Highly-renowned German mathematician and philosopher (1646-1716). Incredibly rare unsigned hand-addressed envelope by Gottfried Wilhelm Leibniz, 4 x 2.5, made out in French to his friend, the political philosopher Thomas Burnet de Kemney, in London, with a few autograph lines describing how to find his address. Reverse retains Leibniz's black wax seal impressed with his coat of arms. In very good to fine condition. Burnet was a conspicuous member of the brilliant Court circle at Hanover, known as a confidante of the Electress Sophia. He maintained lengthy correspondences with several luminaries of the era, including Leibniz and John Locke. A significant specimen of Leibniz's scarce handwriting, with an important association.