JOHN THEOPHILUS, who introduced the practice of reading public lectures in experimental philosophy, in the metropolis, and who made several improvements in mechanics; was the son of the reverend John Desaguliers, a French Protestant refugee, and was born at Rochelle in 1683. His father brought him to England an infant; and at a proper age placed him at Christ-Church College, Oxford; where he succeeded Dr Keil in reading lectures on experimental philosophy at Hart-Hall. The magnificent duke of Chandos made Dr Desaguliers his chaplain, and presented him to the living of Edgeware, near his seat at Cannons: and he was afterwards chaplain to Frederic prince of Wales. He read lectures with great success to the time of his death in 1749. He communicated many curious papers printed in the Philosophical Transactions; published a valuable Course of Experimental Philosophy, in 2 vols 4to; and gave an edition of Gregory's Elements of Catoptries and Dioptries, with an Appendix on reflecting telescopes, 8vo. He was a member of the Royal Society, and of several foreign academies.