βάρος + μέτρον

Ancient Greek βάρος (báros) meant weight or heaviness, and μέτρον (métron) meant measure. The compound barometer—weight measurer—was coined in 1665 by Robert Boyle to describe the instrument Evangelista Torricelli had invented twenty-two years earlier. Torricelli, a student of Galileo, filled a glass tube with mercury, inverted it in a dish, and watched the mercury column drop to about 760 millimeters. The weight of the atmosphere, pressing on the mercury in the dish, supported the column. Air had weight, and now it could be measured.

The barometer transformed weather prediction from folklore to science. Before Torricelli, weather forecasting relied on cloud observation, wind direction, animal behavior, and proverbs. After Torricelli, a falling mercury column meant a storm was approaching. By the late 1600s, barometers hung in the homes of educated Europeans alongside their clocks and thermometers.

The word barometric expanded into metaphor by the nineteenth century. A barometric reading of public opinion, a barometric measure of economic confidence. The image was of pressure—invisible, measurable, significant. Just as atmospheric pressure determines weather, social and economic pressures determine events.

Modern barometers use electronic pressure sensors rather than mercury, but the word persists. Smartphone weather apps display barometric pressure to millions of users who have never seen a mercury column. The Greek compound that Robert Boyle assembled in 1665 names a concept that remains as relevant as it was when Torricelli first watched his mercury drop.