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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..d7b82bc --- /dev/null +++ b/.gitattributes @@ -0,0 +1,4 @@ +*.txt text eol=lf +*.htm text eol=lf +*.html text eol=lf +*.md text eol=lf diff --git a/LICENSE.txt b/LICENSE.txt new file mode 100644 index 0000000..6312041 --- /dev/null +++ b/LICENSE.txt @@ -0,0 +1,11 @@ +This eBook, including all associated images, markup, improvements, +metadata, and any other content or labor, has been confirmed to be +in the PUBLIC DOMAIN IN THE UNITED STATES. + +Procedures for determining public domain status are described in +the "Copyright How-To" at https://www.gutenberg.org. + +No investigation has been made concerning possible copyrights in +jurisdictions other than the United States. Anyone seeking to utilize +this eBook outside of the United States should confirm copyright +status under the laws that apply to them. diff --git a/README.md b/README.md new file mode 100644 index 0000000..c7364f8 --- /dev/null +++ b/README.md @@ -0,0 +1,2 @@ +Project Gutenberg (https://www.gutenberg.org) public repository for +eBook #62557 (https://www.gutenberg.org/ebooks/62557) diff --git a/old/62557-0.txt b/old/62557-0.txt deleted file mode 100644 index 07604c8..0000000 --- a/old/62557-0.txt +++ /dev/null @@ -1,1465 +0,0 @@ -The Project Gutenberg EBook of The Dominion Astrophysical Observatory, by -John Stanley Plaskett - -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 -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. - -Title: The Dominion Astrophysical Observatory - Victoria, B.C. - -Author: John Stanley Plaskett - -Release Date: July 4, 2020 [EBook #62557] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK DOMINION ASTROPHYSICAL OBSERVATORY, VICTORIA, B.C. *** - - - - -Produced by Andrew Sly, MFR, David E. Brown, and the Online -Distributed Proofreading Team at https://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - - - - - - - -[Illustration: _Frontispiece_--BUILDING AND DOME FROM SOUTH] - - - - - DEPARTMENT OF THE INTERIOR - - Hon. Charles Stewart Minister - W. W. Cory, C.M.G. Deputy Minister - - - The - Dominion Astrophysical - Observatory - - Victoria, B.C. - - A sketch of the development of astronomy - in Canada and of the founding of this observatory. - A description of the building and of the - mechanical and optical details of the telescope. An - account of the principal work of the institution. - - By - J. S. Plaskett, F.R.S. - - - Ottawa - F. A. ACLAND, - Printer to the King’s Most Excellent Majesty - 1923 - - - - -STAFF OF THE OBSERVATORY: - - - Director J. S. Plaskett, B.A., D.Sc., F.R.S.C., F.R.S. - Research Astronomer W. E. Harper, M.A. - Astronomer Reynold K. Young, Ph.D., F.R.S.C. - Astronomer H. H. Plaskett, B.A. - Secretary Miss H. R. Keay - Observing Assistant T. T. Hutchison, Esq. - - - - -THE DOMINION ASTROPHYSICAL OBSERVATORY - -VICTORIA, B.C. - -By J. S. PLASKETT, Director. - - - - -SECTION 1.--HISTORY AND CONSTRUCTION - - -Introduction - -This description of the observatory, its equipment and work has been -written by the director in response to a need, frequently expressed -by the numerous visitors to the institution, of a non-technical -account of the principles of the telescope and of the work of the -institution. This account will commence by a short historical sketch -of the beginnings of the undertaking followed by a description of the -observatory and telescope and concluded by a resume of its work. - - -Historical Sketch - -This observatory is a branch of the Department of the Interior -of the Federal Government, the department which has charge of -the administration of the western lands of the Dominion. In the -colonization of these lands, one of the obvious first needs was a -survey of the boundaries and subdivision into townships and sections. -This need led to the organization of a surveys branch of the department -and out of the necessity of accurate astronomical observations to -delimit the boundaries and define the position of the base lines -for subdivision work arose the astronomical branch. The first Chief -Astronomer of Canada, the late Dr. W. F. King, was a man of sterling -integrity and remarkable ability and to his genius must be ascribed in -large degree the present development of astronomy in Canada. As Chief -Astronomer and H. M. Commissioner of International Boundaries, he -early realized the need of an observatory for an initial meridian, for -housing and standardizing the instruments, and for some astronomical -research. He was successful in having the fine Dominion Observatory -erected on the Experimental Farm, Ottawa, in 1905 which housed the -Astronomical Branch, the staff of the International Boundary Surveys -and later the Geodetic Survey of Canada, of which he was the first -superintendent. - -The Dominion Observatory was equipped with a 15-inch refractor -provided with micrometer, photometer, solar and stellar cameras, -and spectrograph. The writer was entrusted with the work with this -telescope and the spectroscopic work especially was energetically -developed and helped, with the other activities of the institution, to -bring gratifying recognition from the scientific world. The need of a -larger aperture for extending this part of the work was soon realized -by the writer and was brought to the attention of the Government. -After some delays, owing to various circumstances, it was finally -decided early in 1913 to provide a large reflector for extending -the work. Enquiries were at once made, specifications prepared and -estimates obtained from prospective makers of the instrument. Contracts -were finally awarded in October 1913 to the John A. Brashear Co. of -Pittsburgh for the optical parts and to the Warner & Swasey Co. of -Cleveland for the mechanical parts of a 72-inch reflecting telescope. - - -Location - -It was necessary to know the location of the instrument before the -design of the mounting could be completed as the angle of the polar -axis depends upon the latitude of the site. When the new telescope -was first proposed there was no thought of locating elsewhere than at -the seat of government at Ottawa. However, upon further consideration -it was decided that the telescope should be located where, in Canada, -the best observing conditions prevailed. To determine this location -preliminary selection of five likely stations was made by the aid of -Sir Frederic Stupart, chief of the Meteorological Service from the -meteorological records. These stations, at Ottawa, at Medicine Hat, -at Banff, at Penticton, and at Victoria were occupied by Mr. W. E. -Harper, astronomer at Ottawa and the astronomical conditions were -observed by means of a 4.5-inch telescope. Victoria was unmistakably -superior in “seeing” or defining power, in low diurnal and seasonal -range of temperature and about equal so far as quantity of clear sky is -concerned. For such a large telescope as a 72-inch there could be no -question of the marked astronomical advantages of such a location, and -it was therefore decided to locate the telescope at Victoria. While the -observatory should not be in the city itself it should not be too far -away, not only on account of accessibility and facility in obtaining -supplies, but also the advantageous conditions of good seeing, low -diurnal range of temperature and small rainfall were confined to a -relatively small area near Victoria. An isolated monadnock called -locally Little Saanich Mountain but now named Observatory Hill, was -selected. This hill is about 7 miles north of Victoria and has a main -road and an interurban railway passing its base. It has an elevation of -730 feet, sufficient area around the summit for all necessary buildings -and was by far the most suitable site available. - - -Construction - -The Provincial Government had generously agreed to give $10,000 for the -purchase of a site and to build a road to the summit. This undertaking -was fully met and the road, splendidly located and constructed and -costing over $25,000, was completed in the spring of 1915. Contracts -for the construction of the telescope pier and the circular steel -walls of the building were awarded to a local firm and this work -was completed in 1916. The revolving dome with accessories for the -operation of the telescope was made by the Warner & Swasey Co., the -builders of the telescope mounting, and was completed and erected in -1916, thus making the building ready for the telescope. - -The design of the mounting was very carefully gone into by the Warner -& Swasey Co. in collaboration with the writer and was completed in the -autumn of 1914. Construction was at once begun and the mounting was -completed and temporarily erected at Cleveland in May 1916. It was then -shipped to Victoria and permanently erected in its building by November -1916. - -The order for the large disc for the 72-inch mirror and for an -auxiliary flat of 55 inches diameter for testing the 72-inch was given -to the St. Gobain Glass Works of Paris by the Jno. A. Brashear Co. -as soon as the contract was awarded. The 72-inch disc was cast and -annealed by June 1914 and was fortunately shipped at once without -waiting for the 55-inch disc. It left Antwerp only about a week before -war was declared and it was only by this small margin that Canada now -has a 72-inch telescope. Grinding and polishing were at once begun -but the lack of the large flat and other difficulties delayed the -completion and it was not until April 1918, about a year and a half -after the completion of the mounting, that the figuring was finally -completed and the telescope ready for work. Nevertheless, for an -undertaking of such magnitude the work was completed in record time, -four and a half years after the awarding of the contracts. - - - - -SECTION 2.--THE BUILDING AND DOME - - -The Observatory Building - -The building for housing a large reflecting telescope requires to -be of special design for the best results. It should not rise above -the shade temperature during the day and should rapidly assume and -follow the external temperature at night. Such materials as brick or -stone are obviously not suitable and all recent telescope buildings -are entirely of metallic construction in order to assume quickly the -night temperature, and of double-walled, ventilated type to prevent -overheating from the sun’s rays. The building for the 72-inch telescope -is entirely of steel construction, circular in form, 66 feet in -external diameter and with vertical walls 32 feet high. A view from -the south is given in the Frontispiece and from the north in Fig. 1, -showing the city of Victoria and the straits of Juan de Fuca in the -background. An external and internal covering of galvanized iron -separated by about 16 inches allows free circulation of air from a -peripheral opening at the base up through a similar double walled dome -and out of louvres at the top. The ground floor of Terrazo is laid -directly on the rock base and the observing floor 22 feet above this -is formed of steel girders and checkered steel plate. In the centre of -the ground floor rises the massive pier to support the telescope, of -reinforced concrete and symmetrical tapering form. The pier is actually -double, united below the observing floor by a massive reinforced arch -and extending above the floor as two piers (see Fig. 2) one for each -end of the polar axis. Temporary partitions on the ground floor provide -a dark room, sleeping room, and temporary office quarters. - -[Illustration: Fig. 1.--OBSERVATORY BUILDING FROM THE NORTH] - - -The Dome - -This circular steel building is capped by a circular plate supported by -massive girders on which is placed a curved railroad iron rail turned -and adjusted perfectly level and circular. The hemispherical dome turns -on this rail on 24 massive wheels mounted on roller bearings and is -rotated by an electric motor mechanism operated by reversing switches -on each side of the south pier. The framework of this dome, which is -66 feet in external diameter and about 38 feet high, the lower 5 feet -being cylindrical, consists essentially of a circular base to which -the bearing wheels are attached and two double, very deep and rigid -main ribs, one of which can be seen in Fig. 3, 16 feet apart in the -clear and extending parallel to each other entirely across the dome. -These are united 6 feet beyond the zenith by a cross girder and this -opening, which can be revolved to any azimuth and can be closed by -double motor operated shutters, enables the telescope to observe at any -part of the sky. Auxiliary circular ribs reaching from the base ring -up to the main ribs all around the dome except at the shutter opening, -form the support for the double steel covering of 12 inches separation. -This ventilating space is united through suitable weather guards with -the space between the building walls and forms the protection against -overheating by the sun in the day time. - - -Dome Accessories - -The shutter opening 16 feet wide and extending from the base of the -dome to 6 feet beyond the zenith is closed by a double shutter also -double walled and ventilated. Canvas screens mounted on tubes and -operated by motor can be run up from the base of the shutter opening, -this one being shown in Fig. 3, and down from the top so as to limit -the opening to the width of the tube of the telescope. These screens -are necessary when the wind is blowing to prevent shaking of the tube -and consequent jumping of the star image. For enabling the observer -to reach conveniently the upper end of the telescope tube in any -position a counterweighted elevating platform, moved up and down the -shutter opening by motor and drum with lifting cables is provided. -This platform is 20 feet long and 4 feet wide with a wing at each end, -extending inwards about 6 feet, on which the observer can stand and -can move it and himself by a hand wheel up to and partly encircling -the telescope tube. The platform and movable wings, which are well -shown in Fig. 3, can be brought to any desired height by an operating -switch at one side and can be reached by an auxiliary stairway from a -small stationary platform attached to the base ring of the dome. This -stationary platform is reached from the observing floor by a permanent -stairway moving with the dome and extending to a foot from the floor. -Platform wings and stairways are made safe for observers by guard and -hand rails 30 inches high. This moving platform, an essential accessory -for direct photography and other work at the principal focus of the -telescope, meets, in a more convenient and satisfactory manner than any -other previous device for the purpose, all the observing requirements -for work at the upper end of the tube. - - -Mechanism for Silvering - -In order to renew the silver coating on the upper surface of the -mirror, which is necessary about three times a year, mechanism has to -be provided for handling the mirror and its cell, the lower section of -the telescope tube, with ease and safety. The mirror weighs over 2 tons -and the cell 4 tons, so 6 tons have to be removed from and replaced -on the telescope tube. This is effected by means of the silvering -car, which can be seen at the left of Fig. 2, a massive framework of -structural steel rolling on four flanged wheels on flush tracks in -the observing floor. With the tube turned to a vertical position, the -car is rolled from its normal position at the east side of the dome -directly under the tube and a motor-operated screw-jack surmounted by -a triangular rocking arm can be brought up against the bottom of the -cell. On removing the attaching bolts, cell and mirror can be lowered -and rolled on the car to the east out of the way. The removal of 6 tons -from one side throws the telescope out of balance and so the outboard -end of the declination axis is supported by a counterweighted strut -run up through the floor and the upper end of the tube tied to rings -at the top of the dome. With a band of paraffined paper tied around -the edge of the mirror and a plug in the central hole, the silvering -solution can be poured on and evenly flowed over the surface by rocking -on a steel ball at the top of the jack-screw. When the silvering is -complete, cell and mirror are replaced in the reverse order and the -car rolled back out of the way. The operation takes about a day and is -performed with perfect safety and ease. - -[Illustration: Fig. 2.