch in diameter. The first operation is to +drill a hole three-eighths of an inch deep into the bottom. The hole +should be large enough in diameter to pass the pea lamp. + +[Illustration: Fig. 302.—The Completed Pin ready to be connected to a +Battery by removing the Lamp from a Flashlight and screwing the Plug +into its Place.] + +Then carve the eyes and nose and teeth. The drawings will give a good +idea of the steps in this part of the work. Next round off the top of +the skull. Bore a small hole in the back to receive the pin. Put the +light inside of the skull, and after it is bound in position the +scarf-pin is finished. + + + +CHAPTER XX MISCELLANEOUS ELECTRICAL APPARATUS + + +HOW ELECTRICITY MAY BE GENERATED FROM HEAT + + +For the past century there has been on the part of many scientists and +inventors a constant endeavor to "harness the sunlight." The power which +streams down every day to our planet is incalculable. The energy +consumed in the sun and thrown off in the form of heat is so great that +it makes any earthly thing seem infinitesimal. We can only feel the heat +from a large fire a few feet away, yet the scorching summer heat travels +90,000,000 miles before it reaches us, and even then our planet is +receiving only the smallest fractional part of the total amount +radiated. + +Dr. Langley of the Smithsonian Institute estimated that all the coal in +the State of Pennsylvania would be used by the sun in a fraction of a +second if it were sent up there to supply energy. + +Perhaps, some day in the future, electric locomotives will haul their +steel cars swiftly from city to city by means of electricity, generated +with "sun power." Perhaps energy from the same source will heat our +dwellings and furnish us light and power. + +This is not an idle dream, but may some day be an actuality. It has +already been carried out to some extent. A Massachusetts inventor has +succeeded in making a device for generating electricity from sun energy. + +The apparatus consists of a large frame, in appearance very much like a +window. The glass panes are made of violet glass, behind which are many +hundred little metallic plugs. The sun’s heat, imprisoned by the violet +glass, acts on the plugs to produce electricity. One of these generators +exposed to the sun for ten hours will charge a storage battery and +produce enough current to run 30 large tungsten lamps for three days. + +[Illustration: Fig. 303.—How the Copper Wires (_C_) and the Silver Wires +(_I_) are twisted together in Pairs.] + +The principle upon which the apparatus works was discovered by a +scientist named Seebeck, in 1822. He succeeded in producing a current of +electricity by heating the points of contact between two dissimilar +metals. + +Any boy can make a similar apparatus, which, while not giving enough +current for any practical purpose, will serve as an exceedingly +interesting and instructive experiment. + +Cut forty or fifty pieces of No. 16 B. & S. gauge German silver wire +into five-inch pieces. Cut an equal number of similar pieces of copper +wire, and twist each German silver wire firmly together with one of +copper so as to form a zig-zag arrangement as in Figure 303. + +[Illustration: Fig. 304.—Wooden Ring.] + +Next make two wooden rings about four inches in diameter by cutting them +out of a pine board. Place the wires on one of the rings in the manner +shown in Figure 305. Place the second ring on top and clamp it down by +means of two or three screws. + +[Illustration: Fig. 305.—Complete Thermopile. An Alcohol Lamp should be +lighted and placed so that the Flame heats the Inside Ends of the Wires +in the Center of the Wooden Ring.] + +The inner junctures of the wires must not touch each other. The outer +ends should be bent out straight and be spaced equidistantly. The ring +should be supported by three iron rods or legs. The two terminals of the +thermopile as the instrument is called, should be connected to +binding-posts. + +Place a small alcohol lamp or Bunsen burner in the center, so that the +flame will play on the inner junctures of the wires. A thermopile of the +size and type just described will deliver a considerable amount of +electrical energy when the inside terminals are good and hot and the +outside terminals fairly good. + +The current may be very easily detected by connecting the terminals to a +telephone receiver or galvanometer. By making several thermopiles and +connecting them in parallel, sufficient current can be obtained to light +a small lamp. + + +HOW TO MAKE A REFLECTOSCOPE + + +A reflectoscope is a very simple form of a "magic lantern" with which it +is possible to show pictures from post-cards, photographs, etc. The +ordinary magic lantern requires a transparent lantern slide, but the +reflectoscope will make pictures from almost anything. The picture +post-cards or the photographs that you have collected during your +vacation may be thrown on a screen and magnified to three or four feet +in diameter. Illustrations clipped from a magazine or newspaper or an +original sketch or painting will likewise show just as well. Everything +is projected in its actual colors. If you put your watch in the back of +the lantern, with the wheels and works exposed, it will show all the +metallic colors and the parts in motion. + +[Illustration: Fig. 306.—A Reflectoscope.] + +The reflectoscope, shown in Figure 306, consists of a rectangular box +nine inches long, six inches wide, and six inches high outside. It may +be built of sheet-iron or tin, but is most easily made from wood. Boards +three-eighths of an inch thick are heavy enough. The methods of making +an ordinary box are too simple to need description. The box or case in +this instance, however, must be carefully made and be "light-tight," +that is, as explained before, it must not contain any cracks or small +holes which will allow light to escape if a lamp is placed inside. + +A round hole from two and one-half to three inches in diameter is cut in +the center of one of the faces of the box. + +The exact diameter cannot be given here because it will be determined by +the lens which the experimenter is able to secure for his reflectoscope. +Only one lens is required. It must be of the "double-convex" variety, +and be from two and one-half to three inches in diameter. A lens is very +easily secured from an old bicycle lantern. It should be of clear glass. + +[Illustration: Fig. 307.—How the Lens is Arranged and Mounted.] + +A tube, six inches long and of the proper diameter to fit tightly around +the lens, must be made by rolling up a piece of sheet-tin and soldering +the edges together. This tube is the one labeled "movable tube" in the +illustrations. A second tube, three inches long and of the proper +diameter to just slip over the first tube, must also be made. A flat +ring cut from stiff sheet-brass is soldered around the outside of this +second tube, so that it may be fastened to the front of the case by +three or four small screws in the manner shown. The hole in the front of +the box should be only large enough to receive the tube. + +The lens is held in position near one end of the movable tube by two +strong wire rings. These rings should be made of wire that is heavy and +rather springy, so that they will tend to open against the sides of the +tube. It is a good plan to solder one of them in position, so that it +cannot move, and then put in the lens. After the lens is in position, +the second ring should be put in and pushed down against the lens. Do +not attempt to put the lens in, however, until you are sure that the +metal has cooled again after soldering, or it will be liable to crack. + +[Illustration: Fig. 308.