A Huge Telescope.

Progress, Volume III, Issue I, 1 November 1907, Page 23

A Huge Telescope.

The huge telescope presented by the late Mr. Yerkes to the Williams Bay observatory is still the most powerful instrument of the kind extant, but a much larger telescope still is to be built for the solar observatory of the Carnegie Institution on Mount Wilson, in California. This telescope, for which the funds are being provided by Mr. John D. Hooker, of I,os Angeles, is to be of the reflecting type ; and some idea of the immense stride in telescopic construction, which will be made by this new addition to the astronomer's resources, may be gathered from some notes supplied to Engineering by Professor Hale, of the observatory on Mount Wilson. The largest reflector hitherto made has a 60in. diameter silvered - glass mirror, of which the glass has a thickness of Bin. and weighs one ton. In the proposed new telescope the mirror will be lOOin. in diameter, necessitating a thickness of glass of 13in. s and a weight of four and a half tons. The Herculean task of casting and annealing this huge mirror has been entrusted to the Plate Glass Company of St. Gobain. The equally formidable task of grinding, figuring and testing will be undertaken in the workshops of the observatory itself, under the direction of Professor Ritchey ; and lastly, the mounting of the instrument is to be entrusted to the Union Ironworks Company, a firm which is well known as the builders of battleships and cruisers for the American Navy. It is estimated that the making and mounting of this telescope will take about four years. The question of its behaviour when finished will arouse considerable interest, for, undoubtedly, if its performance be satisfactory, it will be a great gain to astronomy. Its huge aperture, combined with comparatively short focal length, will make it extremely valuable for spectroscopic work of the fainter stars ; but as telescopes of increasing size are taken into usevery great difficulties are encountered.

The question of temperature is a grave one, for a very slight difference in the warmth of the air in one part of the tube will spoil the chances of successful observation. In the case of this new telescope, it is proper- i to keep the observatory always at one constant mean temperature, as near as possible to that of the night.