Alvan Graham observed the eclipse of 22 December 1870 at Jerez de 

 la Frontera, Spain, again as a member of a Coast Survey party directed 

 by Winlock. His assignment was to help Winlock make spectroscopic 

 observations of the solar corona. A spectroscope was attached to the 

 above-mentioned 5^/2 -inch Harvard equatorial. Winlock watched the 

 spectroscope, while, in his words, "Mr. Alvan G. Clark, whose skill in 

 everything pertaining to a telescope insured careful and judicious man- 

 agement of the instrument, was stationed at the finder to direct the tele- 

 scope to the parts of the corona which were to be examined, and at the 

 same time to observe incidentally general phenomena." 10 ° Their results 

 were frustrated, however, by clouds. 



On 29 July 1878 Alvan Graham was at Creston, Wyoming, a member 

 of the United States Naval Observatory eclipse party organized by Wil- 

 liam Harkness. In cooperation with A. N. Skinner, he obtained six photo- 

 graphs of the corona, which were described as "at least as extensive and as 

 rich in detail as any ever taken." 101 They used a camera with a 6-inch 

 aperture Dallmeyer lens, supported on an equatorial mount pirated from 

 an instrument made by the Clarks for the 1874 Transit of Venus. 102 Tak- 

 ing these pictures was really a two-man operation. Clark guided the 

 camera and inserted and removed the sensitized plates; Skinner timed 

 the exposure with a sand glass and regulated the exposures via a black 

 wood fan with which he could cover the object lens. 103 George Clark de- 

 clined invitations to join expeditions to observe these latter two eclipses. 104 



The three Clarks working together made photometrical experiments 

 in 1862-63 in a unique way. 105 Their results for the sun and 

 moon were not far from accepted modern values, but their stellar 

 results were less reliable. Where others used a wedge or polar- 



100 U.S. Coast Survey Report, 1870, p. 140. 



101 Edward S. Holden, "Astronomy," Annual Record of Science and Industry (1878), 

 p. 21. 



102 See below, description of Transit of Venus apparatus, in catalog of Clark 

 instruments. 



103 U.S. Naval Observatory Reports of the Total Solar Eclipses of July 29, i8j8, and 

 January 11, 1880, p. 51. 



104 John A. Brashear, "George Bassett Clark," Astronomy and Astrophysics, vol. 12 

 (1893), pp. 367-372- 



105 Alvan Clark. "The Sun a Small Star," Memoirs, American Academy of Arts and 

 Sciences, vol. 8 (1863), pp. 569-572. See also Alvan Clark, "The Sun and Stars 

 Photometrically Compared," American Journal of Science, vol. 36 (1863), pp. 76-82. 



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