—A View of the Reflectoscope from the Rear, +showing the Door, etc.] + +The back of the box contains a small hinged door about four inches high +and five and one-half inches long. The pictures that it is desired to +project on the screen are held against this door by two small brass +clips, as shown in Figure 308. + +[Illustration: Fig. 309.—A View of the Reflectoscope with the Cover +removed, showing the Arrangement of the Lamps, etc.] + +The light for the reflectoscope is most conveniently made by two +16-candle-power electric incandescent lamps. Figure 309 shows a view of +the inside of the box with the cover removed, looking directly down. The +lamps fit into ordinary flat-base porcelain receptacles, such as that +shown in Figure 310. Two of these receptacles are required, one for each +lamp. They cost about ten cents each. + +[Illustration: Fig. 310.—A Socket for holding the Lamp.] + +The reflectors are made of tin, bent as shown in Figure 311. They are +fastened in position behind the lamps by four small tabs. + +It is possible to fit a reflectoscope with gas or oil lamp to supply the +light, but in that case the box will have to be made much larger, and +provided with chimneys to carry off the hot air. + +The interior of the reflectoscope must be painted a dead black by using +a paint made by mixing lampblack and turpentine. The interior also +includes the inside of the tin tubes. + +The electric current is led into the lamps with a piece of flexible +lamp-cord passing through a small hole in the case. An attachment-plug +is fitted to the other end of the cord, so that it may be screwed into +any convenient lamp-socket. + +[Illustration: Fig. 311.—The Tin Reflector.] + +The pictures should be shown in a dark room and projected on a smooth +white sheet. They are placed under the spring clips on the little door +and the door closed. The movable tube is then slid back and forth until +the picture on the screen becomes clear and distinct. + +The lantern may be improved considerably by using tungsten lamps of 22 +c. p. each in place of ordinary c. p. carbon filament lamps. + +If four small feet, one at each corner, are attached to the bottom of +the case, its appearance will be much improved. + +Very large pictures will tend to appear a little blurred at the corners. +This is due to the lens and cannot be easily remedied. + + +HOW TO REDUCE THE 110-v. CURRENT SO THAT IT MAY BE USED FOR +EXPERIMENTING + + +Oftentimes it is desirable to operate small electrical devices from the +110-v. lighting or power circuits. Alternating current can be reduced to +the proper voltage by means of a small step-down transformer, such as +that described in Chapter XIII. Direct current may be reduced by means +of a resistance. The most suitable form of resistance for the young +experimenter to use is a "lamp bank." + +A lamp bank consists of a number of lamps connected in parallel, and +arranged so that any device may be connected in series with it. + +The lamps are set in sockets of the type known as "flat-base porcelain +receptacles," such as that shown in Figure 310, mounted in a row upon a +board and connected as shown in Fig. 312. + +The current from the power line enters through a switch and a fuse and +then passes through the lamps before it reaches the device it is desired +to operate. The switch is for the purpose of shutting the current on and +off, while the fuse will "blow" in case too much current flows in the +circuit. + +The amount of current that passes through the circuit may be accurately +controlled by the size and number of lamps used in the bank. The lamps +may be screwed in or out and the current altered by one-quarter of an +ampere at a time if desirable. + +The lamps should be of the same voltage as the line upon which they are +to be used. Each 8-candle-power, 110-v. carbon lamp used will permit +one-quarter of an ampere to pass. Each 16-candle-power, 110-v. lamp will +pass approximately one-half an ampere. A 32-candle-power lamp of the +same voltage will permit one ampere to flow in the circuit. + +[Illustration: Fig 312.—Top View of Lamp Bank, showing how the Circuit +is arranged. A and B are the Posts to which should be connected any +Device it‘s desirable to operate.] + + +AN INDUCTION MOTOR + + +*An Induction Motor* is a motor in which the currents in the armature +windings are _induced_. An induction motor runs without any brushes, and +the current from the power line is connected only to the field. The +field might be likened to the primary of a transformer. The currents in +the armature then constitute a secondary winding in which currents are +induced in the same manner as in a transformer. + +An induction motor will operate only on alternating current. + +A small motor such as that shown in Figure 267, and having a three-pole +armature, is the best type to use in making an experimental induction +motor. + +Remove the brushes from the motor and bind a piece of bare copper wire +around the commutator so that it short-circuits the segments. + +A source of alternating current should then be connected to the +terminals of the field coil. If you have a step-down transformer, use it +for this purpose, but otherwise connect it in series with a lamp bank +such as that just described. + +Place a switch in the circuit so that the current may be turned on and +off. Wind a string around the end of the armature shaft so that it may +be revolved at high speed by pulling the string in somewhat the same +manner that you would spin a top. When all is ready, give the string a +sharp pull and immediately close the switch so that the alternating +current flows into the field. + +If this is done properly, the motor will continue to run at high speed, +and furnish power if desirable. + +Most of the alternating-current motors in every-day use for furnishing +power for various purposes are induction motors. They are, however, +self-starting, and provided with a hollow armature, which contains a +centrifugal governor. When the motor is at rest or just starting, four +brushes press against the commutator and divide the armature coils into +four groups. After the motor has attained the proper speed, the governor +is thrown out by centrifugal force and pushes the brushes away from the +commutator, short-circuiting all the sections and making each coil a +complete circuit of itself. + + +ELECTRO-PLATING + + +Water containing chemicals such as sulphate of copper, sulphuric acid, +nitrate of nickel, nitrate of silver, or other metallic salts is a good +conductor of electricity. Such a liquid is known as an _electrolyte_. + +It has been explained in Chapter IV that chemical action may be used to +produce electricity and that in