Shortly after the installation of the Pistor & Martins meridian circle in 

 1865 the Clarks reworked most of its optical surfaces: the collimator 

 lenses, the eyepieces, and the 8^4-inch objective. When, along with all the 

 other instruments, the meridian circle was renovated for removal to the 

 new observatory, the Clarks made two new objectives for it. The first, 

 ground on the Littrow curves, had excellent definition only near the 

 optical axis. The second, and more successful glass, was of 9.14 inches 

 aperture and had curves computed by William Harkness. 230 



As early as 1869 astronomers outfitted by the Naval Observatory used 

 Clark portable equatorials for eclipse observations. These were usually of 

 3 inches apertures and 48 inches focus. Observers who were given, or used 

 their own, instruments by other makers frequently kept their remarks 

 about them to a minimum ; observers using Clark telescopes, on the other 

 hand, often named the opticians and praised their instruments. 231 



Although more inclined to precise measurement than to descriptive or 

 astrophysical researches, the Naval Observatory did purchase several ex- 

 perimental, long focus, photographic telescopes from the Clarks. 232 Their 

 first photographic apparatus, modeled after Winlock's equipment at Har- 

 vard (q.v.), was for use during the 1870 solar eclipse. Later ones helped 

 determine the American method of observing the Transit of Venus (q.v. ) . 



The great Washington equatorial — the 26-inch refractor of the U.S. 

 Naval Observatory— was the second largest-ever Clark instrument, and 

 the one which made the Clarks popular heros. The Dearborn refractor 

 (q.v.) had been completed in 1863 and, owing to the war, received little 

 public attention; however, the daily progress of the Washington telescope 

 was publicly noted. The Dearborn instrument had been so thoughtlessly 

 enclosed in a college tower that its potential could seldom be realized. Not 

 so the Washington instrument; and the discovery of the satellites of Mars, 

 during the opposition of 1877, demonstrated to all the power of this tele- 

 scope. 233 



The Washington telescope was proposed with the Clarks in mind. 

 While calling attention to their lack of a suitable instrument, the Wash- 



230 Publications, United States Naval Observatory, vol. 1, 2nd ser. (1900), pp. viii-ix. 



231 See U.S. Naval Observatory Reports of Observations of the Total Eclipse of the Sun , 

 August 7, i86g, p. 27; and U.S. Nautical Almanac Reports of Observations of the Total 

 Eclipse of the Sun, August 7, 1869, pp. 21-22. 



232 See correspondence between B. F. Sands and Alvan Clark & Sons, 1870-1872 

 (letters in U.S. Naval Observatory Papers, National Archives, Record Group 78). 



233 Simon Newcomb, Reminiscences of an Astronomer (Boston 1903), pp. 128-144. 



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