It had been found by the engineers engaged in the construction of fountains for Cosmo dei Medici in Florence that they could not raise water in an ordinary pump more than thirty-two feet above the reservoir. The water, having reached this height, would rise no higher. Galileo was appealed to for a solution of the difficulty. {29b} Imbued with the ancient notion that Nature abhors a vacuum, and that this was, as then prevalently believed, the explanation of the water following the elevation of the piston in the pump, the philosopher replied in effect that there were limits to the action of this principle, and that Nature’s abhorrence of a vacuum did not extend beyond thirty-two feet. He was himself, it need hardly be said, dissatisfied with such a reply, and accordingly he invited his pupil, Torricelli, to investigate the subject. The latter very soon found that the weight of the water was concerned in the result. He made experiments with a heavier fluid—mercury—and ascertained that a column of mercury enclosed in a tube three feet in length hermetically sealed at the lower end, and closed with the finger at the top, on being inserted in a basin of the same liquid and the finger withdrawn, stood at a height of about 28 inches in the basin. As the specific gravities of water and mercury were in the ratio of 32 feet and 28 inches, he was led to the conclusion that the water in the pump and the mercury in the tube at these respective heights exerted the same pressure on the same base, and that both were of course counterbalanced by a determinate force. But what was this force? He had learned from Galileo that the air was a heavy fluid, and he was carried, therefore, directly to the further conclusion that the weight of the atmosphere was the counteracting cause in both cases; in the one, pressing upon the reservoir from which the water was drawn—and in the other, on the surrounding mercury in the basin. He published his experiments and researches in 1645, but dying soon afterwards, his conclusions remained unverified.