the case of a cell such as that invented +by Volta, the zinc electrode gradually wastes away and finally enters +into solution in the sulphuric acid. + +It is possible exactly to reverse this action and to produce what is +known as _electrolysis_. If an electrolyte in which a metal has been +"dissolved" is properly arranged so that a current of electricity may be +passed through the solution, the metal will "plate out," or appear again +upon one of the electrodes. + +Electrolysis makes possible electro-plating and thousands of other +exceedingly valuable and interesting chemical processes. + +More than one-half of all the copper produced in the world is produced +_electrolytically_. + +Practically all plating with gold, silver, copper and nickel is +accomplished with the aid of electricity. + +These operations are carried out on a very large scale in the various +factories, but it is possible to reproduce them in any boy’s workshop or +laboratory, with very simple equipment. + +The proper chemicals, a tank, and a battery are the only apparatus +required. The current must be supplied by storage cells or a bichromate +battery because the work will require five or six amperes for quite a +long period. + +A small rectangular glass jar will make a first class tank to hold the +electrolyte. + +The simplest electro-plating process, and the one that the experimenter +should start with is copper-plating. + +Fill the tank three-quarters full of pure water and then drop in some +crystals of copper-sulphate until the liquid has a deep blue color and +will dissolve no more. + +Obtain two copper rods and lay them across the tank. Cut two pieces of +sheet copper having a tongue at each of two corners so that they can be +hung in the solution, as shown in Figure 313. Hang both of the sheets +from one of the copper rods. Connect this rod to the _positive_ pole of +the battery. These sheets are known as the anodes. + +Then if a piece of carbon, or some metallic object is hung from the +other rod and connected to the _negative_ pole of the battery, the +electro-plating will commence. The apparatus should be allowed to run +for about half an hour and then the object hung from the rod connected +to the negative pole of the battery should be lifted out and examined. +It will be found thickly coated with copper. It is absolutely necessary +to have the poles of the battery connected in the manner stated, or no +deposit of copper will take place. + +Objects which are to be electro-plated must be free from all traces of +oil or grease and absolutely clean in every respect, or the plating will +not be uniform, because it will not stick to dirty spots. + +[Illustration: Fig. 313.—A Glass Jar arranged to serve as an +Electro-Plating Tank.] + +Such articles as keys, key-rings, tools, etc., can be prevented from +rusting by coating with nickel. + +Nickel-plating is very similar to copper-plating. Instead, however, of +having two copper sheets suspended from the rod connected to the +positive pole of the battery, they must be made of nickel. + +The electrolyte is composed of one part of nickel-sulphate dissolved in +twenty parts of water to which one part of sodium-bisulphate is added. + +This mixture is placed in the tank instead of the copper-sulphate. The +objects to be plated are hung from the copper rod connected to the +negative pole of the battery. + +When the nickel-plated articles are removed from the bath they will have +a dull, white color known as "white nickel." When white nickel is +polished with a cloth wheel revolving at high speed, and known as a +buffing-wheel, it will assume a high luster. + + +HOW TO MAKE A RHEOSTAT + + +It is often desirable to regulate the amount of current passing through +a small lamp, motor, or other electrical device operated by a battery. + +This is accomplished by inserting resistance into the circuit. A +rheostat is an arrangement for quickly altering the amount of resistance +at will. + +A simple rheostat is easily made by fitting a five-point switch such as +that shown in Figure 95 with several coils of German-silver resistance +wire. German silver has much more resistance than copper wire, and is +used, therefore, because less will be required, and it will occupy a +smaller space. + +A five-point switch will serve satisfactorily in making a rheostat, but +if a finer graduation of the resistance is desired it will be necessary +to use one having more points. + +Two lines of small wire nails are driven around the outside of the +points, and a German-silver wire of No. 24 B. & S. gauge wound in +zig-zag fashion around the nails from one point to the other. + +[Illustration: Fig. 314.—A Rheostat.] + +The rheostat is placed in series with any device it is desirable to +control. When the handle is on the point to the extreme left, the +rheostat offers no resistance to the current. When the lever is placed +on the second point, the current has to traverse the first section of +the German-silver wire and will be appreciably affected. Moving the +handle to the right will increase the resistance. + +If the rheostat is connected to a motor, the speed can be increased or +decreased by moving the lever back and forth. + +In the same manner, the light from a small incandescent lamp may be +dimmed or increased. + + +A CURRENT REVERSER OR POLE-CHANGING SWITCH + + +A pole-changing or current reversing switch is useful to the +experimenter. For example, if connected to a small motor, the motor can +be made to run in either direction at will. A motor with a permanent +magnet field can be reversed by merely changing the wires from the +battery so that the current flows through the circuit in the opposite +direction. If the motor is provided with a field winding, however, the +only way that it can be made to run either way is by reversing the +field. This is best accomplished with a pole-changing switch. + +Such a switch may be made by following the same general method of +construction as that outlined on pages 107 and 108, but making it +according to the design shown in Figure 315. + +Motors such as those illustrated can be made to reverse by connecting to +a pole-changing switch in the proper manner. + +The two outside points or contacts (marked _D_ and _D_) should both be +connected to one of the brushes on the motor. The middle contact, _C_, +is connected to the other brush. + +One terminal of the field is connected to the battery. The other +terminal of the field is connected to the lever, _A_. _B_ connects to +the other terminal of the battery. + +[Illustration: Fig. 315.