The Washburn Observatory of the University of Wisconsin is 

 equipped with several Clark instruments. 262 Their equatorial refractor, 

 like that of the U.S. Naval Observatory (q.v. ) , well illustrates the quanti- 

 tative competitiveness of i gth-century observatories : the order for the tel- 

 escope specified that it be "larger and more powerful" than the great re- 

 fractor of the Harvard College Observatory ( q.v. ) . The Wisconsin instru- 

 ment, built in 1878, had an aperture of 15.56 inches and was provided 

 with eyepieces of various powers, a polarizing solar eyepiece, a 

 double-image micrometer, and a filar micrometer with bright-wire illumi- 

 nation. This last was designed by, and built for, S. W. Burnham, who 

 was then observing difficult double stars — that is, pairs of unequal bright- 

 ness, and pairs at the limit of the telescope's separating power. George 

 Clark produced an elegant micrometer in which the wires were sharply 

 defined and uniformly bright in all positions and which avoided stray 

 light in the field. The micrometer proved so successful that similar ones 

 were made for such instruments as the 26-inch refractor at the University 

 of Virginia and the 12 -inch at the Lick Observatory (qq.v.) . The Clarks' 

 equatorial mount for the Washburn telescope was not as successful as the 

 micrometer and optical parts; within twenty years it was found less con- 

 venient than more modern instruments. 263 



The meridian circle at the University of Wisconsin, made by Repsold 

 in 1 88 1, has a 4.8-inch Clark objective. When S. W. Burnham (q.v.) 

 went to Madison he took his 6-inch Clark refractor with him and sold it 

 to the university in 1882. 



The astronomical observatory of the Sheffield Scientific School at 

 Yale University was opened in 1866. Its equatorial refracting tele- 

 scope, from the Clark workshop, was said to perform in accordance 

 with the reputation of its makers. The achromatic objective had a clear 

 aperture of 9 inches and a focus of only 9 feet 1 o inches. The tube, which 

 was of stiff but light pine, was one of the last wooden ones made by the 

 Clarks. As in the instrument which had so impressed Dawes (q.v.), a 

 U-shaped iron piece supported the polar axis and protected the driving 



262 Publications, Washburn Observatory, vol. 1 (1882), pp. 23-30. See also Joel 

 Stebbins, "The Washburn Observatory, 1878- 1958," Publications, Astronomical 

 Society of the Pacific, vol. 70 (1958), p. 438. 



263 G. C. Comstock, "The Washburn Observatory," Publications, Astronomical 

 Society of the Pacific, vol. 9 (1897), p. 32. 



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