Telescope (micrometer), ca. 1780
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Photo courtesy of Monticello/Thomas Jefferson Foundation, Inc.

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The micrometer or achromatic telescope has a double-refracting lens of Iceland crystal and fittings of brass; it is held in a pressed-board tube that is open at one end. The tube is covered in blue-green paper with a printed table or scale of measurements glued to it. The separate case has an outer laminated textile cover with a leather carrying handle or strap.

The Abbé Rochon worked and studied at the royal Cabinet de Physique at Passy, and was a neighbor of Franklin's. The instrument was described as "the micrometer of Monsieur Rochon" in Jefferson's papers, and also as a "telescope of Iceland crystal by the abbé Rochon & Herbage."

Monticello's website has a detailed description and photograph of the micrometer. Go to

Connection to Franklin
Given to Franklin by its inventor Terms of Use Credits