JEAN MATHIEU, a celebrated French mathematician and engineer, was born at Lyons in 1657. M. Duhamel, with whom he got acquainted, finding his genius incline towards astronomy, presented him to M. Cassini, who employed him in his observatory. In 1684 the Duke of Mortemar made use of Chazelles to teach him mathematics, and, the year after, procured him the preferment of hydrographic professor for the galleys of Marseilles, where he set up a school for young pilots designing to serve aboard the galleys. In 1686, the galleys made four little campaigns, or rather four courses, purely for exercise. Chazelles went on board every time with them, kept his school upon the sea, and showed the practice of what he taught. In the years 1687 and 1688 he made two other naval campaigns, in which he drew a great many plans of ports, roads, towns, and forts, which were lodged with the ministers of state. At the beginning of the war which ended with the peace of Ryswick, some marine officers, and Chazelles among the rest, fancied that the galleys might be so contrived as to live upon the ocean; that they might serve to tow the men of war when the wind failed or proved contrary, and also help to secure the coast of France. Chazelles was sent to the west coasts in July 1689 to examine the practicability of this scheme; and in 1690 fifteen galleys, newly built, set sail from Rochefort, and cruised as far as Torbay, in England, and proved serviceable at the descent upon Tinmouth. After this he digested into order the observations he had made on the coasts of the ocean, and drew distinct maps, with a portolan to them, namely, a large description of every haven, of the depth, the tides, the dangers and advantages discovered, and so forth. These maps were inserted in the Neptune Francais, published in 1692, in which year Chazelles acted as engineer at the descent at Oneille. In 1693, Monsieur de Pontchartrain, then secretary of state for the marine, and afterwards chancellor of France, resolved to get the Neptune Francais carried on to a second volume, which was to include the hydrography of the Mediterranean. Chazelles desired that he might have a year's voyage on this sea for making astronomical observations; and the request being granted, he passed through Greece, Egypt, and other parts of Turkey, with his quadrant and telescope in his hand. When he was in Egypt, he measured the pyramids; and finding that the angles formed by the sides of the largest were in the precise 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 gave the academy all the satisfaction they desired concerning the position of Alexandria; upon which he was made a member of the academy in 1695. He died in 1710.