As a schoolboy I had a friend called David Appleby, whom the Christian Brothers imaginatively labelled Daithi Mac an Uill. I suppose, by the same reasoning, had Evangelista Torricelli been dispatched to school in Ireland, he would have become Soiscealai Tuar Ui Cheallaigh.
But as it happened, Torricelli was educated, not by the Christian Brothers, but by Jesuits, and spent all his life in Italy. He was born in Faenze 389 years ago, on October 15th, 1608. Among other things, Torricelli was a meteorologist and, not unusually for members of that singular profession, he was noted in his lifetime as a man of great personal modesty and charm.
But he was also one of the most brilliant thinkers of his day, and his place in history was assured by what is now called the Torricellian Experiment, performed in 1643.
It was essentially the invention of the mercury barometer. Although the air around us is a most familiar substance, it took the philosophers of old a long time to come to grips with its essential properties.
Aristotle, for example, was one of the first to suspect that it might have weight. To prove his suspicion, he took a leather bag and weighed it when it was "empty" of air, that is, pressed flat. Next he weighed the bag when it was full of air. To his great disappointment he found there was no difference, and reasonably concluded that the air was weightless.
This was the accepted view for 2,000 years until Torricelli came along. At the time he was court mathematician to the Grand Duke Ferdinand of Tuscany, and the prototype for the experiment of which he is the eponym consisted of a glass bulb fitted with a neck some 40 inches long.
The tube was filled with mercury and inverted into a dish containing more mercury. Torricelli found that in such circumstances the mercury in the glass tube would fall to a certain level, about 30 inches above the surface of the mercury in the dish, but no further. Moreover, the length of the column rose and fell with changes in the weather.
Since the space above the mercury in the tube and that in the glass bulb was a vacuum, the only force acting on the liquid was the "weight" of the air outside, pressing down on the fluid in the dish.
Aristotle's suspicions were finally vindicated, and even to this day the space above the mercury in a barometer, empty except for a small quantity of mercury vapour, is known as the Torricellian vacuum.