THE OPENING PART of the account which follows will be found on page 347, the purpose in dividing it between two parts of the magazine being to present there only the general details of the Goethe Link Observatory, such as are likely to interest all the magazine's readers, reserving the more technical parts for special followers of the telescope makers' department. The author of the present account, Victor E. Maier (1306 Parker Ave., Indianapolis, Ind.), is known to amateur telescope makers everywhere, for he has long been active in the hobby. The 36" Goethe Link reflector is believed to be the largest telescope built by amateurs since this magazine have an ancient but nearly extinct hobby its renaissance in 1926 by publishing an instruction book. The old lines between amateur and professional telescope makers have largely dissolved. Nearly all the great professionals were men who started small and, generally working by themselves, simply developed the art through character, perseverence, tenacity. Few had much help. Many amateurs among the thousands who had followed the hobby have now learned to do large work equally well and through the same approach. The professional, who works at it all the time. can beat the advanced amateur in speed. Some amateurs, because they do not have to make their living through the work, can afford to take more time, and thus have done better work than some professionals. The description by V. E. Maier continues:

"The observatory stands on a high promontory 25 miles southwest of Indianapolis, near the small village of Brooklyn. From it the Indiana terrain is visible for 40 miles. The building is framed of oak posts and beams cut from the forests not far distant: 13 tons of steel beams were also used in construction, arc welding being employed wherever possible.

"The designers of the observatory and its equipment have sought to include the best features of all the observatories, together with as many innovations as could be used profitably. The design of the building itself was inspired by Russell W. Porter, who generously sent one of his famous thumbnail sketches to Indianapolis. Details were drawn up by A. F. Pittman, an Indianapolis 'TN.' The larger hemispherical dome, 34 feet in diameter, is framed of wood fastened to a 12" I-beam dome ring. It rolls on tapered roller bearings and is driven with an endless cable fitted with a unique shock absorbing device. The 34-ton dome is rotated adequately by a 1/2 h.p. electric motor. The broad slot opening, nearly three times as wide as the mirror, permits easy manipulation between the dome and the telescope. The zenith is accessible in any azimuth of the opening. The shutters weigh one ton each, and are activated by push buttons and a 1/4 h.p. motor. Dome and shutters are covered with interlocking sheets of steel terneplate and aluminum paint.

"The 36" Goethe Link reflector has several features that are thought to be new. The concrete pier was poured before the building was erected. It is anchored to bed rock to prevent vibration or future misalinement. The steel bearing boxes for the polar axis are bedded directly in the concrete, making the pier a direct part of the telescope mounting. The pier was checked with a transit instrument at frequent intervals during the pouring operation, and though its top is 30' above the ground level, it has since been found to he within one millimeter of its correct position The bearings have an adjustment of 1/2". The pier, with 8" reinforced concrete walls, is hollow inside, and this provides a 'strong box' on the first floor of the observatory.

"The polar axis is made of arc-welded steel plate instead of the usual castings. Two sectors were cut from a flat plate and rolled into cones. These are internally braced with fins welded in at the points of greatest stress. The larger ends of the cones are bolted to a cube of nickel-steel through which the declination axis passes at right angles. The unit is free from flexure and has five times the necessary strength. Each end is fitted with an 8", Timken, high-precision, tapered roller bearing. The 2000 pound counterweight is rigidly attached to the polar axis. The saddle in which the optical tube rests, is a standard 18" channel braced with a number of small fins welded in to make it rigid. The declination axis is a standard steel tube that permits the projection of the Cassegrain cone through it. The Cassegrain image may be observed only 2' from the center of rotation.

"Movement of the telescope is accomplished entirely by electric motors. These drive two large gears that contain some new ideas. The right ascension gear has a bronze tire shrunk on an iron center. It is 50" in diameter and has 400 worm teeth cut in the bronze. The 48" declination gear is made from the same pattern, but has a ring of internal teeth bolted to its side. The outside of this gear is machined and marked with a setting circle. Circles and gears are combined in the same piece. The declination gear is driven by two 1/20 h.p. motors working in unison and driving four pinions mounted in the stationary counterweight.

"The glass-enclosed drive (Figure 1) which controls the telescope in right ascension is simple, quiet, and all in one compact unit. Exposures of an hour at the 15' focus have been made, with no noticeable drift of the star from the cross-hairs. Worm gears are used throughout, to attain quietness. A 1/12 h.p. synchronous motor, shown at the right in this figure, drives the 50" R.A. gear (part of which shows at the extreme top in the illustration) through a differential and four reductions-8 to 1, which is built in the synchronous motor, 16 to 1, 50-1/2 to 1, and 400 to 1 at the large worm gear-to gain the sidereal rate. The small motor (center) turns the differential box in either direction and at any required speed, but when the differential is stationary the telescope does not noticeably depart from the ideal clock rate The differential is used only when special rates are desirable, such as exposing star trail checking plates or guiding on some object that does not have the sidereal rate.

