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Figure 18. — Improved telescope eyepiece which permits easy access to the 

 lenses for cleaning and repair, patented by Alvan Clark on 1 1 November 

 1 85 1. Drawing from patent papers. 



double stars, showed him objects "generally considered tests for 12 

 inches." 85 In 1880 the instrument passed to Charles P. Howard (q.v. ). 

 As pleased as he was with this instrument, Edgecomb was even more 

 enthusiastic about binocular telescopes. His largest pair of binoculars — 

 with prismatic eyepieces and twin objectives measuring 6^6 inches 

 each — were made at the Clark establishment in 1894. The prisms, of 

 exceptionally pure glass, were well figured. The focal lengths of the ob- 

 jectives — 94 inches — did not differ by more than a hundredth of an 

 inch; the focal lengths of a pair of 5-inch objectives, figured for Edge- 

 comb by Sir Howard Grubb, however, differed by ten times this amount. S6 

 According to Edgecomb, Alvan Graham took great pride in these bin- 

 oculars, but was reluctant to give credit where it was due. Writing after 

 the death of Alvan Graham, Edgecomb noted that "the whole work, I 



85 Edward S. Holden, "Astronomy," Annual Record 0/ Science and Industry (1877), 



P- 45- 



86 D. W. Edgecomb, "Reflectors," Popular Astronomy, vol. 2 (1894-1895), p. 370. 



61 



