IN STARRY SKIES

Evening Post, Volume CIX, Issue 33, 8 February 1930, Page 15

IN STARRY SKIES

G. W, RITCHEY

GREATEST LIVING MAKER OF

TELESCOPES

(By "Omega Centauri.")

Last week we gave a very brief sketch of the development of the telescope from the tiny instruments of Lippcrshey and Galileo to the giant reflectors of Mount Wilson and Victoria, B.C.- We saw that progress came in a series of waves, each iv turn checked by an obstacle which appeared for the time quite insurmountable. Galileo quickly increased the magnifying power «f his instruments from 3 to 32 dia-

m6ters, but as the power increased' the ield of view became inconveniently email. Kepler, by changing the eyepiece from a concave to a convex form, secured high magnification with a reasonably large, field, but spherical and chromatic aborrations became more »nd more troublesome. Descartes showed :that spherical aberration could be minimised by making the object glass yejy .thin,"and of long focus. This led to the. construction of instruments that were too long to use successfully. Attention was then turned to mirrors in-

•teftd of lenses, and Gregory, Newton, and Cassegrain invented their types of reflecting telescopes. Opticians of sufficient genius and skill were not iinMediately forthcoming to make use of? these inventions, and half a century passed before Hadley made a really efficient, reflector. After another halfcentury the experiments were begun, ■which in a few years were to change the reflecting telescopes from little more than a toy to one of the most powerful instruments of research. But ■the systems of mounting were still-, so crude that observing was a. difficult feat, and the metallic reflectors needed constant attention. All the skill, the enthusiasm, and the indefatigable "energy of such men as the Herehels, Lord Bosse, Lassell, and Common, were: required to carry on research with, such! instruments. The mounting of giant telescopes is an engineering problem ■which has now been solved completely, and such devices as block and tackle hive been replaced by electric control. At the same time, the,metallic mirror has disappeared. Now.that the coating! of pure silver is deposited on glass,, a great mirror can be quickly and'easily recoated. These improvements have

made possible the marvellous discoveries of modern astronomy. But ; once more a limit seemed to be' imposed. Glassrnakers, withifall their skill and resources, found it impossible to east flawless discs of the size that astronodemanded. /It seemed as if the Hooker telescope, with its mirror, 101 inches in diameter, would be allowed to hold the record indefinitely. But it is not to bo so. Its supremacy is definitely challenged from two directions. Plans aro well advanced for a 200 in telescope under the auspices of the Carnegie Institute of Technology, and the Mount Wilson Observatory. In this instrument the final grinding and figuring of the surface of the mirror is to be done on a coating of pure silica that has been sprayed on to a fused quartz disc. In France, Professor G.. W. Ritchey is attacking the problem in quite a different way. As single discs of the size he requires cannot bo cast, he is building them up of plates of specially selected glass. The thrilling story of how it is done and what may be expected when the instruments arc completed,'has been told in "L'Astronomie," in the "Journal of the Eoyal Society of Canada," and in other publications. Professor Eitehey's experience is absolutely unique. It is as if a number of personalities, each endowed with unusual aptitudes, were combined in a single being. He is an origi inal inventory able to devise new instru[ments and new types of building. He is a skilled optician, who can figure giant mirrors with astounding precision. He ia a great astronomer, who can form a mental picture of an obscure problem that awaits solution. He can then construct tho requisite instruments, formulate the methods of research, carry out all the necessary observations, and interpret tho results. He does not specialise in one single science, he sees that success is dependent on the cooperation of several. A mirror 2u feet in diameter requires an enormous building, and ponderous mounting. Tho help of mathematics is invoked, new curves are calculated, and an instrument is devised, one-third of the original length, whilst retaining all the power and other advantages sought. He finds the enlargement of astronomical photographs limited by the grain of the iiJui. He carries.out extensive researches in the chemistry of photography, and produces films which will stand far higher magnification. He possesses not only original genius, but, also its other form, an infinite capacity for taking pains.- The photographs he has taken of spiral nebulae are a revelation. To prevent minute wanderings of the iniage on the plate, the telescope has to be guided sometimes for a dozen hours. The seeing varies from' one moment to another. When minute disturbances in the atmosphere impair the definition, the light must be instantaneously cut off, or the image on the film will be spoilt. The plate must be adjusted from time to.time to keep the focussing true, and all slight irregularities of the driving clock must be i corrected. In such work Professor Eitchey showed from the first an aptitude that was almost uncanny, but... he

wasn't satisfied, and so he invented instruments with' which he could practise the requisite motions during the day, to increase still' further the expertness of his manipulation during the critical hours of exposure in the night. We have seen many of the results he secured at Yerkes and at Mount Wilson,' but we must remember that a newspaper reproduction can give but a faint idea of the excellence of the original. No one knows better than Professor Bitchey the nature of the problems that have now to be solved, anil the difficulties that must bo surmounted. Hi? predictions have been vorified In the past, lie had faith in the possibilities, of the reflector when, others condemned it, and he showed what can be done, using the mirrors that he himself figured, the 24-inch .at Yerkes, and the 60-inch at Mount "Wilson. . The hundred-inch, which is now showing the wonders of distant space, is a further monument to his faith, skill, and perseverance. "We'can therefore hardly fail to be thrilled by the glowing picture he has painted' of the possibilities of the Bitchey-Cretian reflector, with a mirror six metres, or 19.7 feet, in diameter. , , ..'..'..