Evangelista Torricelli and the mercury barometer

Evangelista Torricelli – A Hero of Vacuum

Born in 1608 in Italy during the Renaissance, Torricelli was to make significant contributions in mathematics and physics. He studied mathematics in Pisa from 1624 and in 1632 wrote to the prominent Galileo in support of his Copernican view. 

Torricelli’s work was largely unknown between 1632 and 1641, when Galileo was documented to have received a treatise by Torricelli on the path of projectiles. In October 1641 Torricelli was to accept Galileo’s invitation to visit and work with him. However, this lasted only a few months before Galileo’s death in January 1642. Torricelli was then to succeed him as Professor at the University of Pisa. 

It is chronicled that between 1640 and 1643 Gaspero Berti was involved in empirical tests in Italy of the level of ascent of water within a siphon. This had been estimated by Galileo to be 18 braccia; approximately 11 metres. At issue was that the experiment was at the time not universally convincing as to providing a vacuum. The first mercury filled glass tube was generally accepted to have been invented in 1643 by Torricelli, which became known as Torricelli’s mercury barometer. In this he produced a vacuum by filling a glass tube with mercury, inverting it and then submerging the open end in a vessel of mercury. This was to be effectively the first barometer (with a height of ~760mm of Mercury, 760 mmHg) and is a configuration still in use for absolute pressure measurements today.

 Further work of Torricelli included his writings on Rectilinear motion, geometry and trajectories as well as ‘Torricelli’s law’ for the speed of a fluid flowing out of an opening (a forerunner of Bernoulli’s Law). He also recognised that wind is caused by two regions of air being at different temperature and density. 

Torricelli died in Florence in 1647 and the unit of pressure 1mmHg was named as 1 Torr, in his honour. 