—A Pole-Changing Switch or Current Reverser. The +Connecting Strip is pivoted so that the Handle will operate both the +Levers, A and B.] + +When the switch handle is pushed to the left, the lever _A_ should rest +on the left-hand contact, _D_. The lever _B_ should make contact with +_C_. The motor will then run in one direction. If the handle is pushed +to the right so that the levers _A_ and _B_ make contact respectively +with _C_ and _D_ (right-hand), the motor will reverse and run in the +opposite direction. + + +A COMPLETE WIRELESS RECEIVING SET + + +Many experimenters may wish to build a wireless receiving set which is +permanently connected and in which the instruments are so mounted that +they are readily portable and may be easily shifted from one place to +another without having to disturb a number of wires. + +The receiving set shown in Figure 316 is made up of some of the separate +instruments described in Chapter XIV, and illustrates the general plan +which may be followed in arranging an outfit in this manner. + +[Illustration: COMPLETE RECEIVING SET, CONSISTING OF DOUBLE SLIDER +TUNING COIL, DETECTOR AND FIXED CONDENSER.] + +[Illustration: COMPLETE RECEIVING SET, CONSISTING OF A LOOSE COUPLER IN +PLACE OF THE TUNING COIL, DETECTOR AND FIXED CONDENSER.] + +The base is of wood, and is nine inches long, seven inches wide, and +one-half of an inch thick. + +A double-slider tuning coil, similar to that shown in Figure 203, is +fastened to the back part of the base by two small wood-screws passing +upwards through the base into the tuner heads. + +[Illustration: Fig. 316. A Complete Wireless Receiving Outfit.] + +The fixed condenser is enclosed in a rectangular wooden block which is +hollowed out underneath to receive it and then screwed down to the base +in the forward right-hand corner. + +The detector is mounted in the forward left-hand part of the base, and +in the illustration is shown as being similar to that in Figure 210. Any +type of detector may, however, be substituted. + +The tuning coil may be replaced by a loose coupler if desirable, but in +that case the base will have to be made larger. + +The telephone receivers are connected to two binding-posts mounted +alongside the detector. + +The circuit shown in Figure 218 is the one which should be followed in +wiring the set. The wires which connect the various instruments should +be passed through holes and along the under side of the base so that +they are concealed. + + +HOW TO BUILD A TESLA HIGH-FREQUENCY COIL + + +A Tesla high-frequency coil or transformer opens a field of wonderful +possibilities for the amateur experimenter. Innumerable weird and +fascinating experiments can be performed with its aid. + +When a Leyden jar or a condenser discharges through a coil of wire, the +spark which can be seen does not consist simply of a single spark +passing in one direction, as it appears to the eye, but in reality is a +number of separate sparks alternately passing in opposite directions. +They move so rapidly that the eye is unable to distinguish them. The +time during which the spark appears to pass may only be a fraction of a +second, but during that short period the current may have oscillated +back and forth several thousand times. + +If the discharge from such a Leyden jar or a condenser is passed through +a coil of wire acting as a _primary_, and the primary is provided with a +_secondary_ coil containing a larger number of turns, the secondary will +produce a peculiar current known as _high-frequency_ electricity. +High-frequency currents reverse their direction of flow or _alternate_ +from one hundred thousand to one million times a second. + +[Illustration: Fig. 317.—Illustrating the Principle of the Tesla Coil. A +Leyden Jar discharges through the Primary Coil and a High-Frequency +Spark is produced at the Secondary.] + +High-frequency currents possess many curious properties. They travel +only on the surface of wires and conductors. A hollow tube is just as +good a conductor for high-frequency currents as a solid rod of the same +diameter. High-frequency currents do not produce a shock. If you hold a +piece of metal in your hand you can take the shock from a high-frequency +coil throwing a spark two or three feet long with scarcely any sensation +save that of a slight warmth. + +The Tesla coil described below is of a size best adapted for use with a +two-inch or three-inch spark coil, or a small high-potential wireless +transformer. The purpose of the spark coil or the transformer is to +charge the Leyden jars or condenser which discharge through the primary +of the Tesla coil. + +[Illustration: Fig. 318.—Details of the Wooden Rings used as the Primary +Heads.] + +If the young experimenter wishes to make a Tesla coil which will be +suited to a smaller spark coil, for instance, one capable of giving a +one-inch spark, the dimensions of the Tesla coil herein described can be +cut exactly in half. Instead of making the secondary twelve inches long +and three inches in diameter, make it six inches long and one and +one-half inches in diameter, etc. + +*The Primary* consists of eight turns of No. 10 B. & S. gauge copper +wire wound around a drum. The heads of the drum are wooden rings, seven +inches in diameter and one-half inch thick. A circular hole four and +one-half inches in diameter is cut in the center of each of the heads. + +[Illustration: Fig. 319.—Details of the Cross Bars which support the +Primary Winding.] + +The cross bars are two and one-half inches long, three-quarters of an +inch thick and one-half of an inch wide. Six cross bars are required. +They are spaced at equal distances around the rings and fastened by +means of a _brass_ screw passing through the ring. When the drum is +completed it should resemble a "squirrel cage." + +Small grooves are cut in the cross bars to accommodate the wire. The +wires should pass around the drum in the form of a spiral and be spaced +about five-sixteenths of an inch apart. + +The ends of the wire should be fastened to binding-posts mounted on the +heads. + +*The Secondary* is a single layer of No. 26 B. & S. silk- or +cotton-covered wire wound over a cardboard tube, twelve inches long and +three inches in diameter. + +The tube should be dried in an oven and then given a thick coat of +shellac, both inside and out, before it is used. This treatment will +prevent it from shrinkage and avoid the possibility of having to rewind +the tube in case the wire should become loose. + +[Illustration: Fig. 320.—The Secondary Head.] + +The secondary is fitted with two circular wooden heads just large enough +to fit tightly into the tube, having a half-inch flange, and an outside +diameter of three and seven-eighths inches. + +*The Base* of the coil is fifteen inches long and six inches wide and is +made of wood. + +The coil is assembled by placing the primary across the base and exactly +in the center. Two long wood-screws passing through the base and into +the primary heads will hold it firmly in position. + +The secondary is passed through the center of the primary and supported +in that position by two hard rubber supports, four inches high, +seven-eighths of an inch wide and one-half of an inch thick. A brass +wood-screw is passed through the top part of each of the supports into +the secondary heads so that a line drawn through the axis of the +secondary will coincide with a similar line drawn through the axis of +the primary. + +[Illustration: A COMPLETE COHERER OUTFIT AS DESCRIBED ON PAGE 274.] + +[Illustration: THE TESLA HIGH FREQUENCY COIL.] + +The supports are made of hard rubber instead of wood, because the rubber +has a greater insulating value than the wood. High-frequency currents +are very hard to insulate, and wood does not usually offer sufficient +insulation. + +A brass rod, five inches long and having a small brass ball at one end, +is mounted on the top of each of the hard-rubber supports. The ends of +the secondary winding are connected to the brass rods. + +[Illustration: Fig. 321.