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.

The observatory and the great telescope which constitutes its central fact are to bear the name of the donor, Mr. Yerkes, of Chicago, who has contributed the means for rearing this magnificent adjunct of the University.  The enterprise contemplated from the first the construction of the most powerful telescope ever known.  The manufacture of the objective, upon which everything depends, was assigned to Mr. Alvan G. Clark, of Cambridgeport, Massachusetts, who is the only living representative of the old firm of Alvan Clark & Sons.

Alvan G. Clark has inherited much of the genius of his father, though it is said that in making the lens of the Lick Observatory the father had to be called from his retirement to superintend personally some of the more delicate parts of the finishing before which task his sons had quailed.  But the younger Clark readily agreed to make the Geneva lens, under the order of Yerkes, and to produce a perfect objective forty inches in diameter!  This important work, so critical—­almost impossible—­has been successfully accomplished.