Telescope

Telescopes for use by sailors and naturalists began to appear during the 16th and 17th centuries.
This monocular optical instrument allowed them to see distant objects up close. It comprises an optical and an ocular lens, which are usually housed in an extendable telescopic tube.

This one was made on the Rue des Portes by the Paris-based firm Gemichon. It was used by Antonio Ulloa and Jorge Juan on their expedition to South America to measure the length of a degree of latitude (1735–46), known as the Geodesic Mission to the Equator.