--TELESCOPE IN AVERAGE OBSERVING POSITION] - - - - -SECTION 3.--MECHANICAL PARTS OF TELESCOPE - - -Introduction - -It is useful, before describing the mechanical parts or mounting of -the telescope, to explain the difference between the two kinds of -telescope, refracting and reflecting, employed in astronomical work. -The refracting telescope is the most familiar type as the ordinary -spyglass or draw-tube telescope and the field or opera glass are all -refracting telescopes. The refracting telescope is so called because -the light from the distant object is refracted through a lens at the -outer end of the tube and forms an image of the object at the inner -end, just as a camera forms an image on the ground glass or film, and -this image is viewed and magnified by the eyepiece or ocular. The -reflecting telescope on the other hand has the upper or outer end -of the tube open and the light from the distant object is reflected -(hence the name) from a concave mirror at the lower end of the tube, -forming the image of the object at the top, where it can be viewed and -magnified by the ocular as in the refractor. - -Each type of telescope has its astronomical advantages and -disadvantages. The refractor is better suited for visual observations -such as the measurement of double stars and the study of planetary -detail and is less affected by temperature changes than the reflector. -On the other hand the reflector, on account of its perfect achromatism, -is the instrument par excellence for photographic observations, and, as -more than three-fourths of modern astronomical work is photographic, it -appears to be superseding the refractor. This advantage is increased -by the fact that the refractor has apparently reached the useful -limit in size and that it costs at least three times as much as a -reflector of the same aperture. Although each type of telescope has -its characteristic type of mounting for astronomical purposes, the -principles are the same for each and can probably be most easily -followed by describing the essential parts of the mounting of the -72-inch telescope. - - -The Telescope Tube - -The tube performs the important function of carrying in relatively -invariable position and adjustment the optical parts of the telescope. -The tube of the 72-inch telescope is 31 feet long, 7 feet 4 inches -outer diameter and weighs 15 tons. Its form and construction are well -shown in Figs. 2 and 3. It consists of the main or central section -A, Fig. 2 the lower section B which carries the main mirror and the -skeleton section C which carries the secondary mirrors. The central -section is a cylindrical steel casting heavily ribbed on the inside -about 6 feet high and weighs 7 tons. The lower section is securely -bolted to it through the flanges shown and with the mirror and its -supporting mechanism weighs about 6 tons. The upper skeleton section -is built up of structural steel, 3 inch I beams, firmly braced and -rivetted together in the manner shown in the figures. A special -feature of this skeleton tube, making it more rigid than any previous -design, consists of the diagonal tension rods in each rectangular -compartment screwed up each to a tension of about 2,000 pounds, so -that the whole tube is under tension in every position. This stiffness -is essential for the proper performance of the optical parts, as the -principal and secondary mirrors at bottom and top of tube respectively -should occupy the same relative positions in whatever direction the -tube is pointed. - - -The Declination Axis - -The telescope tube is firmly screwed at right angles to the flanged end -of a massive shaft 16 inches in diameter, called the declination axis, -extending through the cubical section D of the polar axis NDS, Fig. 2, -through the declination sleeve E into the housing F. This declination -axis is rotated, carrying the tube with it, on ball bearings in D and -F, this rotation being effected by an electric motor with reduction -mechanism, gearing into a large spur gear attached to the end of the -declination axis, the whole being concealed within the declination -housing F. Hence the tube can be turned at the rate of 45 degrees to -the minute to any required position up or down, north or south. The -position in the sky, the declination, corresponding to latitude on the -earth, is read on a large circle graduated into degrees within F and -subdivided into 5 minute intervals on the small auxiliary circle H. - - -The Polar Axis - -As positions north or south are given by turning the tube on the -declination axis, so positions east or west are given by rotation on -the polar axis, so called because it points to the pole of the heavens -and is exactly parallel to the axis of the earth. The Polar axis NDS -Fig. 2, which is 21 feet long and weighs 9·5 tons, is built up of -three steel castings, a central cubical section D and two conical end -sections, all securely bolted together and turning in ball bearings -on its ends. The upper, north, bearing is carried in an adjustable -pillow block, by which the final parallelism with the earth’s axis is -obtained, bolted on the curved cement pier shown at the left or north -in Figs. 2 and 3. The lower, south, bearing is carried in a massive -cast iron pedestal bolted to the south cement pier. The polar axis is -rotated on these bearings, also at the rate of 45 degrees per minute, -carrying the declination axis and tube with it to any position east or -west in the sky by an electric motor and reduction gearing concealed -within the south pedestal. The position east or west in the sky, the -right ascension as it is called corresponding to longitude on the -earth, is read by means of a graduated circle shown above G, Fig. 2, -which is divided into 24 hours and each hour into single minutes. While -longitudes on the earth are occasionally expressed as so many hours -and minutes east or west of Greenwich, right ascensions in the sky are -almost invariably given in hours and minutes rather than degrees. - -[Illustration: Fig. 3.--TELESCOPE FROM THE WEST] - - -The Driving Clock - -It is evident, by rotation of the telescope on the declination and -polar axes by means of the quick-motion motors, that the tube can be -pointed in any direction in the sky, towards any star. But owing to the -rotation of the earth on its axis from west to east, which is the cause -of the apparent motion of sun, moon and stars from east to west, the -telescope will be quickly carried eastward of the star which will only -remain for an instant in the field. - -The mechanism by which the rotation of the earth is compensated for -is called the driving clock and is contained in the case L, Fig. 2, -at the north side of the south pier. In the lower half of the case a -governor similar to the governor of a steam engine is driven once per -second by a train of gears in the upper section actuated by a weight -of 300 pounds below the floor. If the speed of the governor tends to -increase the balls raise by centrifugal force and bring increased -friction to bear thus reducing the speed to normal while if the speed -tends to decrease, the balls drop and reduced friction quickly allows -it to accelerate to normal speed. A shaft with a coarse screw thread -on it, called technically a “worm” and situated at the top of the -case, is driven by intermediate gearing from the governor at the -rate of one revolution every two minutes. The thread on this shaft -engages into teeth cut in the worm wheel G, Fig. 2, which is 9 feet in -diameter. As there are 720 teeth very accurately spaced in this worm -wheel, it is driven around by the worm in 2 × 720 = 1,440 minutes, 24 -hours, the same rate as the earth. This worm wheel, normally loose -on the polar axis on which it turns on ball bearings, allowing the -axis to be moved freely to any position, can be rigidly clamped to it -by pressing a button. When this is done, it will evidently turn the -polar axis and hence the tube at the same rate as the earth but in the -opposite direction, on an axis parallel to the axis of the earth, thus -exactly compensating for the rotation of the earth. Hence any star -at which the telescope is pointed will automatically remain central -in the field. Owing to the great magnification all this mechanism -requires the highest grade of workmanship, else there will be wandering -of the image, a most annoying and troublesome defect. Few telescopes -are entirely free from periodic error and that the 72-inch drives -so regularly and smoothly is a great advantage and evidence of the -perfection of workmanship throughout. - - -Electric Motions - -It has already been described how the telescope can be moved by motors -north or south and east or west at the rate of 45 degrees per minute. -These motors are operated from small switchboards on each side of -the south pier, the one at the west being seen in Figs. 2 and 3. The -left-hand reversing switch moves the telescope east or west, the -centre switch north or south and the right-hand switch revolves the -dome east or west. In addition to these quick motions of the telescope -for rapidly bringing it to the approximate position, much finer and -slower motions are required for bringing the image exactly central and -for guiding. These slow motions are also operated by electric motors -actuated by two small aluminium switchboards attached by flexible -cables to the top and bottom of the tube. These switchboards can be -carried in the hands of the observer or rested on the observing -ladder. Pressure on suitable buttons moves the telescope north or -south, east or west at either one of two different speeds, a speed of -one revolution in 36 hours for centering the image and a speed of one -revolution in 30 days for guiding, correcting for slight irregularities -due to air disturbance or other causes. Although these speeds may seem -excessively slow, the motion of the image even with the monthly rate -is at once evident on pressing the button and faster speeds would make -accurate guiding difficult. In addition to the two quick and two slow -motion motors there are two clamping motors and one for automatically -rewinding the clock weight, seven in all. These with the three motors -operating the dome are all continuous current motors which can be -started and reversed more readily and have greater initial torque than -alternating motors. Each motor is supplied with an automatic control, -so that all that is necessary is to throw the switch or press the -button to start or reverse. Current is supplied by a motor generator -set on the ground floor. - - -Method of Operation - -A description of the method of setting upon the required star, when, -for example, photographing the spectra of the stars, will help to make -the operation of the telescope more clearly understood. It is easily -possible to pull the telescope around by hand to the required star -identified by eye among the constellations. Although the moving parts -of the telescope weigh nearly 45 tons, so perfect are the ball bearings -in which it turns that a weight of 3 pounds at the upper end of the -tube is sufficient to set it in motion. However the settings can be -much more quickly and certainly made by turning the telescope to the -right ascension and declination of the star by the electrical motions. -A programme of the stars to be observed with their right ascensions and -declinations is prepared beforehand. The observing assistant stands -beside the small switchboard on the south pier and rapidly moves the -telescope east or west and north or south until the indexes on the -graduated circles point to the tabulated positions, while the dome can -be turned to the required position at the same time by means of the -third operating switch. By pressing two buttons the telescope is then -firmly clamped and the driving clock starts the telescope automatically -following the star. In the meantime the observer has inserted the -plate holder in the spectrograph and drawn the slide and by means of -the aluminium switchboard brings the star, which is generally near the -centre, exactly to the centre of the finder, when it will be visible on -the slit of the spectrograph through a guiding eyepiece and can quickly -be brought central and the exposure commenced. The time required from -the end of one exposure to the beginning of the next, unless the stars -are far apart in the sky, does not generally exceed two minutes, a -shorter time than usually required for even quite small telescopes. -This rapid operation is due to special care in design and construction -and markedly increases the efficiency and capacity of the instrument. - - -Special Features of the Mounting - -The mounting of the 72-inch telescope has several new features not -hitherto used and sets a new standard for convenience and accuracy of -operation. The observatory is much indebted to the Warner & Swasey Co., -who have made most of the large mountings in America, for the spirit in -which they undertook and carried through this work. Their sole object -was to produce the best possible mounting regardless of cost and no -suggestion of the writer looking to improvement was refused. To Mr. -Swasey, the president, are due many of the original features of the -mounting and the beauty and harmony of the design, while Mr. Burrell, -the works manager, is responsible for the simplification of the -mechanism and the beautiful co-ordination of the details. No greater -testimony to the perfection of design and construction can be given -than to say that after five years use there is no feature the director -would wish changed, and no single defect of construction has been -revealed. - -It may be of interest to note the principal improvements in this -mounting. - -1. All parts of the sky can be readily reached. This is not possible -with all types of reflecting telescopes. - -2. The elimination of cylindrical bearings with cumbrous -friction-relieving devices, formerly considered necessary for -maintaining collimation and adjustment on declination and polar -axes, and the use of ball bearings for both friction-relieving and -collimating purposes has resulted in remarkable ease of movement of the -telescope. - -3. Freedom from periodic or other errors in driving and smoothness and -freedom from “backlash” in slow motions. - -4. Ease, speed and accuracy with which settings can be made due to -careful design and original features in setting motors and setting -circles. - -5. Great stiffness of tube and improvements in method of attaching and -changing secondary mirrors. - -6. Beauty and harmony of design and appearance. - - - - -SECTION 4.