V
GALILEO AND THE NEW PHYSICS
A History of Science: in Five Volumes. Volume II: The Beginnings of Modern Science | ||
TORRICELLI
In the closing years of his life Galileo took into his family, as his adopted disciple in science, a young man, Evangelista Torricelli (1608-1647), who proved himself, during his short lifetime, to be a worthy follower of his great master. Not only worthy on account of his great scientific discoveries, but grateful as well, for when he had made the great discovery that the "suction'' made by a vacuum was really nothing but air pressure, and not suction at all, he regretted that so important a step in science might not have been made by his great teacher, Galileo, instead of by himself. "This generosity of Torricelli,'' says Playfair, "was, perhaps, rarer than his genius: there are more who might have discovered the suspension of mercury in the barometer than who would have been willing to part with the honor of the discovery to a master or a friend.''
Torricelli's discovery was made in 1643, less than two years after the death of his master. Galileo had observed that water will not rise in an exhausted tube, such as a pump, to a height greater than thirty-three feet, but he was never able to offer a satisfactory
It had long been suspected and believed that the density of the atmosphere varies at certain times. That the air is sometimes "heavy'' and at other times "light'' is apparent to the senses without scientific apparatus for demonstration. It is evident, then, that Torricelli's column of mercury should rise and fall just in proportion to the lightness or heaviness of the air. A short series of observations proved that it did so, and with those observations went naturally the observations as to changes in the weather. It was only necessary, therefore, to scratch a scale on the glass tube, indicating relative atmospheric pressures, and the Torricellian barometer was complete.
Such a revolutionary theory and such an important discovery were, of course, not to be accepted without controversy, but the feeble arguments of the opponents showed how untenable the old theory had become. In 1648 Pascal suggested that if the theory of the pressure of air upon the mercury was correct, it could be demonstrated by ascending a mountain with the mercury tube. As the air was known to get progressively lighter from base to summit, the height of the column should be progressively lessened as the ascent was made, and increase again on the descent into the denser air. The experiment was made on the mountain called the Puy-de-Dôme, in Auvergne, and the column of mercury fell and rose progressively through a space of about three inches as the ascent and descent were made.
This experiment practically sealed the verdict on the new theory, but it also suggested something more. If the mercury descended to a certain mark on the
BLAISE PASCAL
(From the painting by Philippe de Champagne.)
[Description: Portrait of Balise Pascal, from the painting by
Philippe de Champagne.
]
In hydraulics, also, Torricelli seems to have taken one of the first steps. He did this by showing that the water which issues from a hole in the side or bottom of a vessel does so at the same velocity as that which a body would acquire by falling from the level of the surface of the water to that of the orifice. This discovery was of the greatest importance to a correct understanding of the science of the motions of fluids. He also discovered the valuable mechanical principle that if any number of bodies be connected so that by their motion there is neither ascent nor descent of their centre of gravity, these bodies are in equilibrium.
Besides making these discoveries, he greatly improved the microscope and the telescope, and invented a simple microscope made of a globule of glass. In 1644 he published a tract on the properties of the cycloid in which he suggested a solution of the problem of its quadrature. As soon as this pamphlet appeared its author was accused by Gilles Roberval (1602-1675) of having appropriated a solution already offered by him. This led to a long debate, during which Torricelli was seized with a fever, from the effects of which he died, in Florence, October 25, 1647. There is reason to believe, however, that while Roberval's discovery was made before Torricelli's, the latter reached his conclusions independently.
V
GALILEO AND THE NEW PHYSICS
A History of Science: in Five Volumes. Volume II: The Beginnings of Modern Science | ||