—End View of the Complete Tesla Coil.] + +The lower end of each of the hard-rubber supports is fastened to the +base by means of a screw passing through the base into the support. + +In order to operate the Tesla coil, the primary should be connected in +series with a condenser and a spark-gap as shown in Figure 324. The +condenser may consist of a number of Leyden jars or of several glass +plates coated with tinfoil. It is impossible to determine the number +required ahead of time, because the length of the connecting wires, the +spark-gap, etc., will have considerable influence upon the amount of +condenser required. The condenser is connected directly across the +secondary terminals of the spark coil. + +When the spark coil is connected to a battery and set into operation, a +snappy, white spark should jump across the spark-gap. + +If the hand is brought close to one of the secondary terminals of the +Tesla coil, a small reddish-purple spark will jump out to meet the +finger. + +[Illustration: Fig. 322.—The Complete Tesla Coil.] + +Adjusting the spark-gap by changing its length and also altering the +number of Leyden jars of condenser plates will probably increase the +length of the high-frequency spark. It may be possible also to lengthen +the spark by disconnecting one of the wires from the primary +binding-posts on the Tesla coil and connecting the wire directly to one +of any one of the turns forming the primary. In this way the number of +turns in the primary is changed and the circuit is _tuned_ in the same +way that wireless apparatus is tuned by changing the number of turns in +the tuning coil or helix. + +[Illustration: Fig 323.—Showing how a Glass-Plate Condenser is built up +of Alternate Sheets of Tinfoil and Glass.] + +The weird beauty of a Tesla coil is only evident when it is operated in +the dark. The two wires leading from the secondary to the brass rods and +the ball on the ends of the rods will give forth a peculiar _brush_ +discharge. + +If you take a piece of metal in your hand and hold it near one of the +secondary terminals, the brushing will increase. If you hold your hand +near enough, a spark will jump on to the metal and into your body +without your feeling the slightest sensation. + +If one of the secondary terminals of the Tesla coil is _grounded_ by +means of a wire connecting it to the primary, the brushing at the other +terminal will increase considerably. + +Make two rings out of copper wire. One of them should be six inches in +diameter and the other one four inches in diameter. Place the small ring +inside the large one and connect them to the secondary terminals. The +two circles should be arranged so as to be _concentric_, that is, so +that they have a common center. + +The space between the two coils will be filled with a pretty brush +discharge when the coil is in operation. + +[Illustration: Fig. 324.—A Diagram showing the Proper Method of +Connecting a Tesla Coil.] + +There are so many other experiments which may be performed with a Tesla +coil that it is impossible even to think of describing them here, and +the young experimenter wishing to continue the work further is advised +to go to some library and consult the works of Nikola Tesla, wherein +such experiments are fully explained. + + +CONCLUSION + + +Unless the average boy has materially changed his habits, in recent +years, it matters not what the preface of a book may contain, for it +will be unceremoniously skipped with hardly more than a passing glance. +With this in mind, the author has tried to "steal a march" on you, and +instead of writing a longer preface, and including some material which +might properly belong in that place, has added it here in the nature of +a conclusion, thinking that you would be more likely to read it last +than first. + +Some time ago, when in search for something that might be described in +this book, I thought of some old boxes into which my things had been +packed when I had dismantled my workshop before going away to college. +They had been undisturbed for a number of years and I had almost +forgotten where they had been put. At last a large box was unearthed +from amongst a lot of dusty furniture put away in the attic. I pried the +cover off and took the things out one by one and laid them on the floor. +Here were galvanometers, microphones, switches, telegraph keys, +sounders, relays, and other things too numerous to mention. They had all +been constructed so long ago that I was considerably amused and +interested in the manner in which bolts, screws, pieces of curtain rod, +sheet-iron, brass, and other things had been taken to form various parts +of the instruments. The binding-posts had almost in every case seen +service as such on dry cells before they came into my hands. The only +parts that it had been necessary to buy were a few round-headed brass +screws and the wire which formed the magnets. In several instances, the +latter were made so that they might be easily removed and mounted upon +another instrument. The magnets on the telegraph sounder could be +removed and fitted to form part of an electric engine or motor. + +One particular thing which struck me very forcibly was the lack of +finish and the crudeness which most of the instruments showed. + +Of course it was impossible to avoid the clumsy appearance which the +metal parts possessed, since they were not originally made for the part +that they were playing, but I wished that I had taken a little more care +to true up things properly or to smooth and varnish the wood, or that I +had removed the tool-marks and dents from the metal work by a little +filing. + +If I had done so, I should now be distinctly proud of my work. That is +not to say that I am in the least ashamed of it, for my old traps +certainly served their purpose well, even if they were not ornamental +and were better back in their box. Perhaps I might be excused for +failing in this part of the work through lack of proper tools, and also +because at that time there were no magazines or books published which +explained how to do such things, and when I built my first tuning coils +and detectors nothing on that subject had ever been published. I had to +work out such problems for myself, and gave more thought to the +principles upon which the instruments operated than to their actual +construction. + +The boys who read this book have the advantage of instructions showing +how to build apparatus that has actually been built and tested. You know +what size of wire to use and will not have to find it out for yourself. +For that reason you ought to be able to give more time to the +construction of such things. The purpose of this conclusion is simply a +plea for better work. The American boy is usually careless in this +regard. He often commences to build something and then, growing tired +before it is finished, lays it aside only to forget it and undertake +something else. _Finish whatever you undertake_. The principle is a good +one. Remember also