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New Colossus of Telescopes

By Paul P. Foster

In no branch of science is general interest greater, when the popular mind is directed to it, than in astronomy. The idea that we shall at some time find that other planets besides our own are inhabited and that we may eventually communicate with creatures upon those other worlds is always a fertile subject for thought. The hope of making some new step in advance toward this end is deeply stirred at news of such an undertaking as the building of a new telescope, the proportions of which are far greater than any previously constructed.

NE hundred inches or in round numbers, eight feet, is the astounding diameter of what will be the greatest telescope in the world. It will be an American instrument and is to be erected on the summit of Mount Wilson, in Southern California, as soon as it can be constructed. This remarkable telescope has been carefully planned and funds for its construction have been provided by the generosity of John D. Hooker, of Los Angeles, who, so far as is known, is the first man to cooperate with Mr. Carnegie in the latter's efforts for the advancement of science.

As readers of THE TECHNICAL WORLD may recall, the Solar Observatory on Mount Wilson is supported by the Carnegie Institution and is the newest and loftiest astronomical observatory in the United States. It is situated on the summit of Mount Wilson, six thousand feet above the sea, and not far distant from the

cities of Pasadena and Los Angeles. The observatory was established in 1904 for the special purpose of studying the sun, and the problems of solar and stellar evolution. After a long and careful investigation of possible sites, it was found that the conditions on Mount Wilson were almost ideal for solar observations, and the directors of the Carnegie Institution have made ample provision for the establish

JOHN D. HOOKER, DONOR OF 100-INCH LENS.

ment and for the maintenance of the observatory, during at least ten years, the length of a "sun-spot period."

Two unique telescopes have been in constant use at the observatory since its establishment. The larger is the Snow telescope, a reflector, which has been employed in daily observations and investigations of solar phenomena. A five-foot reflecting telescope has been completed and will soon replace the Snow telescope, when the Solar Observatory will be provided with the largest and finest reflector for solar purposes

yet constructed.

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The other important instrument is the Bruce photographic telescope which is designed exclusively for photographing the stars and nebulae. Very wonderful photographs of the stupendous star clouds of the Milky Way have been obtained with this instrument and the exceptionally transparent atmosphere at Mount Wilson makes it possible to photograph some of the best diffused nebulosities, which are obscured by the denser air at lower levels.

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To this observatory has been offered a telescope which will enable us to penetrate seven times farther into space than can now be done with the greatest visual telescopes. Its cost will be about onetwentieth of that of a modern battleship. The donor's deed of gift is as follows: Mr. George E. Hale, Director of the Solar Observatory, Pasadena. Dear Mr. Hale:

I hereby give and place at the disposal of the Carnegie Institution the sum of fifty thousand dollars, or so much of this amount as may be needed, payable on demand as the

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THE SUN ECLIPSED BY THE MOON-SHOWING CORONA.

The mirror of this telescope will be thirteen inches thick, will weigh four and onehalf tons, and four years will be required to make the glass and finish the optical work upon it. The glass will be constructed at the great French optical works in St. Gobain, and the difficult operation of figuring, i. e., grinding and polishing, will be under the supervision of Prof. G. W. Ritchey, at the instrument shops in Pasadena.

The possibilities of

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this greatest instrument of the age are concisely and comprehensively described in the following letter from Prof. Ritchey to the donor which was published in the Los Angeles Evening News, Sept. 15, 1906:

Solar Observatory Office, Pasadena, Cal.
July 27, 1906.

Mr. John D. Hooker, Los Angeles.
Dear Mr. Hooker:

I have your letter of July 26, in regard

flector, with silvered glass mirror and with with a well-designed mounting, may justly be regarded as the most modern and efficient type of telescope.

It should be remembered that a reflecting telescope gives superb views of celestial objects visually, also, but it is in photography that it is incomparably efficient, and it is here that results of the greatest scientific value will be obtained. First: An eight-foot reflector, which should have a principal focal length of fortyeight feet, would give revolutionary results in the photography of the nebulae. This is the subject in which I am personally most interested. My photographs of nebulae made at the Yerkes Observatory were obtained with the two-foot reflector, which had a focal length of only ninety-three inches. The eight-foot reflector would have a focal length of forty-eight feet, or 576 inches, that is, six and one-fifth times as great as that of the two-foot reflector; the scale or size of the photographs would be in the same proportion; and with the smooth motion of the telescope given by mercury flotation, together with the

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FIVE-FOOT MIRROR OF NEW 60-INCH REFLECTOR.

to the field of usefulness of an eight-foot reflector. The chief uses to which we would put such an instrument are briefly described below. You will note that all of these, except the measurement of the heat of stars, relate to photography. The reflecting telescope is especially efficient in photography, because of its perfect achromatism and also. because of its great speed, since the percentage of light lost by reflection at the silver film is much smaller than that lost in passing through the lenses of a large refractor. By far the most promising lines of advance in astronomical investigations are in the direction of photography; hence a great re

fine atmospheric definition and transparency to be had on Mount Wilson, we could certainly expect a proportional gain in the minuteness of detail and structure shown in these nebulae.

The great majority of the nebulae are small and faint-too small for such instruments as the two-foot reflector at the Yerkes Observatory, or even the Crossley reflector at the Lick Observatory. In fact, there are probably not more than forty or fifty nebulae which are sufficiently large for the best results with instruments of the scale of those just named, while the eight foot reflector would give us photographs of tens of thousands of

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Aggregations of stars appear in all parts of the heavens, but this is the most complex and extensive of all the gatherings of the stars.

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A part of the zone-shaped regions surrounding the whole sphere of the heavens, in which stars innumerable so combine their lustre as to present a milky luminosity.

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