"The motor shown at the left in Figure 1 is a 1/4 h.p., high speed setting motor which is thrown in and out of engagement by an automatic electric clutch located in front of it. The whole driving assembly was designed by C. D. Turner, V. E. Maier and A. F. Pittman. Dual controls are mounted on the floor of the observatory and on the observing platform. The accuracy of the drive is attained through the use of multiple thread worms. With these any desired ratio may be obtained. The second reduction in this train, for example, consists of a double-thread worm driving a gear with 101 teeth, providing a ratio of 50-1/2 to 1. The use of multiple thread worms seems to be a new idea-at least it was evolved independently in Indianapolis. Through a suitable choice of ratios, the clock rate was lengthened 25 seconds per sidereal day, to compensate for atmospheric refraction.

"The control panel, shown in the central illustration on page 347, has three knobs which control R.A., Dec., and dome movements. The variable speed, reversible, motors are controlled by rheostats driven by the control knobs. These enable the operator to set the telescope at high speed or to give it just a touch over a small angle. There are no manual locking devices, and the rheostats make it impossible to start the instrument with a jerk or to subject it to undue stresses.

The optical tube (Figures 2 and 3) is made entirely of Lynite, Alclad, and Zeppelin Tube-all aluminum alloys. The tube contains over 500 pieces, all drawn together by an ingenious arrangement of tension struts. Flexure has been adjusted out of the tube by adjusting the tension at the proper points. The chief advantage of the Lynite tube is its mobility and freedom from bulkiness. Inertia and momentum are reduced to a minimum and the drive consequently can handle it much more smoothly. Had it not been for the many weight-saving devices incorporated in the instrument, its moving weight would have been more than double its present value- 5200 pounds. All the accessory parts are made of aluminum or stainless steel, to eliminate troublesome rust which tends to occur in an unheated dome. The accessories, as well as the mounting, were all made by C. D. Turner.

"Figure 2 also shows the upper end of the telescope, with the plateholder used at the prime focus. The upper section of the tube rotates on adjustable Torrington needle bearings shown in the same figure and the Newtonian plateholder can be turned to any convenient position. Guide stars are sent to the small telescope mounted on the rim of the tube. The double-slide plateholder makes guiding convenient and simple. This device is to have a coma corrector installed, at the suggestion of Dr. Harlow Shapley, to flatten the field over the 4x5 plate. Figure 3 also shows a view down the tube. The curved sheet just above the aluminized mirror surface is a stainless steel cover which curves to the inside of the tube when it is raised, and straightens out again when it is lowered on the mirror cell. The cover has a chamois of the mirror is paint, applied to aid in collimation. The prime-focus plateholder can be seen reflected from the mirror's surface.

"Another piece of equipment that is different is the observation platform of the larger dome (Figure 4). Its design was evolved chiefly from Dr. E. F. Carpenter's platform at Steward Observatory, Tucson, Arizona. The chief difference lies in the method of supporting the load. This platform, which has a capacity of six persons, is supported by two long steel arches which span the inside of the dome on either side of the shutter opening. They stand on the dome's steel base ring, and are also strong enough to contribute to the support of the dome's wooden superstructure. The wooden platform floor is suspended from two straight tracks welded, like chords, to the arches at the correct incline. The platform, with its rollers, is pulled up and down these tracks by steel cables and a 1/2 h.p. motor. The hoisting mechanism is mounted in the upper part of the dome back of the opening. The dead weight of the platform is relieved from the hoisting a mechanism by a counterweight on the opposite half of the steel arches. The entire assembly is independent of the dome and would operate as well if it were standing by itself. It allows access to any point reached by the upper end of the telescope. There are no blind spots with this instrument. The switches and wires at the right, in Figure 4, operate the dome, platform and telescope. There are no wires on the telescope tube.

"The second, or small, dome (Figure 5) houses a 5" Zeiss triplet apochromatic refractor that matches the performance of instruments many times its size. This telescope has a full complement of accessories including those for solar work. The smaller dome is made in two halves, so that much of the sky may be seen at one time. One a half is just an inch smaller in radius than the other. This dome is framed of steel channels rolled to radius and welded into place. The inside of the dome is covered with Sprayoflake, a patent heat insulator, sprayed on with a hose. This keeps the interior comfortable during hot summer days.

