This precise level is marked "J. Kern Aarau" and "U.S.C.&G.S. #36." It has a high-power inverting telescope and a delicate striding bubble level. A mirror above the level lets the observer read the bubble with one eye while sighting the rod with the other. A micrometer screw under one wye permits fine adjustments.
This was made by J. Kern of Aarau, Switzerland, whose precise levels had been recommended by the International Geodetic Commission in 1864. To enhance his position in the American market, Kern mounted a display at the Centennial Exhibition held in Philadelphia in 1876. This example was made after 1878, when the U. S. Coast Survey became the U. S. Coast and Geodetic Survey, and before 1889, when J. Kern began trading as Kern & Cie.
Ref: Randall Brooks and Heather Bajdik, "Precise Levels in Surveys of North America," Rittenhouse 10 (1996): 48-57.