Object notes Associations
Jaw micrometer. Unsigned. Transferred from the U.S. Naval Observatory.
This is one of eight identical instruments made for the eight American parties sent to observe the Transit of Venus in 1874. Made by either Stackpole & Brother of New York or Alvan Clark & Sons of Cambridgeport, Massachusetts, they were used to measure the distance between the lens and the photographic plate, thus ensuring that the plate was precisely in focus. This particular instrument was used at Kerguelen in 1874 (by the party led by Commander George P. Ryan) and at Santa Cruz, Patagonia in 1882 (presumably by the photographer, William Bell). With the vernier, this instrument can measure to .01 inch.
Catalog no. 327,708 Physical Sciences Collection, Smithsonian Institution
Object contributed by National Museum of American History, Smithsonian Institution