--OPTICAL PARTS AND SPECTROGRAPHS - - -The Principal Mirror - -The great mirror is composed of hard plate glass cast in one piece and -after annealing, ground and polished to the correct shape. As received -from the St. Gobain Co., the disc was 73·5 inches diameter, over 13 -inches thick with a central hole about 6 inches diameter and weighed -nearly 5,000 pounds. It was first of all ground truly circular to a -diameter of 73 inches and flat on both sides to a thickness of slightly -over 12 inches, while the central hole was enlarged to 10 inches. When -the back was polished approximately flat, the disc was seen to be a -beautiful specimen of the glass makers art, homogeneous and almost -entirely free from bubbles or other defects. - -[Illustration: Fig. 4.--PHOTOGRAPH OF RING NEBULA IN LYRA - -(_Enlarged 8 diameters_)] - -It was now ready for the second stage of the operation the grinding -of the correct shape for the upper reflecting surface. In order to -bring the light of a star to an accurate focus this surface must -be a paraboloid of revolution, the same kind of curve given to the -reflectors of search lights or automobile headlights. The curve for -this reflector of 30 feet focus is very nearly a section of a sphere of -60 feet radius, within one-thousandth of an inch, and consequently -would nearly fit a huge globe 120 feet in diameter. The upper surface -of the disc was fine ground and polished to this spherical surface and -was then ready for the final stage, the “figuring” a continuation of -the polishing process until the centre is deepened about a thousandth -of an inch and the surface becomes accurately paraboloidal. This -“figuring,” an exceedingly delicate and difficult process especially -over such a large surface as the 72-inch, with the added difficulty of -a central hole, occupied about two years and was not completed until -nearly a year and a half after the mounting was ready. When it is -remembered, however, that the surface nowhere deviates from the true -theoretical form more than one four-hundred-thousandth of an inch and -that if one part is accidentally polished too deep, the whole surface -has again to be brought down to this level, the exceeding delicacy of -the operation is evident and the time taken not excessive. - -Accurate quantitative tests showed that the final figure is of the -highest order of accuracy and this is further clearly shown by the -practical test of direct photographs at the principal focus. Figure -4, a six fold enlargement of a photograph at the principal focus, of -the Ring Nebula in Lyra shows how sharp and small are the star images. -Actual measurement on the original negative gives a minimum diameter -of two one-thousandths of an inch equivalent to only a second of arc -at the focus. As the images are enlarged considerably by unsteadiness -of the air and errors in guiding the star light reflected from the -whole surface of the mirror is collected into a little disc less than a -thousandth of an inch in diameter indicating the extraordinary accuracy -of the reflecting surface. Mr. J. B. McDowell, head of the firm since -Dr. Brashear’s death, and Mr. Fred Hegemann, his chief optician, are -to be highly congratulated on the perfection of figure obtained under -specially difficult circumstances. Further the fine rendering of the -detail in the ring and the strength of the two bands in the interior -indicate not only perfect figure but exceptionally high polish. - - -Mounting of Mirror - -This mirror, to maintain its accuracy, not only requires careful -mounting in its cell but also protection against temperature changes. -Even though 12 inches thick it would bend under its own weight of 4,300 -lbs. sufficiently to affect the figure and consequently it is supported -in the cell by a specially counterweighted lever system so that it is -equably supported at twelve points and there is no tendency to bend. -A similar lever support system around the edge prevents distortion -due to constraint when it is tipped from the horizontal position at -different positions of the tube. Temperature changes can produce much -greater distortion than flexure but Victoria has the advantage of very -low diurnal range and the temperature change around the mirror is made -very small by a lagging of cotton felt about 2 inches thick all round -the sides of the closed section of the tube, laced on with a duck -cover (compare Fig. 3 with Fig. 2) and an equal thickness below and -around the edge of the mirror. By this lagging the temperature rise in -the day-time is only about half a degree while the dome temperature -increases five degrees, hence the figure of the mirror remains good -whatever the temperature changes outside. - - -The Principal Focus - -As already indicated, the principal mirror when used alone forms an -image of the star 30 feet above, at the centre of the upper end of -the tube, and an eyepiece could be placed there for visual work or a -photographic plate for direct photographs of nebulae, etc. However, it -is generally more convenient to use a flat mirror at 45° forming the -image at the side of the tube for photographs and so the telescope is -only used in this form with a small spectrograph for the ultra-violet -region of star spectra. The course of the parallel beam of light from -the star to its image on the slit of the spectrograph is graphically -shown in Fig. 5 A and also its passage through the slit prisms and -lenses of the spectrograph. The position of the star image on the slit -of the spectrograph can be observed by a guiding telescope extending -to the edge of the tube and can be kept central by the portable -aluminium switchboard already described. The elevating platform is of -course used in work in this position. - - -The Newtonian Arrangement - -For direct photography or visual observations at the focus of the -72-inch mirror, the reflected cone of star light from the mirror B, -Fig. 5, is intercepted by a plane mirror also silvered on the front -surface, 19·5 inches diameter and 3·25 inches thick placed at 45°. This -form of reflecting telescope was first used by Newton, hence the name. -The focus is then formed, as shown, at the side of the tube, and if a -plate is placed there and accurately guided by small eyepieces with -cross wires, photographs of any desired small region in the sky can be -obtained, Fig. 4 being made in this position, or visual observations -may be made. The oculars can easily be reached from the observing -platform for any position of the telescope. - - -The Cassegrain Arrangement - -The most generally useful arrangement of the 72-inch telescope is, -however, the Cassegrain form, so called from the French astronomer who -first used it. About 7 feet below the focus, the conical reflected -pencil from the 72-inch mirror is intercepted by a convex mirror of -the same size as the Newtonian and of about 10 feet focal length as -seen in C, Fig. 5, and also shown in Fig. 2 and 3. This mirror turns -the light downward and, after passing through the central hole, forms -the image of the star about two feet below the mirror surface on the -slit of the spectrograph or on a visual attachment as shown. The -significant property of this combination is that the focal length is -increased from 30 to 108 feet without changing the tube length in a -somewhat similar manner to the action of a telephoto lens. It has the -same size of image and magnifying power as a refractor with a tube 108 -feet long and has the decided advantage of a much shorter tube and -smaller dome. Observations with this arrangement are made at the lower -end of the tube from the observing floor and with much greater ease -and convenience than at the upper end. Changes from the Cassegrain to -the Newtonian or Principal Focus arrangements are readily effected by -a device due to the genius of Mr. Swasey whereby only the mirrors and -attaching tubes require to be handled, instead of the whole upper end -of the tube as in previous reflectors. - -[Illustration: Fig. 5.--COURSE OF LIGHT IN TELESCOPE FROM STAR TO FOCUS] - - -Accessory Optical Parts - -A full set of eyepieces giving magnifying powers from 120 to 5,000 -diameters and a complete double-slide plate holder with guiding -eyepieces for direct photography at the Newtonian focus are provided. -In addition there is a visual attachment shown in diagram C, Fig. 5, -which enables the telescope to be used visually at the Cassegrain focus -without removing the spectrograph. There are three finders attached -to the telescope tube for picking up and centering the stars. Two of -4 inch aperture and 5 feet focus, of power about 50, one north, one -south on the tube, and a long focus tubeless finder with a lens of 7 -inch aperture and 30 feet focus at the top of the telescope tube and an -ocular of power 200 at the bottom. - - -The Spectrographs - -Most of the astronomical work with the 72-inch telescope is -spectroscopic, photographing the spectra of the stars, and so a -description of the principles and operation of spectrographs is -desirable. Stellar spectrographs have evolved into certain definite -forms and the two spectrographs for the 72-inch telescope are examples -of the most recent types. In essence a spectrograph consists of a -narrow slit, one or two-thousandths of an inch wide, on which the -star light is focussed. That passing through the slit falls on the -collimator lens which makes it parallel and then on a prism or prisms, -triangular shaped pieces of glass which change the direction of the -light and decompose it, breaking it up into its constituent rainbow -colours. The spectrum, as it is called, is focussed by a camera lens on -a photographic plate or can be viewed by a small telescope if desired. -The course of the star light from the slit through collimator, prism -and camera lens to the plate is shown in C, Fig. 5, while a view of the -Cassegrain spectrograph showing the interior mechanism and accessories -is given in Fig. 6. The part of the spectrum photographed is usually -only the blue and violet region to which the ordinary plate is most -sensitive, and obviously no colours appear on the negative but only a -narrow dark strip which is crossed by light or dark lines. It is from -the number and position of these lines that we obtain such a remarkable -amount of information about the physical and chemical constitution, the -temperature, motion and distance of the stars. The length of the star -spectrum photographed with one prism is about one and a third inches, -twice and three times that with two and three prisms. Its width is -about one-hundredth of an inch and in order to make it this wide the -star image has to be moved back and forward along the slit. The length -of spectrum with the ultra-violet spectrograph, which only differs from -the other in the prisms and lenses allowing the spectrum below the -violet to pass, is about one inch. A photograph of the spectrum of iron -or brass is made beside the star spectrum to serve as a standard to -determine the positions of the star lines. - -[Illustration: Fig. 6.--STELLAR SPECTROGRAPH ARRANGED FOR USE WITH ONE -PRISM - -(TEMPERATURE CASE REMOVED)] - - -Method of Use - -Every terrestrial element gives groups of lines in certain positions -in the spectrum and if we find similar groups in the star spectrum -we are sure this element is present in the star. Further if we find -these lines are displaced to red or violet of their normal position -we know that the star is receding from or approaching to us. With -the one-prism spectrograph a speed of one mile per second means a -displacement of the lines of one thirty-thousandth of an inch. Thus -if the lines are shifted to the violet by a thousandth of an inch, -the star is approaching the earth with a speed of 30 miles a second. -These displacements are accurately measured by a microscope and the -measurement of the radial velocities of the stars is one of the main -researches of this observatory. Obviously with such small displacements -to be measured the greatest care must be taken to avoid all sources -of error. The spectrograph must be exceptionally rigid to avoid -differential bending as it moves with the telescope. As change of -temperature can produce spurious shifts of the lines, the temperature -must be kept as constant as possible, this being effected here by -a very accurate electrical thermostatic device called the Calendar -Recorder which maintains the temperature constant to one-hundredth of -a degree. The optical parts must be of the highest quality to give -perfect definition to the spectrum lines and many other precautions -must be taken if accurate work is desired. The spectrographs of the -72-inch telescope have unequalled defining power and are the last word -in convenience of manipulation and accuracy of work. - -Owing to the faintness of the star light and to its being spread out -into a spectrum a considerable time is required to photograph the -spectrum of a star, about 20 minutes for the sixth magnitude, the limit -of visibility to the unaided eye, when photographed with one prism, -while three prisms will take nearly five times as long. Hence the -necessity and use of large telescopes is not to get high magnifying -power but to collect sufficient light from the fainter stars to enable -their spectra to be photographed or other observations made. - - - - -SECTION 5.