Evening Star Newspaper, October 27, 1935, Page 84

2 Magazine Section THIS WEEK Photograph of the Great Nebula in Andromeda, courtesy Carnegie Institution This new type telescope scans the skies from the Naval Observatory New Eyes to the Stars Man peers into space, farther and ever Sfarther —how far will he wltimately see? The new 200-inch “eye,” now half completed, at one Sfell swoop will triple our- reach into the skies by GEORGE W. GRAY tributions of the 1930's to world progress, 1 wonder if he will rate anything as more important, more creditable to the genius of mankind, then our present activity in the building of great telescopes. Of course, he will know something of the vaster universe which is to be opened to view through these new optic glasses, and so will be able to weigh relative values more intel- ligently than we can guess at them now. But 1 venture to expect that such evidence will be outstanding — that the new “‘eyes” which we have fashioned in these depression years will turn out to be among America’s lasting and best-remembered gifts to civilization. The record thus far is an impressive one. Since 1920, large telescopes have been in- stalled at Harvard in Massachusetts, at Per- kins Observatory in Ohio, at the Naval Observatory in Washington, D. C., and at the University of Toronto in Canada. Optical workers are now grinding an 82-inch glass disk into.a concave mirror for the University of Texas: and a dome to house it has already been erected on Mount Locke, a 7500-foot peak in the picturesque Davis Mountains of the southwestern cattle ranges. Still in the -making is an 86-inch disc destined for the University of Michigan’s sta- tion near Ann Arbor. Capping the climax of all these efforts, and epitomizing in its huge undertaking this whole movement to reach deeper and farther into space, is the giant 200-inch reflector for the California Institute of Technology —a work of such magnitude that although it has been in progress for more than five years it is only half completed. HUNDRED YEARS from now, when the A historian comes to appraise the con- Two hundred inches is nearly 17 feet —so the mirror which will form the principal op- tical part of this supreme instrument will be nearly 17 feet in diameter. It must be ground into a concave surface such that its curvature represents that of a section of a sphere of 111 feet radius; and this curvature must be so perfectly figured that at no point is it off more than two millionths of an inch. The mirror must be rigid enough to support its weight without bending, and at the same time its mass must be kept as light as possible. Its material must be sufficiently heat resistant not to espand or contract with changes in temperature. All these conditions were uppermost in the, minds of those intrusted with the crucial task of finding the most practicable material for this use. Finally, after many tests and experi- ments, the experts developed a new glass of extreme toughness and low expansion, a re- finement of the well-known pyrex used for making cooking vessels. A disk was cast of this new material in March, 1924, but in the pouring certain of its lugs broke loose from the bottom of the mould and floated on the flood of bubbling liquid glass. So, to insure a perfect product. a second disk was cast last December without mishap. That second disk is now cooling in its anneal- ing oven in Corning. N. Y.-— the most precious piece of glass on earth. The glass was at 1200 degrees Fahrenheit when it was put to bed in the annealer on December 2. In order that the surface may not harden faster than the interior, and thus set up stresses and strains in the glassy struc- ture. its heat was permitted to seep away very slowly, at a rate somewhere around 2 degrees a day. Last August 21 the temperature was down to 638 degrees — considerably cooler, but still three times the heat of boiling water! Since then it has been allowed to cool more rapidly, and by early next month the glass should have reached room temverature. Then Photograph by Ayres A. Stevens The first 200-inch “eye” — next month the new one will be opened Copyright, 1935, United Newspapers Magazine Corporation October 27, 1935 Photograph by O. Struve An 82-inch “eye” will go into this dome in the Texas Mountains the annealing will be at an end, the walls of insulation will be removed and the disk will be exposed for inspection. In January it will be crated for shipment to California. Whether the journey will be made by rail or by water (via the Panama Canal) has not yet been decided. At last accounts, I believe, the com- mittee had figured that an underslung steel flatcar might be adapted to accommodate the huge steel crate, and a route was being worked out to avoid tunnels and overhead bridges and thus permit the shipment to be made by rail. In Pasadena, the Californians are all ready for it. They have built a spacious machine shop (a single high-ceilinged room 162 feet long by 54 feet wide) especially to care for the grinding, polishing and finishing of this glass and its accessory parts of the telescope. Years will be spent in the shaping of its surface, for even though the glass is of low response to heat, the friction of prolonged grinding would develop dangerous tempera- tures. So the grinding must proceed . piece- meal, in brief sessions, with generous resting periods between. The machine shop is com- pletely air-conditioned, to guard against float- ing dust and grit which might mar the process- ing, and also to insure constancy of #ir temperature and moisture. When the glass is optically right in cur- vature, it will be made into a mirror by coat-: ing its upper surface with a thin film of , aluminum. This use of aluminum in place of the usual silver is also a product of the de- pression years. Tests lately made at Lick Observatory and at Mount Wilson show that certain ultraviolet rays which are absorbed by silver are almost wholly reflected by aluminum —thus making it possible to deliver to the astronomical camera more light from the heavenly bodies, and so to photograph their images more sharply. The 200-inch mirror weighs 20 tons It is to be mounted at the lower end of a 55-foot skeleton tube of steel. This tube must be so rigid that it supports the weight of the mir- ror and accessory parts without bending and without serious friction. The load must be so (Continued on page 12)