Institute and Museum of History of Science, Florence, ITALY
The possibility of the
existence of the vacuum was firmly denied by Aristotle
in his Physics, which held sway, almost uncontended until the
mid seventeenth century. Aristotle's plenist physics gave rise to
the development and general acceptance, in the Middle Ages, of the
theory of nature's abhorrence of the void. The theory of repugnance
to the void, which would make nature prevent the production of a void
at any cost, was used to explain various phenomena, such as the workings
of the pump and the syphon: the upwards movement of water in this
device was in fact interpreted as an action performed by nature to
prevent a void after suction.
The definitive challenge to the theory of horror vacui - which had already been discussed, without conclusive results, by many authors - is one of the great merits of a disciple of Galileo, Evangelista Torricelli. In a very famous, and extraordinarily simple experiment, performed in Florence in the Spring of 1644, Torricelli showed not only that nature did not 'abhor the void', but also that it was all too simple to bring it into being.