--THE WORK OF THE TELESCOPE - - -Prevalent Misconceptions - -The general idea of an astronomer’s work, as gathered from the -questions and remarks of visitors, is that he sits at the eyepiece of -the telescope sweeping the heavens in a search for new planets, comets -or stars. The absolute futility of such a use of the telescope is -evident when it is realized that the main field of the 72-inch covers -only about one hundred-millionth of the sky and if only five seconds -was required to examine each field it would take more than a lifetime -to go over the whole sky once. A second misconception is the idea that -large telescopes are used for visual observations of the planets with -special reference to their habitability. No work is being attempted -at this or other large observatories on planetary detail for which -about an 18-inch refractor gives the best results and such a large -telescope as the 72-inch is quite unsuited. All scientific observations -with the 72-inch are made photographically and it is only arranged for -visual use on Saturday evenings when for two hours visitors are allowed -to observe the heavenly bodies. A third misconception is that the -astronomer only works at night. However true this idea may have been -in the days of visual observations when the measurements were made at -the eyepiece, there is certainly now, when photography is so generally -applied, more day than night work in astronomy. Besides the advantages -of permanency, accuracy of measurement and power of recording objects -beyond the range of the keenest eyesight, the photographic method has -the further great advantage that an hour’s exposure may give sufficient -material for several days’ measurement and discussion. - - -Spectroscopic Work - -As already indicated most of the work with the 72-inch telescope -is spectroscopic, but as also indicated modern spectroscopic -investigations cover so wide a range of research that the actual work -of the observatory is very varied. By aid of suitable spectrographs -attached to a large telescope we can measure the speed of the stars -towards or from us, their radial velocity as it is termed. We can -discover double stars too close ever to be seen double in any telescope -and we can determine the manner in which they revolve around one -another and their distance apart and mass. From the spectra of the -stars we can determine their absolute brightness as compared with the -sun and their parallax or distance. The chemical elements present in -the outer atmospheres of the stars can be determined and the pressure -in these atmospheres. The measurement of temperatures and other -physical conditions in the stars by means of the spectroscope is now -an accomplished fact and one of the most recent developments of the -spectroscopic work here has been to provide evidence of the truth of -a theory of atomic structure and to show that the atomic constants in -the enormous furnaces of the stars are the same as on the earth. Such -a catalogue of information, obtained from an investigation of the mere -quality of the light from stars so faint as to be quite invisible to -the unaided eye and so distant that it may take thousands of years -to travel to us, is sufficiently comprehensive to be treated in more -detail. - - -Radial Velocities - -When the 72-inch telescope was in course of design and construction, -one of the greatest needs in astronomical work was increased data in -regard to the radial velocities of the stars. Although the telescope -was so designed as to be suitable for all kinds of observational -work, special attention was devoted to the spectroscopic end. After -consultation with the most prominent astronomers an observing programme -of about 800 stars whose “proper” or cross motions across the sky were -accurately known but whose radial velocities had not been determined, -was prepared and spectroscopic observations of the stars on this -programme were commenced as soon as the telescope was completed in -May 1918. After slightly over three years’ work, observation and -measurement were completed and Vol. II, No. 1 of the observatory -publications, “The Radial Velocities of 594 Stars,” was published early -in 1922. As hitherto the radial velocities of only about 2,000 stars -had been obtained, this work was a considerable addition to existing -data about the motions of the stars and will be of great use in -extending our knowledge of the structure and motions of the universe. -A second programme of 1,500 stars has been prepared but owing to other -intervening observational work, not much has yet been done on this new -programme. - -One of the auxiliary programmes undertaken and nearly completed since -the first programme is the determination of the radial velocities of a -very interesting but limited class of stars, the highest temperature -stars known, the O-type stars. The radial velocities and other -interesting data about 50 of these stars have been completed. - - -Spectroscopic Double Stars - -In the measurement of the radial velocity of the 800 stars on the -first programme it was found that in about 180 stars successive plates -did not give constant velocities, the stars at one time approaching -at another receding from us. This phenomenon is practically certain -proof that we are measuring the velocity of a star revolving around an -invisible companion and such stars are generally called spectroscopic -binaries to distinguish them from visual binaries which can be seen -double in the telescope. Over 200 spectroscopic binaries have been -discovered at this observatory as compared with about 700 discovered -elsewhere, again a considerable addition. In about 20 of these -binaries, observations were continued until the period of revolution, -the form of the orbit, the separation of the two stars and in some -cases, their masses were determined. In a particular class of -spectroscopic binaries, the eclipsing variables, which allow from the -combination of spectroscopic and photometric measurements the absolute -dimensions to be obtained, we were able to determine the separation of -the two stars, their diameters, densities, masses and brightnesses and -the probable distances. Such complete information has been obtained -here about seven systems, while only seven other systems have been -determined elsewhere. - - -Absolute Magnitude and Distance - -A new application of spectroscopic methods is to the determination of -the total brightness of the stars as compared with the sun and their -distance or “spectroscopic parallax” as it is called. This depends not -on the positions but on the relative intensity or strength of the lines -in the spectra of the stars and has only been developed in the last -three or four years. The absolute magnitude and spectroscopic parallax -of about 800 stars is now nearly completed and will soon be published -while as a side line the radial velocities of 125 more stars have been -determined. - - -Physical Conditions in the Stars - -The spectrographs have also been used by one member of the staff in -the determination of the physical and chemical conditions in stellar -atmospheres, a new and difficult problem but one which promises not -only very valuable additions to our knowledge of the constitution of -the stars but may also lead to economic applications of the greatest -importance. A new method depending upon the use of a wedge of dark -glass has been applied to determining the distribution of energy in the -different parts of the spectrum of the stars and to measuring their -temperatures, while an application of the same methods to individual -lines may lead to a great increase in our knowledge of conditions in -the stars. A special investigation of three of the high temperature -O-type stars referred to above has proved the existence in the spectra -of these stars of lines predicted as present from purely theoretical -conditions but never previously identified and has thus remarkably -verified a theory of the structure of the atom. The measurement of the -wave lengths of these hitherto unknown lines has led to an important -independent determination of the fundamental constants of atomic -structure and the dimensions of the atom and has shown that these -constants and dimensions are the same in the tremendous furnaces of -the stars as in our terrestrial laboratories, a verification of the -homogeneity of matter and the uniformity of physical laws throughout -the universe. Further interesting results from this investigation -are the application of a new theory of ionization with the probable -relative abundance of the elements to an independent determination of -the temperature of these stars. - - -Other Investigations - -Direct photographs have been made of some nebulae and clusters but -this work is not being definitely followed at present. Investigations -into the phenomena accompanying some short period binaries have been -made and into the behaviour of the two strong calcium lines H and K -in the spectra of the high temperature stars from which interesting -and valuable results are expected. Since the observatory commenced -work two bright novae or new stars have appeared, which have been -fully observed spectroscopically here and the results discussed. The -plates of the nova in Aquila have been loaned to the observatory at the -University of Cambridge, England, for fuller discussion and analysis. - - -Value of Astronomical Work - -This brief sketch of the work of the observatory naturally leads to -the question frequently asked of astronomers:--What use is the work -done at observatories and what practical value can a knowledge of the -stars have in everyday life? While astronomy has obvious practical -applications to navigation and surveying yet nine-tenths of modern -astronomical research is devoted to the more or less abstract question -of the constitution and motion of the stars and the structure of the -universe. Indeed most physical and chemical as well as astronomical -research is undertaken for the purpose of increasing our knowledge -and of investigating the secrets and laws of nature and has generally -no direct practical economic application. But it is now generally -recognized by the layman as well as the scientist that without abstract -there can be no applied science and that all the great economic and -industrial applications of science have had to be preceded by the -abstract and apparently non-practical investigations of pure science. -The Great War perhaps made more evident than ever before the absolute -dependence of applied science upon the unselfish and abstract work of -pure science. - - -Economic Value - -In view of past experience in science it would hence be a rash -prediction to assert that the investigation of the conditions in -distant stars can have no practical application upon earth. It may be -of interest to point out one possible application of astrophysical -research. - -It is generally agreed that one of the most important economic -problems of the not far distant future will be the provision of -sources of energy to replace our rapidly depleting supplies of coal -and oil. It appears now that the most probable solution of this -problem will consist in the development of some method for utilizing -the inexhaustible stores of energy contained in the atoms of matter. -Modern research on conditions in the stars has made it practically -certain that the enormous supply of energy, which has been radiated -into space for aeons of time from these bodies, can only be maintained -undiminished by the energy released by the transformation of atoms -in the interior of the stars, where conditions of temperature and -pressure prevail at present unattainable in terrestrial laboratories. -The most hopeful line of attack upon this tremendously important -economic problem hence seems to lie in the systematic astrophysical -investigation of conditions in the stars supplemented by physical and -chemical researches on the structure of the atom. - - -Ethical Value - -While astronomers and scientific men generally fully realize the value -of the practical applications of science, their main purpose is the -search for truth and the extension of our knowledge of nature. While it -is possible that investigation of the stars may have immense economic -value, it is certain that it has tremendous ethical value giving us a -clearer knowledge of the laws of nature and of our relations to the -wonders of creation. Astronomy is the oldest and in many respects the -most important of the sciences and its study, through the ages has -been one of the most elevating influences on human character. Poincaré -has well said that if the earth had been so continuously covered with -clouds that the heavenly bodies could not be seen, mankind would still -be in a primitive state and under the domain of superstition. The main -superiority of modern over ancient civilization does not consist in the -greater abundance of the necessities and luxuries of life, although -this is undoubtedly due primarily to scientific research, but to the -elevating influences of the truer conceptions of nature made possible -by the abstract study of astronomy and other sciences. - -It has been truly said that the degree of civilization of a country may -be judged by the support it gives to the study of astronomy. By the -establishment and maintenance of the Dominion Observatory at Ottawa -and of the Dominion Astrophysical Observatory at Victoria with the -second largest telescope in the world, Canada has a just claim on this -criterion to the favourable estimation of the scientific world. - - VICTORIA, B.C., - May, 1923. - - - - -TRANSCRIBER’S NOTES: - - - Italicized text is surrounded by underscores: _italics_. - - Obvious typographical errors have been corrected. - - - - - -End of the Project Gutenberg EBook of The Dominion Astrophysical Observatory, by -John Stanley Plaskett - -*** END OF THIS PROJECT GUTENBERG EBOOK DOMINION ASTROPHYSICAL OBSERVATORY, VICTORIA, B.C. *** - -***** This file should be named 62557-0.txt or 62557-0.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/6/2/5/5/62557/ - -Produced by Andrew Sly, MFR, David E. 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S. Plaskett. - </title> -<link rel="coverpage" href="images/cover.jpg" /> - <style type="text/css"> - -body { - margin-left: 10%; - margin-right: 10%; -} - - h1,h2,h3 { - text-align: center; - clear: both; -} - -p { - margin-top: .51em; - text-align: justify; - margin-bottom: .49em; -} - - -div.chapter {page-break-before: always;} -h2.nobreak {page-break-before: avoid;} - -div.titlepage {text-align: center; page-break-before: always; page-break-after: always;} -div.titlepage p {text-align: center; font-weight: bold; line-height: 1.5; margin-top: 2em;} - - -hr { - width: 33%; - margin-top: 2em; - margin-bottom: 2em; - margin-left: 33.5%; - margin-right: 33.5%; - clear: both; -} - - -hr.chap {width: 65%; margin-left: 17.5%; margin-right: 17.5%;} -hr.tb {width: 45%; margin-left: 27.5%; margin-right: 27.5%;} - - - - -table { - margin-left: auto; - margin-right: auto; -} - - .tdr {text-align: right;} - - -.pagenum { - position: absolute; - left: 92%; - font-size: smaller; - text-align: right; -} - -.blockquot {text-align: justify; margin-left: 30%; margin-right: 30%;} - -.bb {border-bottom: double 5px;} - - - - -.center {text-align: center;} - - -.ph1 {text-align: center; font-size: xx-large; font-weight: bold;} -.ph2 {text-align: center; font-size: large; font-weight: bold;} -.gap {margin-left: 3.2em;} -.gap2 {margin-left: .5em;} -.caption {font-weight: bold; text-align: center;} - -.large {font-size: 125%;} - -.figcenter { - margin: auto; - text-align: center; - margin-top: 2em; -} - -p.drop-cap { - text-indent: -0.2em; -} - - -p.drop-cap:first-letter -{ - float: left; - margin: 0.2em 0.1em 0em 0em; - font-size: 250%; - line-height:0.55em; - text-indent: 0em; -} -@media handheld -{ - p.drop-cap { - text-indent: 0em; - } - p.drop-cap:first-letter - { - float: none; - margin: 0; - font-size: 100%; - } -} - - -.transnote {background-color: #E6E6FA; - color: black; - font-size:smaller; - padding:0.5em; - margin-bottom:5em; - font-family:sans-serif, serif; } - </style> - </head> -<body> - - -<pre> - -The Project Gutenberg EBook of The Dominion Astrophysical Observatory, by -John Stanley Plaskett - -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 -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. - -Title: The Dominion Astrophysical Observatory - Victoria, B.C. - -Author: John Stanley Plaskett - -Release Date: July 4, 2020 [EBook #62557] - -Language: English - -Character set encoding: ISO-8859-1 - -*** START OF THIS PROJECT GUTENBERG EBOOK DOMINION ASTROPHYSICAL OBSERVATORY, VICTORIA, B.C. *** - - - - -Produced by Andrew Sly, MFR, David E. Brown, and the Online -Distributed Proofreading Team at https://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - - - - - - -</pre> - - - -<div class="figcenter"><img src="images/cover.jpg" alt="" /></div> -<hr class="chap" /> - - -<div class="figcenter"><img src="images/i_frontis.jpg" alt="" /></div> - -<p class="caption"><i>Frontispiece</i>—BUILDING AND DOME FROM SOUTH</p> - -<hr class="chap" /> - -<div class="figcenter"><img src="images/i_title.jpg" alt="" /></div> -<hr class="tb" /> - -<div class="titlepage"> - -<p><span class="bb">DEPARTMENT OF THE INTERIOR</span><br /> - -Hon. Charles Stewart<span class="gap"> Minister</span><br /> -W. W. Cory, C.M.G.