basis of a photographic telescope. The tube, objective, and micrometer 

 of the old 9.6-inch aperture refractor, mounted inside the shortened 

 tube of the 26-inch equatorial, served as a guiding telescope. Photo- 

 graphs were taken with twin 6-inch Dallmeyer portrait cameras — like 

 that used by Alvan Graham Clark to photograph the 1878 solar eclipse — 

 mounted outside the large tube, and later with twin cameras with 10- 

 inch wide lenses. 238 In 1921 the weight-driven drive of the photographic 

 telescope was replaced by an electric one. 239 



Maria Mitchell, at Vassar College, called on the Clarks to make and 

 repair her astronomical instruments. The 12 */> -inch Fitz equatorial re- 

 fractor — which has recently been retired to the Smithsonian Institution 

 (q.v. ) — had a troublesome original objective and mount. In 1868, 

 shortly after it was installed, the Clarks reground the lenses to such a 

 degree that they considered this telescope one of theirs. Soon thereafter 

 they repaired the driving apparatus. 240 Warner & Swasey later completely 

 remounted the telescope. 



The smaller equipment of the Vassar observatory included a meridian 

 instrument by Young of Philadelphia, with two collimating telescopes 

 by the Clarks, 241 and two portable Clark refractors of 3 and 6 inches 

 aperture. 242 As early as 1871 Vassar students took pictures of the sun, 

 every day at noon, with a 2-inch aperture, non-achromatic, long focus 

 photographic telescope, similar to that used by Winlock at Harvard 

 (q.v.), and made by the Clarks. 243 The Vassar students had the use of 

 several other portable telescopes as well : the largest, a 5-inch Clark equa- 

 torial, belonged to Miss Mitchell (q.v.) . 



238 George Henry Peters, "The Photographic Telescope of the U.S. Naval Observa- 

 tory," Popular Astronomy, vol. 27 (1919), pp. 1-10. 



239 George Henry Peters, "The New Electric Driving Clock of the Photographic 

 Telescope of the U.S. Naval Observatory," Popular Astronomy, vol. 30 (1922), pp. 

 1 -10. 



240 Maria Mitchell, Observations with the 12-Inch Equatorial 13 April 1866- 

 12 June 1877, entries for October 1868, 18 August 1870, and 7 January 1871 

 (Manuscript copy in Vassar College Library). 



241 Edward S. Holden, "Astronomy," Annual Record of Science and Industry (1877), 

 P- 5i- 



242 The Vassar Transcript, February 1879. See also Mary W. Whitney, "Vassar 

 College Observatory," Publications, Astronomical Society of the Pacific, vol. 6 (1894), 

 p. 151. 



243 Alvan Clark & Sons to Simon Newcomb, 31 May [1871?] (letter in Newcomb 

 Papers at the Library of Congress). 



104 



