This micrometer for celestial photographs dates from around 1871. In use, the photographic plate was held horizontally and seen through two microscopes. For rectangular coordinates, the microscope is moved back and forth. For position angles, the plate and its bed are rotated. Some original parts are lost.
This was designed by Lewis Morris Rutherfurd (1816-1892), a wealthy New Yorker who made important contributions to astronomical photography and spectroscopy. It ended up in the observatory at Columbia University.
Ref: “Micrometer,” The American Cyclopaedia (New York, 1875), vol. 11, p. 512.
Deborah Jean Warner, “Lewis M. Rutherfurd: Pioneer Astronomical Photographer and Spectroscopist,” Technology and Culture 12 (1971): 190-216.
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