<span class="gap2"> Deputy Minister</span></p> - - -<h1><small>The</small><br /> -Dominion Astrophysical<br /> -Observatory</h1> - -<p><span class="large">Victoria, B.C.</span></p> - -<div class="blockquot"> -<p class="drop-cap">A SKETCH of the development of astronomy -in Canada and of the founding of this observatory. -A description of the building and of the -mechanical and optical details of the telescope. An -account of the principal work of the institution.</p></div> - -<p>By<br /> -<span class="large">J. S. Plaskett, F.R.S.</span></p> - - -<p>Ottawa<br /> -F. A. ACLAND,<br /> -Printer to the King’s Most Excellent Majesty<br /> -1923</p> -</div> -<hr class="chap" /> - - -<p class="center"><b>STAFF OF THE OBSERVATORY:</b></p> - - -<table border="0" cellpadding="2" cellspacing="2" summary="table"> - - -<tr><td>Director</td><td class="tdr"> J. S. Plaskett, B.A., D.Sc., F.R.S.C., F.R.S.</td></tr> -<tr><td>Research Astronomer </td><td class="tdr"> W. E. Harper, M.A.</td></tr> -<tr><td>Astronomer </td><td class="tdr"> Reynold K. Young, Ph.D., F.R.S.C.</td></tr> -<tr><td>Astronomer </td><td class="tdr"> H. H. Plaskett, B.A.</td></tr> -<tr><td>Secretary </td><td class="tdr"> Miss H. R. Keay</td></tr> -<tr><td>Observing Assistant</td><td class="tdr"> T. T. Hutchison, Esq.</td></tr> -</table> - -<hr class="chap" /> - - -<div class="chapter"> -<span class="pagenum"><a name="Page_5" id="Page_5">[5]</a></span> - - - - - - -<p class="ph1">THE DOMINION ASTROPHYSICAL<br /> -OBSERVATORY</p> - -<p class="center"><span class="large"><b>VICTORIA, B.C.</b></span></p> - -<p class="center">By J. S. PLASKETT, Director.</p> - - - -<h2 class="nobreak">SECTION 1.—HISTORY AND CONSTRUCTION</h2></div> - - -<h3>Introduction</h3> - -<p>This description of the observatory, its equipment and -work has been written by the director in response to a need, -frequently expressed by the numerous visitors to the institution, -of a non-technical account of the principles of the -telescope and of the work of the institution. This account -will commence by a short historical sketch of the beginnings -of the undertaking followed by a description of the observatory -and telescope and concluded by a resume of its work.</p> - - -<h3>Historical Sketch</h3> - -<p>This observatory is a branch of the Department of the -Interior of the Federal Government, the department which -has charge of the administration of the western lands of the -Dominion. In the colonization of these lands, one of the -obvious first needs was a survey of the boundaries and subdivision -into townships and sections. This need led to the -organization of a surveys branch of the department and out -of the necessity of accurate astronomical observations to -delimit the boundaries and define the position of the base -lines for subdivision work arose the astronomical branch. -The first Chief Astronomer of Canada, the late Dr. W. F. -King, was a man of sterling integrity and remarkable ability -and to his genius must be ascribed in large degree the present -development of astronomy in Canada. As Chief Astronomer -and H. M. Commissioner of International Boundaries, he<span class="pagenum"><a name="Page_6" id="Page_6">[6]</a></span> -early realized the need of an observatory for an initial meridian, -for housing and standardizing the instruments, and for some -astronomical research. He was successful in having the fine -Dominion Observatory erected on the Experimental Farm, -Ottawa, in 1905 which housed the Astronomical Branch, -the staff of the International Boundary Surveys and later -the Geodetic Survey of Canada, of which he was the first -superintendent.</p> - -<p>The Dominion Observatory was equipped with a 15-inch -refractor provided with micrometer, photometer, solar and -stellar cameras, and spectrograph. The writer was entrusted -with the work with this telescope and the spectroscopic -work especially was energetically developed and helped, -with the other activities of the institution, to bring gratifying -recognition from the scientific world. The need of a larger -aperture for extending this part of the work was soon realized -by the writer and was brought to the attention of the Government. -After some delays, owing to various circumstances, -it was finally decided early in 1913 to provide a large reflector -for extending the work. Enquiries were at once made, -specifications prepared and estimates obtained from prospective -makers of the instrument. Contracts were finally -awarded in October 1913 to the John A. Brashear Co. of -Pittsburgh for the optical parts and to the Warner & Swasey -Co. of Cleveland for the mechanical parts of a 72-inch reflecting -telescope.</p> - - -<h3>Location</h3> - -<p>It was necessary to know the location of the instrument -before the design of the mounting could be completed as the -angle of the polar axis depends upon the latitude of the -site. When the new telescope was first proposed there was -no thought of locating elsewhere than at the seat of government -at Ottawa. However, upon further consideration it -was decided that the telescope should be located where, in -Canada, the best observing conditions prevailed. To determine -this location preliminary selection of five likely stations -was made by the aid of Sir Frederic Stupart, chief of the -Meteorological Service from the meteorological records.<span class="pagenum"><a name="Page_7" id="Page_7">[7]</a></span> -These stations, at Ottawa, at Medicine Hat, at Banff, at -Penticton, and at Victoria were occupied by Mr. W. E. -Harper, astronomer at Ottawa and the astronomical conditions -were observed by means of a 4.5-inch telescope. -Victoria was unmistakably superior in “seeing” or defining -power, in low diurnal and seasonal range of temperature and -about equal so far as quantity of clear sky is concerned. For -such a large telescope as a 72-inch there could be no question -of the marked astronomical advantages of such a location, -and it was therefore decided to locate the telescope at Victoria. -While the observatory should not be in the city itself it should -not be too far away, not only on account of accessibility and -facility in obtaining supplies, but also the advantageous -conditions of good seeing, low diurnal range of temperature -and small rainfall were confined to a relatively small area near -Victoria. An isolated monadnock called locally Little -Saanich Mountain but now named Observatory Hill, was -selected. This hill is about 7 miles north of Victoria and has -a main road and an interurban railway passing its base. It -has an elevation of 730 feet, sufficient area around the summit -for all necessary buildings and was by far the most suitable -site available.</p> - - -<h3>Construction</h3> - -<p>The Provincial Government had generously agreed to -give $10,000 for the purchase of a site and to build a road to -the summit. This undertaking was fully met and the road, -splendidly located and constructed and costing over $25,000, -was completed in the spring of 1915. Contracts for the -construction of the telescope pier and the circular steel walls -of the building were awarded to a local firm and this work -was completed in 1916. The revolving dome with accessories -for the operation of the telescope was made by the Warner -& Swasey Co., the builders of the telescope mounting, and -was completed and erected in 1916, thus making the building -ready for the telescope.</p> - -<p>The design of the mounting was very carefully gone into -by the Warner & Swasey Co. in collaboration with the writer -and was completed in the autumn of 1914. Construction<span class="pagenum"><a name="Page_8" id="Page_8">[8]</a></span> -was at once begun and the mounting was completed and -temporarily erected at Cleveland in May 1916. It was then -shipped to Victoria and permanently erected in its building -by November 1916.</p> - -<p>The order for the large disc for the 72-inch mirror and for -an auxiliary flat of 55 inches diameter for testing the 72-inch -was given to the St. Gobain Glass Works of Paris by the -Jno. A. Brashear Co. as soon as the contract was awarded. -The 72-inch disc was cast and annealed by June 1914 and -was fortunately shipped at once without waiting for the -55-inch disc. It left Antwerp only about a week before war -was declared and it was only by this small margin that Canada -now has a 72-inch telescope. Grinding and polishing were -at once begun but the lack of the large flat and other difficulties -delayed the completion and it was not until April 1918, about -a year and a half after the completion of the mounting, that -the figuring was finally completed and the telescope ready for -work. Nevertheless, for an undertaking of such magnitude -the work was completed in record time, four and a half years -after the awarding of the contracts.</p> - - - -<hr class="chap" /> -<div class="chapter"> - -<h2 class="nobreak">SECTION 2.—THE BUILDING AND DOME</h2></div> - - -<h3>The Observatory Building</h3> - -<p>The building for housing a large reflecting telescope requires -to be of special design for the best results. It should not -rise above the shade temperature during the day and should -rapidly assume and follow the external temperature at night. -Such materials as brick or stone are obviously not suitable and -all recent telescope buildings are entirely of metallic construction -in order to assume quickly the night temperature, -and of double-walled, ventilated type to prevent overheating -from the sun’s rays. The building for the 72-inch telescope -is entirely of steel construction, circular in form, 66 feet in -external diameter and with vertical walls 32 feet high. A -view from the south is given in the Frontispiece and from the -north in Fig. 1, showing the city of Victoria and the straits of -Juan de Fuca in the background. An external and internal<span class="pagenum"><a name="Page_9" id="Page_9">[9]</a></span> -covering of galvanized iron separated by about 16 inches allows -free circulation of air from a peripheral opening at the base -up through a similar double walled dome and out of louvres -at the top. The ground floor of Terrazo is laid directly on -the rock base and the observing floor 22 feet above this is -formed of steel girders and checkered steel plate. In the -centre of the ground floor rises the massive pier to support -the telescope, of reinforced concrete and symmetrical tapering -form. The pier is actually double, united below the observing -floor by a massive reinforced arch and extending above the -floor as two piers (see Fig. 2) one for each end of the polar -axis. Temporary partitions on the ground floor provide a -dark room, sleeping room, and temporary office quarters.</p> - - -<div class="figcenter"><img src="images/i_009.jpg" alt="" /></div> -<p class="caption">Fig. 1.—OBSERVATORY BUILDING FROM THE NORTH</p> - - -<p><span class="pagenum"><a name="Page_10" id="Page_10">[10]</a></span></p> -<h3>The Dome</h3> - -<p>This circular steel building is capped by a circular plate -supported by massive girders on which is placed a curved -railroad iron rail turned and adjusted perfectly level and -circular. The hemispherical dome turns on this rail on 24 -massive wheels mounted on roller bearings and is rotated by -an electric motor mechanism operated by reversing switches -on each side of the south pier. The framework of this dome, -which is 66 feet in external diameter and about 38 feet high, -the lower 5 feet being cylindrical, consists essentially of a -circular base to which the bearing wheels are attached and -two double, very deep and rigid main ribs, one of which can -be seen in Fig. 3, 16 feet apart in the clear and extending -parallel to each other entirely across the dome. These are -united 6 feet beyond the zenith by a cross girder and this -opening, which can be revolved to any azimuth and can be -closed by double motor operated shutters, enables the telescope -to observe at any part of the sky. Auxiliary circular ribs -reaching from the base ring up to the main ribs all around the -dome except at the shutter opening, form the support for the -double steel covering of 12 inches separation. This ventilating -space is united through suitable weather guards with the -space between the building walls and forms the protection -against overheating by the sun in the day time.</p> - -<p><span class="pagenum"><a name="Page_11" id="Page_11">[11]</a></span></p> - - -<h3>Dome Accessories</h3> - -<p>The shutter opening 16 feet wide and extending from the -base of the dome to 6 feet beyond the zenith is closed by a -double shutter also double walled and ventilated. Canvas -screens mounted on tubes and operated by motor can be run -up from the base of the shutter opening, this one being shown -in Fig. 3, and down from the top so as to limit the opening to -the width of the tube of the telescope. These screens are -necessary when the wind is blowing to prevent shaking of the -tube and consequent jumping of the star image. For enabling -the observer to reach conveniently the upper end of the -telescope tube in any position a counterweighted elevating -platform, moved up and down the shutter opening by motor -and drum with lifting cables is provided. This platform is 20 -feet long and 4 feet wide with a wing at each end, extending -inwards about 6 feet, on which the observer can stand and -can move it and himself by a hand wheel up to and partly -encircling the telescope tube. The platform and movable -wings, which are well shown in Fig. 3, can be brought to any -desired height by an operating switch at one side and can be -reached by an auxiliary stairway from a small stationary -platform attached to the base ring of the dome. This stationary -platform is reached from the observing floor by a permanent -stairway moving with the dome and extending to a foot -from the floor. Platform wings and stairways are made safe -for observers by guard and hand rails 30 inches high. This -moving platform, an essential accessory for direct photography -and other work at the principal focus of the telescope, -meets, in a more convenient and satisfactory manner than -any other previous device for the purpose, all the observing -requirements for work at the upper end of the tube.