"Except for the study room, which is well insulated and is heated electrically, the observatory building is not heated. It has its own water system and fire protection. The interior has hardwood floors, panelled knotty pine walls and beamed ceilings. A spiral staircase leads to the large dome and telescope, and a smaller stair to the other dome.

"The administration of the observatory has been invested in a non-profit corporation a called the Goethe and Helen Link Foundation for Scientific Research. Its purpose is to advance the science of astronomy in the state of Indiana. Dr. Link has endowed the observatory with a permanent income. Dr. James Cuffey, the first astronomer from Indiana University to hold the position of research fellow at the observatory, has already published work done with this instrument. Dr. B. C. Getchell, astronomer at Butler University, Indianapolis, uses the observatory, as do many teachers in central Indiana. Samuel Waters, who originally inspired its creation, is president of the Foundation. The writer, an Indianapolis 'TN' supervised and coordinated the work of construction, and is employed as director of the observatory.

"The builders of the observatory are indebted to the many members of the astronomical profession who have aided in its successful completion.

"All agree that the spirit of unique and co-operation created by Scientific American's two 'Amateur Telescope Making' volumes is chiefly responsible for the existence of the new Goethe Link Observatory. With regard to the mirror, about which another 2000 words might be written, a Hartmann test, reduced by Dr. James Cuffey of Indiana University, disclosed a 'Hartmann criterion' of .066 second. (Those who have memorized 'the book' will recall that this figure represents the least diameter of the cone of rays, approximately in seconds of arc, reflected from the mirror's surface.) This mark is but 0.016, second from the record set on the McDonald mirror. Greater accuracy is not necessary, as the inherent diffraction in the instrument enlarges the apex of the cone to twice this amount even with perfect atmospheric conditions. The mirror was aluminized by Leroy M. E. Clausing.

"The 8-1/2'' by 12" flat also was made by Charles Herman and V. E. Maier."

IN almost no time, after the publication of "ATMA," describing the Richest Field Telescope which shows the maximum number of stars possible in one field, these ''RFT's" were being made by the hundreds and everybody was acclaiming them as superlative. Most of these were of 6" size but Figure 6 shows a 12-1/2" RFT, the one nearer the reader, made by J. F. Simpson, a medical and X-ray technician at Garrison General Hospital, Gastonia, North Carolina, and set up on a roof. It is an f/5 and Simpson says it "shows most beautiful star fields, while the Orion nebula is more brilliant than I have ever seen it. When looking at the Moon, it is actually necessary to hold your hat over the mouth of the tube to cut down the superabundant light."

The other telescope, mounted tandem in a long yoke of corner-welded angle iron filled in with two-by-fours, is a 12-1/2" Cassegrainian. These two make just the right combination for non-contortionists: the Cassegrainian higher up and used from below, the Newtonian below and used from above. The tube of the RFT turns in the solid trunnion ring shown to place the eyepiece wherever most convenient.

Simpson formerly had the 12-1/2" Cassegrainian and an 8" RFT mounted in tandem on the same roof (described in the March, 1940, number) but each in a fork instead of a yoke. This lacked stability, but the double yoke affords great stability, he now testifies. Simpson's intention is to link the two tubes together with a rod (detachable whenever desired) so that they will always cover the same field.

OF side interest to "TN's" is a recent improvement in commercial silvering of ordinary looking-glass mirrors, developed by Peacock Laboratories, Inc., 54th St. and Paschall Ave., Phil., Pa., a Libby-Owens-Ford subsidiary. Old method was to wash the glass, go over it with tin chloride wash this off, lay the glass on a heated table and pour on, from a pitcher, the mixed ammonia silver nitrate-plus-reducing solution, using 8 oz. per sq. ft., and wait 20 to 60 minutes for the coating. New method employs a two nozzle spray gun. Emerging from it in a spray, the two solutions meet and mix 7" in front of the nozzle, and continue to the glass. The glass is sloped and moves on a conveyor belt, greatly speeding up the work. Claims are that 1 oz. silver nitrate silvers 30 sq. ft. of glass, showing how wasteful our telescope mirror methods must be-or were before aluminizing took the lead.

NEW clubs of amateurs: The Amateur Astronomer's Club, S. Rasmussen Cor. Sec., 720 Westover Ave., Norfolk, Va. Telescope Makers of Central California, Jos. A. Mello Sec., Suite 222, First Nat'l Bank Bldg., Madera, Calif.

The Society for Amateur Scientists (SAS) is a nonprofit research and educational organization dedicated to helping people enrich their lives by following their passion to take part in scientific adventures of all kinds.