1-158-620 - Oxford Science Archive/Heritage Images

Evangelista Torricelli's demonstration of the effect of atmospheric pressure on a column of liquid, 1643 (1873). Torricelli (1608-1647), Italian physicist and mathematician, showed that the height of a column of liquid is governed by atmospheric pressure and that the height of the column is directly proportional to the density of the liquid. Water will rise to 9.75m (32 feet) but mercury, which is approximately 13.5 times denser, will only rise to .736m (29 ins). A metre (3 feet) tube is filled with mercury and the open end placed in a dish of mercury. The liquid will fall in the tube until the weight of the column is in equilibrium with atmospheric pressure. From The Atmosphere by Camille Flammarion. (London, 1873).