purchased a 71/2-inch equatorial refractor from the Clarks for $1150. 

 Owing to their limited budget they had to choose between graduated 

 circles and a driving clock — either of which cost an additional $500. 2 

 Apparently, they found money for both. 



In 1888 Albion College, in Albion, Michigan, built an astronomical 

 observatory for the use of its students. The equipment included an 8- 

 inch aperture Clark refractor which was equatorially mounted and pro- 

 vided with driving clock, divided circles, and filar micrometer. 3 



By 1866 the Clarks had supplied Allegheny College, in Meadville, 

 Pennsylvania, with a 7-inch refracting telescope which, although equa- 

 torially mounted, was not equipped with either graduated circles or clock 

 drive. 4 



Allegheny Observatory of the University of Pittsburgh used the 

 Clarks' services during the 1870's; thereafter they relied on the local 

 and talented John A. Brashear. The 13-inch Fitz lens of the Allegheny 

 equatorial was stolen and slightly damaged in 1872. After its recovery 

 the Clarks refigured it, making it, in terms typically used to describe 

 Clark lenses, 'Tun des meilleurs objectifs de cette dimension que Ton 

 connaisse." 5 They also made a 4-inch photographic correcting lens which 

 was used in conjunction with the 13-inch. Samuel Pierpont Langley, 

 then doing solar physics at Allegheny, was using spectroscopic apparatus 

 too heavy to be easily moved; to convert the equatorial into a heliostat 

 the Clarks made a 12-inch diameter silvered plane mirror.* 3 Other Clark 

 instruments at Allegheny included a 3-inch objective lens 7 and a rock 

 salt prism identified as having been figured by George Clark. s 



The American Academy of Arts and Sciences in Boston owned 



2 Mary Delcher of Abbot Academy to Maria Mitchell, 2 April 1872 (letter in 

 library of Maria Mitchell Association). 



3 Tear Book of Albion College for i888-8g, p. 138. 



4 Elias Loomis, Practical Astronomy (New York, 1866), 7th ed., pp. 496-497. 



5 Charles Andre and A. Angot, V Astronomie pratique et les observatoires en Europe 

 et en Amerique. Part 3: Etats-Unis d' Amerique (Paris, 1877), p. 126. 



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

 p. 38. 



7 Alvan Clark & Sons to Samuel P. Langley, 5 November 1900 (letter in Smith- 

 sonian Institution Archives). 



8 John A. Brashear, "A Practical Method of Working Rock Salt Surfaces for 

 Optical Purposes," Proceedings, American Association for the Advancement of Science, 

 vol. 34 (1885), p. 76. 



40 



