The Joô Jacinto de Magalhês Collection consists of eleven letters on optics and the manufacture of telescopes, all written by Magalhês in French. Addressed to Charles Messier (1774-1776), Baudouin de Guemadeuc, and the Abb ̆L. Garrellon of the monastery at Molesme (1783-1788), these make mention of the colleagues including William Herschel (1738-1822), and Ruggero Giuseppe Boscovich (1711-1787), and the instrument makers Peter Dollond, and John Edwards. Discussing reflecting and Newtonian telescopes, the need for quality flint glass, optics, and other topics, the collection offers insight into the manufacture and distribution of scientific instrumentation in the late 18th century.