</p> - - -<h3>Mechanism for Silvering</h3> - -<p>In order to renew the silver coating on the upper surface -of the mirror, which is necessary about three times a year, -mechanism has to be provided for handling the mirror and -its cell, the lower section of the telescope tube, with ease and -safety. The mirror weighs over 2 tons and the cell 4 tons,<span class="pagenum"><a name="Page_12" id="Page_12">[12]</a></span> -so 6 tons have to be removed from and replaced on the telescope -tube. This is effected by means of the silvering car, which -can be seen at the left of Fig. 2, a massive framework of -structural steel rolling on four flanged wheels on flush tracks -in the observing floor. With the tube turned to a vertical -position, the car is rolled from its normal position at the -east side of the dome directly under the tube and a motor-operated -screw-jack surmounted by a triangular rocking -arm can be brought up against the bottom of the cell. On -removing the attaching bolts, cell and mirror can be lowered -and rolled on the car to the east out of the way. The removal -of 6 tons from one side throws the telescope out of balance and -so the outboard end of the declination axis is supported by a -counterweighted strut run up through the floor and the -upper end of the tube tied to rings at the top of the dome. -With a band of paraffined paper tied around the edge of the -mirror and a plug in the central hole, the silvering solution -can be poured on and evenly flowed over the surface by -rocking on a steel ball at the top of the jack-screw. When the -silvering is complete, cell and mirror are replaced in the reverse -order and the car rolled back out of the way. The operation -takes about a day and is performed with perfect safety and ease.</p> - -<p><span class="pagenum"><a name="Page_13" id="Page_13">[13]</a></span></p> - -<div class="figcenter"><img src="images/i_012.jpg" alt="" /></div> -<p class="caption">Fig. 2.—TELESCOPE IN AVERAGE OBSERVING POSITION</p> - - - -<hr class="chap" /> -<div class="chapter"> - -<h2 class="nobreak">SECTION 3.—MECHANICAL PARTS OF TELESCOPE</h2></div> - - -<h3>Introduction</h3> - -<p>It is useful, before describing the mechanical parts or -mounting of the telescope, to explain the difference between -the two kinds of telescope, refracting and reflecting, employed -in astronomical work. The refracting telescope is the most -familiar type as the ordinary spyglass or draw-tube telescope -and the field or opera glass are all refracting telescopes. The -refracting telescope is so called because the light from the -distant object is refracted through a lens at the outer end of -the tube and forms an image of the object at the inner end, -just as a camera forms an image on the ground glass or film, -and this image is viewed and magnified by the eyepiece or -ocular. The reflecting telescope on the other hand has the<span class="pagenum"><a name="Page_14" id="Page_14">[14]</a></span> -upper or outer end of the tube open and the light from the -distant object is reflected (hence the name) from a concave -mirror at the lower end of the tube, forming the image of -the object at the top, where it can be viewed and magnified -by the ocular as in the refractor.</p> - -<p>Each type of telescope has its astronomical advantages and -disadvantages. The refractor is better suited for visual -observations such as the measurement of double stars and the -study of planetary detail and is less affected by temperature -changes than the reflector. On the other hand the reflector, -on account of its perfect achromatism, is the instrument par -excellence for photographic observations, and, as more than -three-fourths of modern astronomical work is photographic, -it appears to be superseding the refractor. This advantage is -increased by the fact that the refractor has apparently reached -the useful limit in size and that it costs at least three times -as much as a reflector of the same aperture. Although each -type of telescope has its characteristic type of mounting for -astronomical purposes, the principles are the same for each -and can probably be most easily followed by describing the -essential parts of the mounting of the 72-inch telescope.</p> - - -<h3>The Telescope Tube</h3> - -<p>The tube performs the important function of carrying in -relatively invariable position and adjustment the optical -parts of the telescope. The tube of the 72-inch telescope is -31 feet long, 7 feet 4 inches outer diameter and weighs 15 -tons. Its form and construction are well shown in Figs. 2 -and 3. It consists of the main or central section A, Fig. 2 -the lower section B which carries the main mirror and the -skeleton section C which carries the secondary mirrors. -The central section is a cylindrical steel casting heavily -ribbed on the inside about 6 feet high and weighs 7 tons. -The lower section is securely bolted to it through the flanges -shown and with the mirror and its supporting mechanism -weighs about 6 tons. The upper skeleton section is built -up of structural steel, 3 inch I beams, firmly braced and -rivetted together in the manner shown in the figures. A<span class="pagenum"><a name="Page_15" id="Page_15">[15]</a></span> -special feature of this skeleton tube, making it more rigid -than any previous design, consists of the diagonal tension rods -in each rectangular compartment screwed up each to a tension -of about 2,000 pounds, so that the whole tube is under tension -in every position. This stiffness is essential for the proper -performance of the optical parts, as the principal and secondary -mirrors at bottom and top of tube respectively should -occupy the same relative positions in whatever direction the -tube is pointed.</p> - - -<h3>The Declination Axis</h3> - -<p>The telescope tube is firmly screwed at right angles to the -flanged end of a massive shaft 16 inches in diameter, called -the declination axis, extending through the cubical section -D of the polar axis NDS, Fig. 2, through the declination -sleeve E into the housing F. This declination axis is rotated, -carrying the tube with it, on ball bearings in D and F, this -rotation being effected by an electric motor with reduction -mechanism, gearing into a large spur gear attached to the -end of the declination axis, the whole being concealed within -the declination housing F. Hence the tube can be turned at -the rate of 45 degrees to the minute to any required position -up or down, north or south. The position in the sky, the -declination, corresponding to latitude on the earth, is read -on a large circle graduated into degrees within F and subdivided -into 5 minute intervals on the small auxiliary circle H.</p> - - -<h3>The Polar Axis</h3> - -<p>As positions north or south are given by turning the tube -on the declination axis, so positions east or west are given by -rotation on the polar axis, so called because it points to the pole -of the heavens and is exactly parallel to the axis of the earth. -The Polar axis NDS Fig. 2, which is 21 feet long and weighs -95 tons, is built up of three steel castings, a central cubical -section D and two conical end sections, all securely bolted -together and turning in ball bearings on its ends. The -upper, north, bearing is carried in an adjustable pillow block, -by which the final parallelism with the earth’s axis is obtained,<span class="pagenum"><a name="Page_16" id="Page_16">[16]</a></span> -bolted on the curved cement pier shown at the left or north in -Figs. 2 and 3. The lower, south, bearing is carried in a -massive cast iron pedestal bolted to the south cement pier. -The polar axis is rotated on these bearings, also at the rate of -45 degrees per minute, carrying the declination axis and tube -with it to any position east or west in the sky by an electric -motor and reduction gearing concealed within the south -pedestal. The position east or west in the sky, the right -ascension as it is called corresponding to longitude on the -earth, is read by means of a graduated circle shown above -G, Fig. 2, which is divided into 24 hours and each hour into -single minutes. While longitudes on the earth are occasionally -expressed as so many hours and minutes east or west of -Greenwich, right ascensions in the sky are almost invariably -given in hours and minutes rather than degrees.</p> - -<p><span class="pagenum"><a name="Page_17" id="Page_17">[17]</a></span></p> - -<div class="figcenter"><img src="images/i_016.jpg" alt="" /></div> -<p class="caption">Fig. 3.—TELESCOPE FROM THE WEST</p> - - -<h3>The Driving Clock</h3> - -<p>It is evident, by rotation of the telescope on the declination -and polar axes by means of the quick-motion motors, that the -tube can be pointed in any direction in the sky, towards any -star. But owing to the rotation of the earth on its axis from -west to east, which is the cause of the apparent motion of -sun, moon and stars from east to west, the telescope will be -quickly carried eastward of the star which will only remain -for an instant in the field.</p> - -<p>The mechanism by which the rotation of the earth is -compensated for is called the driving clock and is contained in -the case L, Fig. 2, at the north side of the south pier. In the -lower half of the case a governor similar to the governor of a -steam engine is driven once per second by a train of gears in -the upper section actuated by a weight of 300 pounds below -the floor. If the speed of the governor tends to increase the -balls raise by centrifugal force and bring increased friction to -bear thus reducing the speed to normal while if the speed -tends to decrease, the balls drop and reduced friction quickly -allows it to accelerate to normal speed. A shaft with a coarse -screw thread on it, called technically a “worm” and situated -at the top of the case, is driven by intermediate gearing from<span class="pagenum"><a name="Page_18" id="Page_18">[18]</a></span> -the governor at the rate of one revolution every two minutes. -The thread on this shaft engages into teeth cut in the worm -wheel G, Fig. 2, which is 9 feet in diameter. As there are -720 teeth very accurately spaced in this worm wheel, it is -driven around by the worm in 2 720 = 1,440 minutes, 24 -hours, the same rate as the earth. This worm wheel, normally -loose on the polar axis on which it turns on ball bearings, -allowing the axis to be moved freely to any position, can be -rigidly clamped to it by pressing a button. When this is -done, it will evidently turn the polar axis and hence the tube -at the same rate as the earth but in the opposite direction, -on an axis parallel to the axis of the earth, thus exactly compensating -for the rotation of the earth. Hence any star at which -the telescope is pointed will automatically remain central in -the field. Owing to the great magnification all this mechanism -requires the highest grade of workmanship, else there will be -wandering of the image, a most annoying and troublesome -defect. Few telescopes are entirely free from periodic error -and that the 72-inch drives so regularly and smoothly is a -great advantage and evidence of the perfection of workmanship -throughout.</p> - - -<h3>Electric Motions</h3> - -<p>It has already been described how the telescope can be -moved by motors north or south and east or west at the rate of -45 degrees per minute. These motors are operated from small -switchboards on each side of the south pier, the one at the -west being seen in Figs. 2 and 3. The left-hand reversing -switch moves the telescope east or west, the centre switch -north or south and the right-hand switch revolves the dome -east or west. In addition to these quick motions of the -telescope for rapidly bringing it to the approximate position, -much finer and slower motions are required for bringing the -image exactly central and for guiding. These slow motions -are also operated by electric motors actuated by two small -aluminium switchboards attached by flexible cables to the -top and bottom of the tube. These switchboards can be -carried in the hands of the observer or rested on the observing<span class="pagenum"><a name="Page_19" id="Page_19">[19]</a></span> -ladder. Pressure on suitable buttons moves the telescope -north or south, east or west at either one of two different -speeds, a speed of one revolution in 36 hours for centering the -image and a speed of one revolution in 30 days for guiding, -correcting for slight irregularities due to air disturbance or -other causes. Although these speeds may seem excessively -slow, the motion of the image even with the monthly rate is -at once evident on pressing the button and faster speeds -would make accurate guiding difficult. In addition to the -two quick and two slow motion motors there are two clamping -motors and one for automatically rewinding the clock weight, -seven in all. These with the three motors operating the dome -are all continuous current motors which can be started and -reversed more readily and have greater initial torque than -alternating motors. Each motor is supplied with an automatic -control, so that all that is necessary is to throw the -switch or press the button to start or reverse. Current is -supplied by a motor generator set on the ground floor.</p> - - -<h3>Method of Operation</h3> - -<p>A description of the method of setting upon the required -star, when, for example, photographing the spectra of the -stars, will help to make the operation of the telescope more -clearly understood. It is easily possible to pull the telescope -around by hand to the required star identified by eye among -the constellations. Although the moving parts of the telescope -weigh nearly 45 tons, so perfect are the ball bearings in which -it turns that a weight of 3 pounds at the upper end of the tube -is sufficient to set it in motion. However the settings can be -much more quickly and certainly made by turning the telescope -to the right ascension and declination of the star by the -electrical motions. A programme of the stars to be observed -with their right ascensions and declinations is prepared beforehand. -The observing assistant stands beside the small -switchboard on the south pier and rapidly moves the telescope -east or west and north or south until the indexes on the -graduated circles point to the tabulated positions, while the -dome can be turned to the required position at the same time<span class="pagenum"><a name="Page_20" id="Page_20">[20]</a></span> -by means of the third operating switch. By pressing two -buttons the telescope is then firmly clamped and the driving -clock starts the telescope automatically following the star. -In the meantime the observer has inserted the plate holder in -the spectrograph and drawn the slide and by means of the -aluminium switchboard brings the star, which is generally -near the centre, exactly to the centre of the finder, when it -will be visible on the slit of the spectrograph through a guiding -eyepiece and can quickly be brought central and the exposure -commenced. The time required from the end of one exposure -to the beginning of the next, unless the stars are far apart in -the sky, does not generally exceed two minutes, a shorter -time than usually required for even quite small telescopes. -This rapid operation is due to special care in design and -construction and markedly increases the efficiency and -capacity of the instrument.</p> - - -<h3>Special Features of the Mounting</h3> - -<p>The mounting of the 72-inch telescope has several new -features not hitherto used and sets a new standard for convenience -and accuracy of operation. The observatory is -much indebted to the Warner & Swasey Co., who have made -most of the large mountings in America, for the spirit in which -they undertook and carried through this work. Their sole -object was to produce the best possible mounting regardless -of cost and no suggestion of the writer looking to improvement -was refused. To Mr. Swasey, the president, are due many of -the original features of the mounting and the beauty and -harmony of the design, while Mr. Burrell, the works manager, -is responsible for the simplification of the mechanism and the -beautiful co-ordination of the details. No greater testimony -to the perfection of design and construction can be given -than to say that after five years use there is no feature the -director would wish changed, and no single defect of construction -has been revealed.