(John Matthew), a celebrated French mathematician and engineer, was born at Lyons in 1657. M. du Hamel, 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 Mortemart made use of Chazelles, to teach him mathematics; and, the year after, procured him the preferment of hydrography professor for the galleys of Marseille, where he set up a school for young pilots designed 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 shewed the practice of what he taught. In the years 1687 and 1688, he made two other sea-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 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 upon the ocean. Chazelles was sent to the west coasts in July 1689, to examine the practicability of this scheme; and in 1690, fifteen galleys new built fell from Rochefort, and cruised as far as Torbay in England, and proved serviceable at the descent upon Tenmouth. 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, *viz.* a large description of every haven, of the depth, the tides, the dangers and advantages discovered, &c. These maps were inserted in the *Neptune Françoise*, published in 1692, in which year Chazelles was engineer at the descent at Oudelle. In 1693, Monsieur de Pontchartrain, then secretary of state for the marine, and afterwards chancellor of France, resolved to get the *Neptune Françoise* carried on to a second volume, which was also to take in 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 by Greece, Egypt, and the other parts of Turkey, with his quadrant and telescope in his hand. When he was in Egypt he measured the pyramids; and finding the sides of the largest precisely facing the four cardinal points, naturally concluded this position to have been intended, and also that the poles of the earth and meridians had not since deviated. Chazelles likewise made a report of his voyage in the Levant, and gave the academy all the satisfaction they wanted concerning the position of Alexandria; upon which he was made a member of the academy in 1695. He died in 1710.