Provenance:John Hartwell Cocke; by descent to John Page Elliott; by gift and purchase to the Thomas Jefferson Foundation in 1992
Accession Number: 1992-4-2
Historical Notes: Jefferson's list of "Mathematical Apparatus" includes "a Telescope of Iceland chrystal by the abbé Rochon & Herbage."1 This "lunette," as he sometimes called it, combined an achromatic telescope with a prismatic micrometer, based on the use of double-refracting rock crystal.
Jefferson was in Paris while the Abbé Rochon was making his important new discoveries in optics at La Muette, the royal Cabinet de Physique in Passy. At Benjamin Franklin's house nearby, he had seen Rochon demonstrate his micrometer and had learned its principles from the inventor himself. "I was intimate with him in France," Jefferson wrote in 1812, adding that he possessed "one of his lunettes, which he had given to Doctor Franklin and which came to me thro' mr [Francis] Hopkinson."2 Later he lamented that Rochon's micrometer had not been widely adopted in navigation and land armaments, commenting that "it is one of the remarkable proofs of the slowth with which improvements in the arts & sciences advance."3
John Hartwell Cocke's known interest in Jefferson's scientific instruments suggests the possibility that Cocke acquired this micrometer from Jefferson's estate after his death.