prisms to their angle of minimum deviation, which depended upon 

 altering the circumference around which the prisms stood. If not theo- 

 retically exact, this method, according to Young, was simple and solid 

 and worked well. Young took this spectroscope to Spain for the 1870 

 solar eclipse, where he discovered the reversing layer of the sun. After 

 the eclipse Young had the Clarks remodel this spectroscope to incorporate 

 further improvements. He then thought this spectroscope inferior to very 

 few then in use, and as optically perfect as any he had ever seen. 48 The 

 spectroscope has since been retired and is on exhibit in the Dartmouth 

 College observatory. (See fig. 19, p. 64.) 



Dartmouth College, during Young's tenure, also acquired a Clark 

 equatorial refractor. The 9.4-inch objective was ground according to 

 Littrow's curves — i.e., a nearly equi-convex crown lens and a nearly 

 plano-concave flint. According to Young, the spherical aberration was 

 very perfectly corrected; the chromatic aberration was a little under- 

 corrected, a pleasant contrast to the overcorrected Munich lens he had 

 been using. 49 The tube was one of the earliest composed of plates of steel 

 riveted together. The telescope was remounted and provided with a 

 photographic correcting lens by the Alvan Clark & Sons Corp. around 

 i 9 o8. 50 (Seeng. 20, p. 89.) 



The first astronomical observatory in California was erected by George 

 Davidson in 1879 in LaFayette Park, San Francisco. 51 Its main instru- 

 ment was an equatorial refractor, with a 6/ 2 -inch Clark object-glass, and 

 a Fauth mount. Fauth & Co. had exhibited this instrument at the 1876 

 Centennial Exhibition in Philadelphia, where it won a gold medal. This 

 telescope has recently been given to the California Academy of Sciences, 

 of which Davidson was president for 1 4 years. 



William .Rutter Dawes, the Clarks' first important customer, was 

 an innovative observer who would rather order new instruments than 

 modify old ones. According to Simon Newcomb, "Mr. Clark, not being 



48 Charles A. Young, "The So-called Elements," Knowledge, vol. 1 (1881), pp. 

 151-152- 



48 Charles A. Young, "The Color Correction of Certain Achromatic Object- 

 Glasses," American Journal of Science, vol. 29 (1880), pp. 454-456. 



50 John K. Lord, A History of Dartmouth College, 1815-igog (Concord, N.H., 1913), 

 pp. 609-610. 



51 "George Davidson," Dictionary of American Biography (New York, 1930), vol. 5, 

 p. 92. 



50 