that care with the little details is what insures +success in the whole. + +If in carrying out your work, you get an idea, do not hesitate to try +it. A good idea never refused to be developed. It is not necessary to +stick absolutely to the directions that I have given. They will insure +success if followed, but if you think you can make an improvement, do +so. + +Of course, such a book as this cannot, in the nature of things, be +exhaustive, nor is it desirable, in one sense, that it should be. + +I have tried to write a book which, considered as a whole, would prove +to be exhaustive only in that it treats of almost every phase of +practical electricity. + +The principle in mind has been to produce a work which would stimulate +the inventive faculties in boys, and to guide them until face to face +with those practical emergencies in which no book can be of any +assistance but which must be overcome by common sense and the exercise +of personal ingenuity. + +The book is not as free from technical terms or phrases, as it lay in my +power to make it, because certain of those terms have a value and an +every-day use which are a benefit to the young experimenter who +understands them. + +Any one subject treated in the various chapters of the "Boy Electrician" +may be developed far beyond that point to which I have taken it. The +railroad system could be fitted with electric signals, drawbridges, and +a number of other devices. + +Many new ideas suggest themselves to the ready-witted American boy. I +shall always be pleased to hear from any boy who builds any of the +apparatus I have described, and, if possible, to receive photographs of +the work. I should be glad to be of any assistance to such a lad, but +remember that some of the drawings and text in this book required many +hours even to complete a small portion, and therefore please do not +write to ask how to build other apparatus not described herein. And, as +the future years bring new inventions and discoveries, no one now knows +but that, some day, perhaps I will write another "Boy Electrician." + + +THE END. + + +*** END OF THIS PROJECT GUTENBERG EBOOK THE BOY ELECTRICIAN *** + + + + +A Word from Project Gutenberg + + +We will update this book if we find any errors. + +This book can be found under: https://www.gutenberg.org/ebooks/63207 + +Creating the works from print editions not protected by U.S. copyright +law means that no one owns a United States copyright in these works, so +the Foundation (and you!) can copy and distribute it in the United +States without permission and without paying copyright royalties. +Special rules, set forth in the General Terms of Use part of this +license, apply to copying and distributing Project Gutenberg™ electronic +works to protect the Project Gutenberg™ concept and trademark. Project +Gutenberg is a registered trademark, and may not be used if you charge +for the eBooks, unless you receive specific permission. If you do not +charge anything for copies of this eBook, complying with the rules is +very easy. You may use this eBook for nearly any purpose such as +creation of derivative works, reports, performances and research. They +may be modified and printed and given away – you may do practically +_anything_ in the United States with eBooks not protected by U.S. +copyright law. Redistribution is subject to the trademark license, +especially commercial redistribution. + + + + +The Full Project Gutenberg License + + +_Please read this before you distribute or use this work._ + +To protect the Project Gutenberg™ mission of promoting the free +distribution of electronic works, by using or distributing this work (or +any other work associated in any way with the phrase “Project +Gutenberg”), you agree to comply with all the terms of the Full Project +Gutenberg™ License available with this file or online at +https://www.gutenberg.org/license. + + + +Section 1. General Terms of Use & Redistributing Project Gutenberg™ +electronic works + + +*1.A.* By reading or using any part of this Project Gutenberg™ +electronic work, you indicate that you have read, understand, agree to +and accept all the terms of this license and intellectual property +(trademark/copyright) agreement. If you do not agree to abide by all the +terms of this agreement, you must cease using and return or destroy all +copies of Project Gutenberg™ electronic works in your possession. If you +paid a fee for obtaining a copy of or access to a Project Gutenberg™ +electronic work and you do not agree to be bound by the terms of this +agreement, you may obtain a refund from the person or entity to whom you +paid the fee as set forth in paragraph 1.E.8. + +*1.B.* “Project Gutenberg” is a registered trademark. It may only be +used on or associated in any way with an electronic work by people who +agree to be bound by the terms of this agreement. There are a few things +that you can do with most Project Gutenberg™ electronic works even +without complying with the full terms of this agreement. See paragraph +1.C below. There are a lot of things you can do with Project Gutenberg™ +electronic works if you follow the terms of this agreement and help +preserve free future access to Project Gutenberg™ electronic works. See +paragraph 1.E below. + +*1.C.* The Project Gutenberg Literary Archive Foundation (“the +Foundation” or PGLAF), owns a compilation copyright in the collection of +Project Gutenberg™ electronic works. Nearly all the individual works in +the collection are in the public domain in the United States. If an +individual work is unprotected by copyright law in the United States and +you are located in the United States, we do not claim a right to prevent +you from copying, distributing, performing, displaying or creating +derivative works based on the work as long as all references to Project +Gutenberg are removed. Of course, we hope that you will support the +Project Gutenberg™ mission of promoting free access to electronic works +by freely sharing Project Gutenberg™ works in compliance with the terms +of this agreement for keeping the Project Gutenberg™ name associated +with the work. You can easily comply with the terms of this agreement by +keeping this work in the same format with its attached full Project +Gutenberg™ License when you share it without charge with others. + + +*1.D.* The copyright laws of the place where you are located also govern +what you can do with this work. Copyright laws in most countries are in +a constant state of change. If you are outside the United States, check +the laws of your country in addition to the terms of this agreement +before downloading, copying, displaying, performing, distributing or +creating derivative works based on this work or any other Project +Gutenberg™ work. The Foundation makes no representations concerning the +copyright status of any work in any country outside the United States. + +*1.E.* Unless you have removed all references to Project Gutenberg: + +*1.E.1.