JEAN MATHIEU DE, a French mathematician and engineer, was born at Lyons in 1657. He was employed for some time by M. Cassini in measuring the meridian, and afterwards taught mathematics to the Duke of Mortemart, who procured him the preferment of hydrographic professor for the galleys of Marseilles. In 1696 Chazelles went on board the galleys in their campaigns, and kept his school at sea. He was sent to the west coasts in July 1689 to examine the practicability of so contriving galleys that they might live upon the ocean, and be employed to tug the men-of-war when becalmed; and having set sail with fifteen galleys from Rochefort, cruised as far as Torbay, in England, and proved serviceable at the descent upon Tyne-mouth. On his return he published his observations, and drew maps of the coasts he had visited, with a description of all the harbours, &c., discovered. These maps were inserted in the Neptune Francais, published in 1692, in which year Chazelles acted as engineer at the descent on Oneille. In 1693, Monsieur de Pontchartrain, secretary of state for the marine, engaged Chazelles to publish a second volume of the Neptune Francais, which was to include the hydrography of the Mediterranean. For this purpose he passed through Greece, Egypt, and other parts of Turkey. When in Egypt he measured the pyramids; and finding that the angles formed by the sides of the largest were in the direction of the four cardinal points, he concluded that this position must have been intended, and also that the poles of the earth and meridians had not deviated since the erection of these colossal structures. Chazelles likewise made a report of his voyage in the Levant, and concerning the position of Alexandria. He was made a member of the academy in 1695, and died in 1710.