PLUMBING SPACE

Evening Post, Volume CXXIV, Issue 61, 9 September 1937, Page 23

PLUMBING SPACE

GIANT NEW TELESCOPE

MAGNITUDE OF PREPARATION

YEARS OF LABOUR

The human erys, although adapted for terrestrial purposes, is of little use for critical examination of celestial objects without optical aid, and had it not been for the invention and subsequent improvement of astronomical telescopes our knowledge of the great universe around us would be very limited indeed, says a writer in the "News Chronicle." Although astronomy is one of the oldest of the sciences, telescopes have been in use for only a comparatively short time —a little over three centuries. The great Italian astronomer Galileo, although he did not invent the telescope, appears to have been the first to make and use it for astronomical purposes; and about the year 1610 observations made by him with his tiny instruments revealed for the first time the truth regarding the general structure of the solar system and the movements of its constituent members. Great advances have been made in the construction and size of telescopes since the time of Galileo. -The giant telescope on Mount Wilson, California, known as the Hooker Reflector, with a mirror lOOm in diameter, completed in 1916, is at present the largest in the world, and with it photographs can be taken of distant objects, the light from which takes several hundred million years to reach us. A U.S. MOVEMENT. It is, however, oy no means certain that even the largest telescopes at present in use have reached the boundaries, if any, of the great superuniverse of which our system is only a unit, and so, with the object of peering still further into space, a movement was started some yearsago in the United. States of America to construct a telescope with a mirror 200 in in diameter, and astronomers the world over are looking forward with intense interest to jts completion. The first, and probably the major, problem was the successful casting of a flawless glass disc 16Jft in diameter and 2ft thick. This, however, was safely accomplished at the Corning Glass Works, near New York City, on December 2, 1934, when nearly twenty tons of white-hot molten glass at a temperature of 2800deg Fahrenheit was ladled into the specially-designed disc-shaped mould. It was then left in an annealer for twelve months, the temperature meantime being gradually lowered. On December 8, 1935, the huge disc, the largest single piece of glass ever cast, was removed from the annealing chamber, and in March, 1936, it was sent across the. States to California. Transport presented a problem, but this was overcome with the assistance of several railroad companies, who provided a special train with a speciallybuilt underslung truck to carry the disc, which was kept upright in a steel crate. The train travelled at 'only 25 miles per hour and only during daylight, and great care had to be exercised to ensure sufficient clearance in tunnels, etc.. The journey took fifteen days. LONG POLISHING PROCESS. The glass now lies in the workshops of the California Institute of Technology, where the long and tedious process of grinding and polishing is proceeding as quickly as possible. This work, however, will not be finished for two or three years—it may possibly be more. Progress is necessarily slow, because the polishing raises the tempera.ture1 of the surface of the disc. and therefore cannot be • continued for more than very short periods—not more than an hour at a time; and it may be perhaps a full day before tests can be made and the work resumed. About four tons of glass will be removed by the hollowing process, and the final result will be a 200 in disc parabolic in shape and true to within one-millionth of an inch over its entire surface. Instead of "silvering" the surface a thin film of aluminium willbe deposited to give the necessary reflective power. Aluminium has been found to have distinct advantages over silver, besides increasing reflective power by about 50 per cent. The 55ft steel tube of latticed design, at the bottom of which the mirror will be mounted, will weigh nearly 100 tons, and the huge mounting or yoke qf welded steel which will hold the telescope and allow it to swing is any direction will weigh about 280 tons. In addition to the 200 in mirror there will be several auxiliary mirrors, also a spectograph and other. accessories; but it is interesting to. note that observers using the prime focus will be working in a specially-built cylindrical chamber at the top of the tube, practically inside the telescope. Access will be by way of an adjustable platform from the side of the dome. The total weight of the entire telescope and mounting will be nearly 450 tons. THE CHOSEN SITE. The site finally chosen for the telescope is Mount Palomar, which is about 6000 ft high, and is situated 85 miles south of the Mount Wilson Observatory, and some 50 miles north of San Diego City. The main observatory building and dome, will be 135 ft in diameter and about the same distance from the ground to the top. Provision is also being made for dark rooms, library, and staff quarters, as well as storage tanks for water and gasoline, and a pumping and distributing plant. Simultaneously with the fashioning of the mechanised parts of the telescope and the grinding and polishing of the Hiirror construction work on the buildings on Mount Palomar is being carried on, and it is hoped that by about the end of 1940 the whole scheme will be completed. The prime mover behind this huge scientific undertaking is Dr. George Ellery Hale, a former director of Mount Wilson Observatory. - He has for years been working for its accomplishment, and is at present chairman of the council in .charge of the project. The supervising engineer is Captain Clyde S. McDowell, of the United States Navy, who has been "lent" to the California Institute of Technology by the United States naval authorities. The total cost is estimated at £1,500,000, which will be *ound largely, if not wliblly, by wealthy scientific and philanthropic institutions of America. REVELATIONS IN PROSPECT. During the past few decades astronomical science has made wonderful progress, and completion of the 200 in telescope will add considerably to our present knowledge, not only of the universe, ofWhich the solar system is a member, but of the hundreds of thousands of other distant objects known as extra-galactic nebulae, many of which are now considered to be stellar systems comparable to our own. As the new telescope will be able to penetrate about three times as far as the largest one at present in use (lOOm telescope at Mount Wilson) the boundaries of space will be pushed out to an almost unthinkable extent, and, unless it. is found that there is a "thinning out" of the extrargalactic nebulae as distance increases, the 200 in | telescope will be able to detect faint objects, the light from which, travelling at a velocity of 186,300 miles per second, takes 1,200,000,000 years to reach us.