From Smart's "The Makers of Surveying Instruments in America since 1700":

- John J. Bausch and Henry Lomb, who immigrated from Germany in 1849, started their optical business in Rochester, NY, in the mid 1850's which eventually became the Baush & Lomb Optical Company and was first listed in the Rochester directory in 1873.

- George N. Saegmueller came to America from Germany in 1870. While working for the U. S. Coast & Geodetic Survey, he founded along with two brothers-in-law, Fauth & Co. which made astronomical and engineering instruments and was located in Washington DC. He later bought them out and changed the firm's name to George N. Saegmuller in 1900.

- "Bausch & Lomb Optical Co. merged with Fauth & Co. of Washington, of which George N. Saegmuller was sole owner in 1905. They continued making engineering instruments for some time after the close of World War I."

Basis the serial number of this instrument (6640), it was likely manufactured in 1907.  http://www.surveyhistory.org/how_old_is_my_bausch_&_lomb1.htm reports the number 6750 was used for instruments made after January 1, 1908.