spent a lot of time in Cambridgeport, conferring with the Clarks on 

 the details of the instruments. After several of these visits Young wrote 

 articles— often for the Boston Journal of Chemistry — describing the work 

 in progress at the Clark factory. 



Shortly after his appointment to the college faculty in 1866 Young 

 ordered a $350 spectroscope from the Clarks. 46 Although frequently 

 modified, this instrument was in use until 1963; it is now preserved in 

 the Dartmouth College Museum. Young used this spectroscope during 

 the total solar eclipse of 1 869 for his observations of the recently found 

 green coronal line, and his discovery of a spectroscopic method of 

 determining the moment of contact between sun and moon. As his 

 observations might not have been possible with an instrument of lower 

 dispersion, Young carefully described his apparatus. The spectrum was 

 formed by a train of five heavy flint glass prisms of 45 ° each; and the 

 prism box could be adjusted for position of best definition for the various 

 lines. For comparison, a spark spectrum could be thrown into the field 

 of view. The collimator and eye telescope were of 2 54 -inch aperture and 

 16/2-inch focus. The eyepiece was provided with a micrometer for 

 determining the position of new lines. Finally, the whole spectral ap- 

 paratus was attached to a small comet seeker and equatorially mounted. 



Upon his return from the eclipse expedition Young designed, and 

 asked the Clarks to make, another spectroscope. 47 George Clark did most 

 of the work on this instrument and suggested several convenient adjust- 

 ments. This spectroscope had the dispersive power of 1 3 prisms of heavy 

 flint glass, yet was light enough to be attached to Dartmouth's 6.4-inch 

 German equatorial. Light from the slit and collimator passed through 

 the lower portion of 6 prisms and one half prism; it was then reflected by 

 a 90 ° prism back through the upper portion of the prism-train to the 

 observing telescope, which was above and parallel to the collimator. 

 One of George Clark's contributions was a new method of adjusting the 



46 Charles A. Young, "On a New Method of Observing Contacts at the Sun's 

 Limb, and Other Spectroscopic Observations During the Recent Eclipse," American 

 Journal of Science, vol. 48 (1869), pp. 370-378. See also the same author's "On a 

 New Method of Observing the First Contact of the Moon with the Sun's Limb at 

 a Solar Eclipse by Means of the Spectroscope" and "Spectrum Observations at 

 Burlington, Iowa, during the Eclipse of August 7, 1869," Proc, American Association 

 for the Advancement of Science, vol. 18 (1869), pp. 82-84, 78-82. 



47 Charles A. Young, "A New Form of Spectroscope," Journal, Franklin Institute, 

 vol. 60 (1870), pp. 331-334- 



49 