</p> - -<p>It may be of interest to note the principal improvements in -this mounting.</p> - -<p>1. All parts of the sky can be readily reached. This is not -possible with all types of reflecting telescopes.</p> - - - -<p><span class="pagenum"><a name="Page_21" id="Page_21">[21]</a></span>2. The elimination of cylindrical bearings with cumbrous -friction-relieving devices, formerly considered necessary for -maintaining collimation and adjustment on declination and -polar axes, and the use of ball bearings for both friction-relieving -and collimating purposes has resulted in remarkable -ease of movement of the telescope.</p> - -<p>3. Freedom from periodic or other errors in driving and -smoothness and freedom from “backlash” in slow motions.</p> - -<p>4. Ease, speed and accuracy with which settings can be -made due to careful design and original features in setting -motors and setting circles.</p> - -<p>5. Great stiffness of tube and improvements in method of -attaching and changing secondary mirrors.</p> - -<p>6. Beauty and harmony of design and appearance.</p> - - - -<hr class="chap" /> -<div class="chapter"> - -<h2 class="nobreak">SECTION 4.—OPTICAL PARTS AND SPECTROGRAPHS</h2></div> - - -<h3>The Principal Mirror</h3> - -<p>The great mirror is composed of hard plate glass cast in -one piece and after annealing, ground and polished to the -correct shape. As received from the St. Gobain Co., the disc -was 735 inches diameter, over 13 inches thick with a central -hole about 6 inches diameter and weighed nearly 5,000 pounds. -It was first of all ground truly circular to a diameter of 73 -inches and flat on both sides to a thickness of slightly over -12 inches, while the central hole was enlarged to 10 inches. -When the back was polished approximately flat, the disc -was seen to be a beautiful specimen of the glass makers art, -homogeneous and almost entirely free from bubbles or other -defects.</p> - - -<div class="figcenter"><img src="images/i_022.jpg" alt="" /></div> -<p class="caption">Fig. 4.—PHOTOGRAPH OF RING NEBULA IN LYRA<br /> - -(<i>Enlarged 8 diameters</i>)</p> - -<p>It was now ready for the second stage of the operation the -grinding of the correct shape for the upper reflecting surface. -In order to bring the light of a star to an accurate focus this -surface must be a paraboloid of revolution, the same kind of -curve given to the reflectors of search lights or automobile -headlights. The curve for this reflector of 30 feet focus is -very nearly a section of a sphere of 60 feet radius, within<span class="pagenum"><a name="Page_22" id="Page_22">[22]</a></span> -one-thousandth of an inch, and consequently would nearly -fit a huge globe 120 feet in diameter. The upper surface of -the disc was fine ground and polished to this spherical surface -and was then ready for the final stage, the “figuring” a continuation -of the polishing process until the centre is deepened -about a thousandth of an inch and the surface becomes -accurately paraboloidal. This “figuring,” an exceedingly -delicate and difficult process especially over such a large -surface as the 72-inch, with the added difficulty of a central -hole, occupied about two years and was not completed until -nearly a year and a half after the mounting was ready. When -it is remembered, however, that the surface nowhere deviates -from the true theoretical form more than one four-hundred-thousandth -of an inch and that if one part is accidentally -polished too deep, the whole surface has again to be brought -down to this level, the exceeding delicacy of the operation is -evident and the time taken not excessive.</p> - -<p><span class="pagenum"><a name="Page_23" id="Page_23">[23]</a></span>Accurate quantitative tests showed that the final figure is -of the highest order of accuracy and this is further clearly -shown by the practical test of direct photographs at the -principal focus. Figure 4, a six fold enlargement of a photograph -at the principal focus, of the Ring Nebula in Lyra -shows how sharp and small are the star images. Actual -measurement on the original negative gives a minimum -diameter of two one-thousandths of an inch equivalent to -only a second of arc at the focus. As the images are enlarged -considerably by unsteadiness of the air and errors in guiding -the star light reflected from the whole surface of the mirror -is collected into a little disc less than a thousandth of an inch -in diameter indicating the extraordinary accuracy of the -reflecting surface. Mr. J. B. McDowell, head of the firm -since Dr. Brashear’s death, and Mr. Fred Hegemann, his -chief optician, are to be highly congratulated on the perfection -of figure obtained under specially difficult circumstances. -Further the fine rendering of the detail in the -ring and the strength of the two bands in the interior indicate -not only perfect figure but exceptionally high polish.</p> - -<p><span class="pagenum"><a name="Page_24" id="Page_24">[24]</a></span></p> - - -<h3>Mounting of Mirror</h3> - -<p>This mirror, to maintain its accuracy, not only requires -careful mounting in its cell but also protection against temperature -changes. Even though 12 inches thick it would bend -under its own weight of 4,300 lbs. sufficiently to affect the -figure and consequently it is supported in the cell by a specially -counterweighted lever system so that it is equably supported -at twelve points and there is no tendency to bend. A similar -lever support system around the edge prevents distortion -due to constraint when it is tipped from the horizontal position -at different positions of the tube. Temperature changes can -produce much greater distortion than flexure but Victoria -has the advantage of very low diurnal range and the temperature -change around the mirror is made very small by a lagging -of cotton felt about 2 inches thick all round the sides of the -closed section of the tube, laced on with a duck cover (compare -Fig. 3 with Fig. 2) and an equal thickness below and around -the edge of the mirror. By this lagging the temperature rise -in the day-time is only about half a degree while the dome -temperature increases five degrees, hence the figure of the -mirror remains good whatever the temperature changes -outside.</p> - - -<h3>The Principal Focus</h3> - -<p>As already indicated, the principal mirror when used alone -forms an image of the star 30 feet above, at the centre of -the upper end of the tube, and an eyepiece could be placed -there for visual work or a photographic plate for direct photographs -of nebulae, etc. However, it is generally more convenient -to use a flat mirror at 45 forming the image at the -side of the tube for photographs and so the telescope is only -used in this form with a small spectrograph for the ultra-violet -region of star spectra. The course of the parallel -beam of light from the star to its image on the slit of the -spectrograph is graphically shown in Fig. 5 A and also its -passage through the slit prisms and lenses of the spectrograph. -The position of the star image on the slit of the -spectrograph can be observed by a guiding telescope extending<span class="pagenum"><a name="Page_25" id="Page_25">[25]</a></span> -to the edge of the tube and can be kept central by the portable -aluminium switchboard already described. The elevating -platform is of course used in work in this position.</p> - - -<h3>The Newtonian Arrangement</h3> - -<p>For direct photography or visual observations at the focus -of the 72-inch mirror, the reflected cone of star light from the -mirror B, Fig. 5, is intercepted by a plane mirror also silvered -on the front surface, 195 inches diameter and 325 inches -thick placed at 45. This form of reflecting telescope was -first used by Newton, hence the name. The focus is then -formed, as shown, at the side of the tube, and if a plate is -placed there and accurately guided by small eyepieces with -cross wires, photographs of any desired small region in the -sky can be obtained, Fig. 4 being made in this position, or -visual observations may be made. The oculars can easily be -reached from the observing platform for any position of the -telescope.</p> - - -<h3>The Cassegrain Arrangement</h3> - -<p>The most generally useful arrangement of the 72-inch -telescope is, however, the Cassegrain form, so called from -the French astronomer who first used it. About 7 feet below -the focus, the conical reflected pencil from the 72-inch mirror -is intercepted by a convex mirror of the same size as the -Newtonian and of about 10 feet focal length as seen in C, -Fig. 5, and also shown in Fig. 2 and 3. This mirror turns the -light downward and, after passing through the central hole, -forms the image of the star about two feet below the mirror -surface on the slit of the spectrograph or on a visual attachment -as shown. The significant property of this combination -is that the focal length is increased from 30 to 108 feet without -changing the tube length in a somewhat similar manner to -the action of a telephoto lens. It has the same size of image -and magnifying power as a refractor with a tube 108 feet long -and has the decided advantage of a much shorter tube and -smaller dome. Observations with this arrangement are -made at the lower end of the tube from the observing floor and<span class="pagenum"><a name="Page_26" id="Page_26">[26]</a></span> -with much greater ease and convenience than at the upper -end. Changes from the Cassegrain to the Newtonian or -Principal Focus arrangements are readily effected by a device -due to the genius of Mr. Swasey whereby only the mirrors -and attaching tubes require to be handled, instead of the -whole upper end of the tube as in previous reflectors.</p> - - -<div class="figcenter"><img src="images/i_026.jpg" alt="" /></div> -<p class="caption">Fig. 5.—COURSE OF LIGHT IN TELESCOPE FROM STAR TO FOCUS</p> - -<p><span class="pagenum"><a name="Page_27" id="Page_27">[27]</a></span></p> -<h3>Accessory Optical Parts</h3> - -<p>A full set of eyepieces giving magnifying powers from 120 -to 5,000 diameters and a complete double-slide plate holder -with guiding eyepieces for direct photography at the Newtonian -focus are provided. In addition there is a visual -attachment shown in diagram C, Fig. 5, which enables the -telescope to be used visually at the Cassegrain focus without -removing the spectrograph. There are three finders attached -to the telescope tube for picking up and centering the stars. -Two of 4 inch aperture and 5 feet focus, of power about 50, -one north, one south on the tube, and a long focus tubeless -finder with a lens of 7 inch aperture and 30 feet focus at the -top of the telescope tube and an ocular of power 200 at the -bottom.</p> - - -<h3>The Spectrographs</h3> - -<p>Most of the astronomical work with the 72-inch telescope -is spectroscopic, photographing the spectra of the stars, and -so a description of the principles and operation of spectrographs -is desirable. Stellar spectrographs have evolved into -certain definite forms and the two spectrographs for the -72-inch telescope are examples of the most recent types. In -essence a spectrograph consists of a narrow slit, one or two-thousandths -of an inch wide, on which the star light is focussed. -That passing through the slit falls on the collimator lens which -makes it parallel and then on a prism or prisms, triangular -shaped pieces of glass which change the direction of the -light and decompose it, breaking it up into its constituent -rainbow colours. The spectrum, as it is called, is focussed -by a camera lens on a photographic plate or can be viewed -by a small telescope if desired. The course of the star light<span class="pagenum"><a name="Page_28" id="Page_28">[28]</a></span> -from the slit through collimator, prism and camera lens to -the plate is shown in C, Fig. 5, while a view of the Cassegrain -spectrograph showing the interior mechanism and accessories -is given in Fig. 6. The part of the spectrum photographed -is usually only the blue and violet region to which the ordinary -plate is most sensitive, and obviously no colours appear on -the negative but only a narrow dark strip which is crossed by -light or dark lines. It is from the number and position of -these lines that we obtain such a remarkable amount of -information about the physical and chemical constitution, -the temperature, motion and distance of the stars. The -length of the star spectrum photographed with one prism is -about one and a third inches, twice and three times that with -two and three prisms. Its width is about one-hundredth of -an inch and in order to make it this wide the star image has -to be moved back and forward along the slit. The length of -spectrum with the ultra-violet spectrograph, which only -differs from the other in the prisms and lenses allowing the -spectrum below the violet to pass, is about one inch. A -photograph of the spectrum of iron or brass is made beside -the star spectrum to serve as a standard to determine the -positions of the star lines.</p> - -<p><span class="pagenum"><a name="Page_29" id="Page_29">[29]</a></span></p> - -<div class="figcenter"><img src="images/i_028.jpg" alt="" /></div> -<p class="caption">Fig. 6.—STELLAR SPECTROGRAPH ARRANGED FOR USE WITH ONE PRISM<br /> - -(TEMPERATURE CASE REMOVED)</p> - - -<h3>Method of Use</h3> - -<p>Every terrestrial element gives groups of lines in certain -positions in the spectrum and if we find similar groups in the -star spectrum we are sure this element is present in the star. -Further if we find these lines are displaced to red or violet of -their normal position we know that the star is receding from -or approaching to us. With the one-prism spectrograph a -speed of one mile per second means a displacement of the -lines of one thirty-thousandth of an inch. Thus if the lines -are shifted to the violet by a thousandth of an inch, the star -is approaching the earth with a speed of 30 miles a second. -These displacements are accurately measured by a microscope -and the measurement of the radial velocities of the stars is -one of the main researches of this observatory. Obviously -with such small displacements to be measured the greatest<span class="pagenum"><a name="Page_30" id="Page_30">[30]</a></span> -care must be taken to avoid all sources of error. The spectrograph -must be exceptionally rigid to avoid differential bending -as it moves with the telescope. As change of temperature can -produce spurious shifts of the lines, the temperature must be -kept as constant as possible, this being effected here by a -very accurate electrical thermostatic device called the Calendar -Recorder which maintains the temperature constant -to one-hundredth of a degree. The optical parts must be of -the highest quality to give perfect definition to the spectrum -lines and many other precautions must be taken if accurate -work is desired. The spectrographs of the 72-inch telescope -have unequalled defining power and are the last word in -convenience of manipulation and accuracy of work.