Charles A. Young, professor of astronomy at the College of New Jersey (later Princeton University), acquired this diffraction grating in 1877. The speculum metal plate measures 2⅞ inches square, with the grating measuring almost 12 inches square. It is marked "Aug. 24, 1877; 5,760 per inch; 11,280 spaces, D. C. Chapman; 175, 2 Ave. N. Y." Daniel C. Chapman was the mechanic who operated the ruling engine designed and built by Lewis M. Rutherfurd.
Ref: D. J. Warner, "Lewis M. Rutherfurd: Pioneer Astronomical Photographer and Spectroscopist," Technology and Culture 12 (1971): 190-216.
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