The U.S. Naval Observatory acquired an 8.5-inch transit circle by made by Pistor & Martins in 1865, and used it to determine positions of standard and miscellaneous stars, the Sun and Moon, and major and minor planets. This filar micrometer was used at the eye-end of that instrument. It has horizontal and vertical screws and spider lines, as well as a set of Rogers levers so that several measurements can be made at one time and recorded later. These levers were designed by Joseph Addison Rogers (1840-1917), a young man who graduated from Yale in 1860, received a Ph.B. in civil engineering from Yale in 1861, and then went to work at the Naval Observatory.
Ref: “Modification of the Micrometer Head, devised by Mr. Joseph A. Rogers, Aid U.S. Naval Observatory,” Astronomische Nachrichten 63 (1865): 77-78.
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