</p> - -<p>Owing to the faintness of the star light and to its being -spread out into a spectrum a considerable time is required to -photograph the spectrum of a star, about 20 minutes for the -sixth magnitude, the limit of visibility to the unaided eye, -when photographed with one prism, while three prisms will -take nearly five times as long. Hence the necessity and use -of large telescopes is not to get high magnifying power but to -collect sufficient light from the fainter stars to enable their -spectra to be photographed or other observations made.</p> - - - -<hr class="chap" /> -<div class="chapter"> - -<h2 class="nobreak">SECTION 5.—THE WORK OF THE TELESCOPE</h2></div> - - -<h3>Prevalent Misconceptions</h3> - -<p>The general idea of an astronomer’s work, as gathered -from the questions and remarks of visitors, is that he sits at -the eyepiece of the telescope sweeping the heavens in a search -for new planets, comets or stars. The absolute futility of -such a use of the telescope is evident when it is realized that -the main field of the 72-inch covers only about one hundred-millionth -of the sky and if only five seconds was required to -examine each field it would take more than a lifetime to go -over the whole sky once. A second misconception is the idea -that large telescopes are used for visual observations of the -planets with special reference to their habitability. No -work is being attempted at this or other large observatories<span class="pagenum"><a name="Page_31" id="Page_31">[31]</a></span> -on planetary detail for which about an 18-inch refractor gives -the best results and such a large telescope as the 72-inch is -quite unsuited. All scientific observations with the 72-inch -are made photographically and it is only arranged for visual -use on Saturday evenings when for two hours visitors are -allowed to observe the heavenly bodies. A third misconception -is that the astronomer only works at night. However -true this idea may have been in the days of visual observations -when the measurements were made at the eyepiece, there is -certainly now, when photography is so generally applied, more -day than night work in astronomy. Besides the advantages -of permanency, accuracy of measurement and power of recording -objects beyond the range of the keenest eyesight, the -photographic method has the further great advantage that -an hour’s exposure may give sufficient material for several -days’ measurement and discussion.</p> - - -<h3>Spectroscopic Work</h3> - -<p>As already indicated most of the work with the 72-inch -telescope is spectroscopic, but as also indicated modern -spectroscopic investigations cover so wide a range of research -that the actual work of the observatory is very varied. By -aid of suitable spectrographs attached to a large telescope -we can measure the speed of the stars towards or from us, -their radial velocity as it is termed. We can discover double -stars too close ever to be seen double in any telescope and we -can determine the manner in which they revolve around one -another and their distance apart and mass. From the spectra -of the stars we can determine their absolute brightness as -compared with the sun and their parallax or distance. The -chemical elements present in the outer atmospheres of the -stars can be determined and the pressure in these atmospheres. -The measurement of temperatures and other physical conditions -in the stars by means of the spectroscope is now an -accomplished fact and one of the most recent developments of -the spectroscopic work here has been to provide evidence of -the truth of a theory of atomic structure and to show that the -atomic constants in the enormous furnaces of the stars are<span class="pagenum"><a name="Page_32" id="Page_32">[32]</a></span> -the same as on the earth. Such a catalogue of information, -obtained from an investigation of the mere quality of the -light from stars so faint as to be quite invisible to the unaided -eye and so distant that it may take thousands of years to -travel to us, is sufficiently comprehensive to be treated in -more detail.</p> - - -<h3>Radial Velocities</h3> - -<p>When the 72-inch telescope was in course of design and -construction, one of the greatest needs in astronomical work -was increased data in regard to the radial velocities of the -stars. Although the telescope was so designed as to be -suitable for all kinds of observational work, special attention -was devoted to the spectroscopic end. After consultation -with the most prominent astronomers an observing programme -of about 800 stars whose “proper” or cross motions across -the sky were accurately known but whose radial velocities -had not been determined, was prepared and spectroscopic -observations of the stars on this programme were commenced -as soon as the telescope was completed in May 1918. After -slightly over three years’ work, observation and measurement -were completed and Vol. II, No. 1 of the observatory -publications, “The Radial Velocities of 594 Stars,” was -published early in 1922. As hitherto the radial velocities of -only about 2,000 stars had been obtained, this work was a -considerable addition to existing data about the motions of -the stars and will be of great use in extending our knowledge -of the structure and motions of the universe. A second -programme of 1,500 stars has been prepared but owing to -other intervening observational work, not much has yet been -done on this new programme.</p> - -<p>One of the auxiliary programmes undertaken and nearly -completed since the first programme is the determination of -the radial velocities of a very interesting but limited class of -stars, the highest temperature stars known, the O-type stars. -The radial velocities and other interesting data about 50 of -these stars have been completed.</p> - -<p><span class="pagenum"><a name="Page_33" id="Page_33">[33]</a></span></p> - - -<h3>Spectroscopic Double Stars</h3> - -<p>In the measurement of the radial velocity of the 800 stars -on the first programme it was found that in about 180 stars -successive plates did not give constant velocities, the stars at -one time approaching at another receding from us. This -phenomenon is practically certain proof that we are measuring -the velocity of a star revolving around an invisible companion -and such stars are generally called spectroscopic binaries to -distinguish them from visual binaries which can be seen -double in the telescope. Over 200 spectroscopic binaries -have been discovered at this observatory as compared with -about 700 discovered elsewhere, again a considerable addition. -In about 20 of these binaries, observations were continued -until the period of revolution, the form of the orbit, the -separation of the two stars and in some cases, their masses -were determined. In a particular class of spectroscopic -binaries, the eclipsing variables, which allow from the combination -of spectroscopic and photometric measurements -the absolute dimensions to be obtained, we were able to -determine the separation of the two stars, their diameters, -densities, masses and brightnesses and the probable distances. -Such complete information has been obtained here about -seven systems, while only seven other systems have been -determined elsewhere.</p> - - -<h3>Absolute Magnitude and Distance</h3> - -<p>A new application of spectroscopic methods is to the -determination of the total brightness of the stars as compared -with the sun and their distance or “spectroscopic parallax” -as it is called. This depends not on the positions but on the -relative intensity or strength of the lines in the spectra of -the stars and has only been developed in the last three or four -years. The absolute magnitude and spectroscopic parallax -of about 800 stars is now nearly completed and will soon be -published while as a side line the radial velocities of 125 more -stars have been determined.</p> - -<p><span class="pagenum"><a name="Page_34" id="Page_34">[34]</a></span></p> - - -<h3>Physical Conditions in the Stars</h3> - -<p>The spectrographs have also been used by one member of -the staff in the determination of the physical and chemical -conditions in stellar atmospheres, a new and difficult problem -but one which promises not only very valuable additions to -our knowledge of the constitution of the stars but may also -lead to economic applications of the greatest importance. -A new method depending upon the use of a wedge of dark -glass has been applied to determining the distribution of -energy in the different parts of the spectrum of the stars and -to measuring their temperatures, while an application of the -same methods to individual lines may lead to a great increase -in our knowledge of conditions in the stars. A special investigation -of three of the high temperature O-type stars referred -to above has proved the existence in the spectra of these -stars of lines predicted as present from purely theoretical -conditions but never previously identified and has thus -remarkably verified a theory of the structure of the atom. -The measurement of the wave lengths of these hitherto -unknown lines has led to an important independent determination -of the fundamental constants of atomic structure and -the dimensions of the atom and has shown that these constants -and dimensions are the same in the tremendous furnaces of -the stars as in our terrestrial laboratories, a verification of -the homogeneity of matter and the uniformity of physical -laws throughout the universe. Further interesting results -from this investigation are the application of a new theory -of ionization with the probable relative abundance of the -elements to an independent determination of the temperature -of these stars.</p> - - -<h3>Other Investigations</h3> - -<p>Direct photographs have been made of some nebulae and -clusters but this work is not being definitely followed at -present. Investigations into the phenomena accompanying -some short period binaries have been made and into the -behaviour of the two strong calcium lines H and K in the -spectra of the high temperature stars from which interesting -and valuable results are expected. Since the observatory<span class="pagenum"><a name="Page_35" id="Page_35">[35]</a></span> -commenced work two bright novae or new stars have appeared, -which have been fully observed spectroscopically here and -the results discussed. The plates of the nova in Aquila have -been loaned to the observatory at the University of Cambridge, -England, for fuller discussion and analysis.</p> - - -<h3>Value of Astronomical Work</h3> - -<p>This brief sketch of the work of the observatory naturally -leads to the question frequently asked of astronomers:—What -use is the work done at observatories and what practical -value can a knowledge of the stars have in everyday life? -While astronomy has obvious practical applications to navigation -and surveying yet nine-tenths of modern astronomical -research is devoted to the more or less abstract question of the -constitution and motion of the stars and the structure of the -universe. Indeed most physical and chemical as well as -astronomical research is undertaken for the purpose of increasing -our knowledge and of investigating the secrets and laws -of nature and has generally no direct practical economic -application. But it is now generally recognized by the -layman as well as the scientist that without abstract there -can be no applied science and that all the great economic -and industrial applications of science have had to be preceded -by the abstract and apparently non-practical investigations -of pure science. The Great War perhaps made more evident -than ever before the absolute dependence of applied science -upon the unselfish and abstract work of pure science.</p> - - -<h3>Economic Value</h3> - -<p>In view of past experience in science it would hence be -a rash prediction to assert that the investigation of the conditions -in distant stars can have no practical application -upon earth. It may be of interest to point out one possible -application of astrophysical research.</p> - -<p>It is generally agreed that one of the most important -economic problems of the not far distant future will be the -provision of sources of energy to replace our rapidly depleting -supplies of coal and oil. It appears now that the most probable<span class="pagenum"><a name="Page_36" id="Page_36">[36]</a></span> -solution of this problem will consist in the development of -some method for utilizing the inexhaustible stores of energy -contained in the atoms of matter. Modern research on -conditions in the stars has made it practically certain that the -enormous supply of energy, which has been radiated into space -for aeons of time from these bodies, can only be maintained -undiminished by the energy released by the transformation of -atoms in the interior of the stars, where conditions of temperature -and pressure prevail at present unattainable in terrestrial -laboratories. The most hopeful line of attack upon this -tremendously important economic problem hence seems to lie -in the systematic astrophysical investigation of conditions in -the stars supplemented by physical and chemical researches -on the structure of the atom.</p> - - -<h3>Ethical Value</h3> - -<p>While astronomers and scientific men generally fully -realize the value of the practical applications of science, their -main purpose is the search for truth and the extension of our -knowledge of nature. While it is possible that investigation -of the stars may have immense economic value, it is certain -that it has tremendous ethical value giving us a clearer knowledge -of the laws of nature and of our relations to the wonders -of creation. Astronomy is the oldest and in many respects -the most important of the sciences and its study, through the -ages has been one of the most elevating influences on human -character. Poincar has well said that if the earth had been -so continuously covered with clouds that the heavenly bodies -could not be seen, mankind would still be in a primitive state -and under the domain of superstition. The main superiority -of modern over ancient civilization does not consist in the -greater abundance of the necessities and luxuries of life, -although this is undoubtedly due primarily to scientific -research, but to the elevating influences of the truer conceptions -of nature made possible by the abstract study of astronomy -and other sciences.</p> - -<p>It has been truly said that the degree of civilization of a -country may be judged by the support it gives to the study<span class="pagenum"><a name="Page_37" id="Page_37">[37]</a></span> -of astronomy. By the establishment and maintenance of the -Dominion Observatory at Ottawa and of the Dominion -Astrophysical Observatory at Victoria with the second largest -telescope in the world, Canada has a just claim on this criterion -to the favourable estimation of the scientific world.</p> - -<p> </p> - -<p>VICTORIA, B.C.,<br /> - May, 1923.</p> - -<hr class="chap" /> - -<div class="transnote"> - -<p class="ph2">TRANSCRIBER’S NOTE:</p> - - -<p>Obvious typographical errors have been corrected.</p> -</div> - - - - - - - - -<pre> - - - - - -End of the Project Gutenberg EBook of The Dominion Astrophysical Observatory, by -John Stanley Plaskett - -*** END OF THIS PROJECT GUTENBERG EBOOK DOMINION ASTROPHYSICAL OBSERVATORY, VICTORIA, B.C. *** - -***** This file should be named 62557-h.htm or 62557-h.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/6/2/5/5/62557/ - -Produced by Andrew Sly, MFR, David E. 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