* The following sentence, with active links to, or other +immediate access to, the full Project Gutenberg™ License must appear +prominently whenever any copy of a Project Gutenberg™ work (any work on +which the phrase “Project Gutenberg” appears, or with which the phrase +“Project Gutenberg” is associated) is accessed, displayed, performed, +viewed, copied or distributed: + + This eBook is for the use of anyone anywhere in the United + States and most other parts of the world at no cost and with + almost no restrictions whatsoever. You may copy it, give it away + or re-use it under the terms of the Project Gutenberg License + included with this eBook or online at https://www.gutenberg.org + . If you are not located in the United States, you’ll have to + check the laws of the country where you are located before using + this ebook. + +*1.E.2.* If an individual Project Gutenberg™ electronic work is derived +from texts not protected by U.S. copyright law (does not contain a +notice indicating that it is posted with permission of the copyright +holder), the work can be copied and distributed to anyone in the United +States without paying any fees or charges. If you are redistributing or +providing access to a work with the phrase “Project Gutenberg” +associated with or appearing on the work, you must comply either with +the requirements of paragraphs 1.E.1 through 1.E.7 or obtain permission +for the use of the work and the Project Gutenberg™ trademark as set +forth in paragraphs 1.E.8 or 1.E.9. + +*1.E.3.* If an individual Project Gutenberg™ electronic work is posted +with the permission of the copyright holder, your use and distribution +must comply with both paragraphs 1.E.1 through 1.E.7 and any additional +terms imposed by the copyright holder. Additional terms will be linked +to the Project Gutenberg™ License for all works posted with the +permission of the copyright holder found at the beginning of this work. + +*1.E.4.* Do not unlink or detach or remove the full Project Gutenberg™ +License terms from this work, or any files containing a part of this +work or any other work associated with Project Gutenberg™. + +*1.E.5.* Do not copy, display, perform, distribute or redistribute this +electronic work, or any part of this electronic work, without +prominently displaying the sentence set forth in paragraph 1.E.1 with +active links or immediate access to the full terms of the Project +Gutenberg™ License. + +*1.E.6.* You may convert to and distribute this work in any binary, +compressed, marked up, nonproprietary or proprietary form, including any +word processing or hypertext form. However, if you provide access to or +distribute copies of a Project Gutenberg™ work in a format other than +“Plain Vanilla ASCII” or other format used in the official version +posted on the official Project Gutenberg™ web site +(https://www.gutenberg.org), you must, at no additional cost, fee or +expense to the user, provide a copy, a means of exporting a copy, or a +means of obtaining a copy upon request, of the work in its original +“Plain Vanilla ASCII” or other form. Any alternate format must include +the full Project Gutenberg™ License as specified in paragraph 1.E.1. + +*1.E.7.* Do not charge a fee for access to, viewing, displaying, +performing, copying or distributing any Project Gutenberg™ works unless +you comply with paragraph 1.E.8 or 1.E.9. + +*1.E.8.* You may charge a reasonable fee for copies of or providing +access to or distributing Project Gutenberg™ electronic works provided +that + + - You pay a royalty fee of 20% of the gross profits you derive from + the use of Project Gutenberg™ works calculated using the method you + already use to calculate your applicable taxes. The fee is owed to + the owner of the Project Gutenberg™ trademark, but he has agreed to + donate royalties under this paragraph to the Project Gutenberg + Literary Archive Foundation. Royalty payments must be paid within 60 + days following each date on which you prepare (or are legally + required to prepare) your periodic tax returns. Royalty payments + should be clearly marked as such and sent to the Project Gutenberg + Literary Archive Foundation at the address specified in Section 4, + “Information about donations to the Project Gutenberg Literary + Archive Foundation.” + + - You provide a full refund of any money paid by a user who notifies + you in writing (or by e-mail) within 30 days of receipt that s/he + does not agree to the terms of the full Project Gutenberg™ License. + You must require such a user to return or destroy all copies of the + works possessed in a physical medium and discontinue all use of and + all access to other copies of Project Gutenberg™ works. + + - You provide, in accordance with paragraph 1.F.3, a full refund of + any money paid for a work or a replacement copy, if a defect in the + electronic work is discovered and reported to you within 90 days of + receipt of the work. + + - You comply with all other terms of this agreement for free + distribution of Project Gutenberg™ works. + + +*1.E.9.* If you wish to charge a fee or distribute a Project Gutenberg™ +electronic work or group of works on different terms than are set forth +in this agreement, you must obtain permission in writing from both the +Project Gutenberg Literary Archive Foundation and The Project Gutenberg +Trademark LLC, the owner of the Project Gutenberg™ trademark. Contact +the Foundation as set forth in Section 3. below. + +*1.F.* + +*1.F.1.* Project Gutenberg volunteers and employees expend considerable +effort to identify, do copyright research on, transcribe and proofread +works not protected by U.S. copyright law in creating the Project +Gutenberg™ collection. Despite these efforts, Project Gutenberg™ +electronic works, and the medium on which they may be stored, may +contain “Defects,” such as, but not limited to, incomplete, inaccurate +or corrupt data, transcription errors, a copyright or other intellectual +property infringement, a defective or damaged disk or other medium, a +computer virus, or computer codes that damage or cannot be read by your +equipment. + +*1.F.2.* LIMITED WARRANTY, DISCLAIMER OF DAMAGES – Except for the “Right +of Replacement or Refund” described in paragraph 1.F.3, the Project +Gutenberg Literary Archive Foundation, the owner of the Project +Gutenberg™ trademark, and any other party distributing a Project +Gutenberg™ electronic work under this agreement, disclaim all liability +to you for damages, costs and expenses, including legal fees. YOU AGREE +THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT LIABILITY, BREACH OF +WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE PROVIDED IN PARAGRAPH 1.F.3. +YOU AGREE THAT THE FOUNDATION, THE TRADEMARK OWNER, AND ANY DISTRIBUTOR +UNDER THIS AGREEMENT WILL NOT BE LIABLE TO YOU FOR ACTUAL, DIRECT, +INDIRECT, CONSEQUENTIAL, PUNITIVE OR INCIDENTAL DAMAGES EVEN IF YOU GIVE +NOTICE OF THE POSSIBILITY OF SUCH DAMAGE. + +*1.F.3.* LIMITED RIGHT OF REPLACEMENT OR REFUND – If you discover a +defect in this electronic work within 90 days of receiving it, you can +receive a refund of the money (if any) you paid for it by sending a +written explanation to the person you received the work from. If you +received the work on a physical medium, you must return the medium with +your written explanation. The person or entity that provided you with +the defective work may elect to provide a replacement copy in lieu of a +refund. If you received the work electronically, the person or entity +providing it to you may choose to give you a second opportunity to +receive the work electronically in lieu of a refund. If the second copy +is also defective, you may demand a refund in writing without further +opportunities to fix the problem. + +*1.F.4.