Horace Bénédict de Saussure (17.02.1740 - 22.01.1799) was a Swiss physicist and geographer. He was born in Conches, near Geneva. In 1762—86 he was professor at the Academy of Geneva.
His physical research concerned heat, electricity and optics. In 1783 he invented the hair hygrometer. He established (1784) that the rate of evaporation from a water surface depends on the humidity of the surrounding air. He studied the thermal expansion of air and atmospheric electricity. He determined the coefficient of thermal expansion of air (1/235 deg).
He travelled widely for geological and meteorological purposes. He made (1787) an ascent of Mont Blanc and determined its height with a barometer (4833 m). He studied the change of air pressure and temperature with height, in particular finding that in the mountains the air temperature falls by 0.64 deg for every 100 m. He carried out experiments on atmospheric electricity and studied optical phenomena in the atmosphere and the structure of clouds.