A French scientist who was born in poverty and rose to become an outstanding chemist and physicist. He discovered carbon tetrachloride and measured the chemical composition of the atmosphere around the world. He made a series (p. 323) of measurement of the specific heats of many solids, liquids, and gases, of the expansion of gases, and of vapour pressures. He developed the use of an accurate air thermometer. He also designed an efficient hygrometer for measuring dew point and invented an apparatus for measuring the coefficient of expansion of mercury.