We cannot here refer to more than a few of the principal products of Clark & Sons. Gradually they extended the width of their lenses, gaining with each increase of diameter a rapidly increasing power of penetration. At last they produced for the Royal Observatory of Pulkova a twenty-seven-inch objective, which was, down to the early eighties, the master work of its kind in the world. It was in the grinding and polishing of their lenses that the Clarks surpassed all men. In the production of the glass castings for the lenses, the French have remained the masters. At the glass foundry of Mantois, of Paris, the finest and largest discs ever produced in the world are cast. But after the castings are made they are sent to America, to be made into those wonderful objectives which constitute the glory of the apparatus upon which the New Astronomy relies for its achievements.
It was in the year 1887 that the Lick Observatory on Mount Hamilton, of the Coast Range in Southern California, was completed. The lens of this instrument is thirty-six inches in diameter. Nor will the reader without reflection readily realize the enormous stride which was made in telescopy when the makers advanced from the twenty-seven-inch to the thirty-six-inch objective. Lenses are to each other in their power of collecting light and penetrating apace as the squares of their diameters, and in the extent of space explored as the cubes of their diameters.
The objective of the Pulkova instrument is to that of the Lick Observatory as 3 is to 4. The squares are as 9 is to 16, and the cubes are as 27 is to 64. This signifies that the depth of space penetrated by the Lick instrument is to that of its predecessor as 16 is to 9, and that the astronomical sphere resolved by the former is to the sphere resolved by the latter as 64 is to 27--that is, the Lick instrument at one bound revealed a universe _more than twice as great_ as all that was known before! The human mind at this one bound found opportunity to explore and to know a sidereal sphere more than twice as extensive as had ever been previously penetrated by the gaze of man.
Nor is this all. The ambition of American astronomers and American philanthropists has not been content with even the prodigious achievement of the Lick telescope. In recent years an observatory has been projected in connection with the University of Chicago, which has come almost to completion, and which will bear by far the largest telescopic instrument in the world. The site selected for the observatory is seventy-five miles from the city, on the northern shore of Lake Geneva. There is a high ground here, rising sufficiently into a clear atmosphere, nearly two hundred feet above the level of the lake.