Torricelli's first barometer, 1643.
© Science Museum / Science & Society Picture Library
Replica. The Italian mathematician, Evangelista Torricelli (1608-1647), was the first person to create a sustained vacuum and to discover the principle of the barometer. He worked as Galileo's asistant just before Galileo's death in 1641. In 1643, Torricelli experimented with vacuums to demonstrate that atmospheric presure determines the height to which a fluid will rise in a tube when inverted over the same liquid. This concept led to the development of the barometer. The barometer shown here is a replica of the four foot tube barometer that Torricelli used in this experiment.