Clark, Alvan

Alvan (1804-1887), a maker of astronomical instruments. With his son, Alvan G. Clark (1832-1897), he formed the firm of Clark and Son of Cambridge, Massachusetts, known the world over for telescopes of great delicacy and power. The more interesting of their telescopes may be mentioned. One, bearing an object glass with an aperture or diameter of eighteen and one-half inches, is owned by the astronomical society of Chicago. The Naval Observatory at Washington has a twenty-six inch Clark telescope. Cyrus McCormick, the maker of reapers, gave a large Clark to the University of Virginia. A thirty-inch instrument was made for the Imperial Observatory at St. Petersburg; a thirty-six inch for the Lick Observatory at Mount Hamilton, California, and lastly a forty-inch object glass was ordered by C. T. Yerkes for the University of Chicago Observatory at Lake Geneva, Wisconsin. The Yerkes lens is the most powerful in existence. It brings the moon within an apparent distance of a few miles from the observer. It requires the purest of glass and the work of years to bring one of these lenses to perfection. The finish is so delicate and so perfect that a single careless touch with the end of one's finger would ruin the surface and render the glass useful only for a smaller lens. See Telescope