* Except for the limited right of replacement or refund set forth +in paragraph 1.F.3, this work is provided to you ‘AS-IS,’ WITH NO OTHER +WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO +WARRANTIES OF MERCHANTABILITY OR FITNESS FOR ANY PURPOSE. + +*1.F.5.* Some states do not allow disclaimers of certain implied +warranties or the exclusion or limitation of certain types of damages. +If any disclaimer or limitation set forth in this agreement violates the +law of the state applicable to this agreement, the agreement shall be +interpreted to make the maximum disclaimer or limitation permitted by +the applicable state law. The invalidity or unenforceability of any +provision of this agreement shall not void the remaining provisions. + +*1.F.6.* INDEMNITY – You agree to indemnify and hold the Foundation, the +trademark owner, any agent or employee of the Foundation, anyone +providing copies of Project Gutenberg™ electronic works in accordance +with this agreement, and any volunteers associated with the production, +promotion and distribution of Project Gutenberg™ electronic works, +harmless from all liability, costs and expenses, including legal fees, +that arise directly or indirectly from any of the following which you do +or cause to occur: (a) distribution of this or any Project Gutenberg™ +work, (b) alteration, modification, or additions or deletions to any +Project Gutenberg™ work, and (c) any Defect you cause. + + + +Section 2. Information about the Mission of Project Gutenberg™ + + +Project Gutenberg™ is synonymous with the free distribution of +electronic works in formats readable by the widest variety of computers +including obsolete, old, middle-aged and new computers. It exists +because of the efforts of hundreds of volunteers and donations from +people in all walks of life. + +Volunteers and financial support to provide volunteers with the +assistance they need, is critical to reaching Project Gutenberg™’s goals +and ensuring that the Project Gutenberg™ collection will remain freely +available for generations to come. In 2001, the Project Gutenberg +Literary Archive Foundation was created to provide a secure and +permanent future for Project Gutenberg™ and future generations. To learn +more about the Project Gutenberg Literary Archive Foundation and how +your efforts and donations can help, see Sections 3 and 4 and the +Foundation web page at http://www.pglaf.org . + + + +Section 3. Information about the Project Gutenberg Literary Archive +Foundation + + +The Project Gutenberg Literary Archive Foundation is a non profit +501(c)(3) educational corporation organized under the laws of the state +of Mississippi and granted tax exempt status by the Internal Revenue +Service. The Foundation’s EIN or federal tax identification number is +64-6221541. Its 501(c)(3) letter is posted at +https://www.gutenberg.org/fundraising/pglaf . Contributions to the +Project Gutenberg Literary Archive Foundation are tax deductible to the +full extent permitted by U.S. federal laws and your state’s laws. + +The Foundation’s principal office is in Fairbanks, Alaska, with the +mailing address: PO Box 750175, Fairbanks, AK 99775, but its volunteers +and employees are scattered throughout numerous locations. Its business +office is located at 809 North 1500 West, Salt Lake City, UT 84116, +(801) 596-1887, email business@pglaf.org. Email contact links and up to +date contact information can be found at the Foundation’s web site and +official page at http://www.pglaf.org + +For additional contact information: + + Dr. Gregory B. Newby + Chief Executive and Director + gbnewby@pglaf.org + + + +Section 4. Information about Donations to the Project Gutenberg Literary +Archive Foundation + + +Project Gutenberg™ depends upon and cannot survive without wide spread +public support and donations to carry out its mission of increasing the +number of public domain and licensed works that can be freely +distributed in machine readable form accessible by the widest array of +equipment including outdated equipment. Many small donations ($1 to +$5,000) are particularly important to maintaining tax exempt status with +the IRS. + +The Foundation is committed to complying with the laws regulating +charities and charitable donations in all 50 states of the United +States. Compliance requirements are not uniform and it takes a +considerable effort, much paperwork and many fees to meet and keep up +with these requirements. We do not solicit donations in locations where +we have not received written confirmation of compliance. To SEND +DONATIONS or determine the status of compliance for any particular state +visit https://www.gutenberg.org/fundraising/donate + +While we cannot and do not solicit contributions from states where we +have not met the solicitation requirements, we know of no prohibition +against accepting unsolicited donations from donors in such states who +approach us with offers to donate. + +International donations are gratefully accepted, but we cannot make any +statements concerning tax treatment of donations received from outside +the United States. U.S. laws alone swamp our small staff. + +Please check the Project Gutenberg Web pages for current donation +methods and addresses. Donations are accepted in a number of other ways +including checks, online payments and credit card donations. To donate, +please visit: https://www.gutenberg.org/fundraising/donate + + + +Section 5. General Information About Project Gutenberg™ electronic +works. + + +Professor Michael S. Hart is the originator of the Project Gutenberg™ +concept of a library of electronic works that could be freely shared +with anyone. For thirty years, he produced and distributed Project +Gutenberg™ eBooks with only a loose network of volunteer support. + +Project Gutenberg™ eBooks are often created from several printed +editions, all of which are confirmed as not protected by copyright in +the U.S. unless a copyright notice is included. Thus, we do not +necessarily keep eBooks in compliance with any particular paper edition. + +Each eBook is in a subdirectory of the same number as the eBook’s eBook +number, often in several formats including plain vanilla ASCII, +compressed (zipped), HTML and others. + +Corrected _editions_ of our eBooks replace the old file and take over +the old filename and etext number. The replaced older file is renamed. +_Versions_ based on separate sources are treated as new eBooks receiving +new filenames and etext numbers. + +Most people start at our Web site which has the main PG search facility: + + https://www.gutenberg.org + +This Web site includes information about Project Gutenberg™, including +how to make donations to the Project Gutenberg Literary Archive +Foundation, how to help produce our new eBooks, and how to subscribe to +our email newsletter to hear about new eBooks. |