Syringes, Siphons and Suckling Infants

Abstract

Thus far, Pascal has been dealing with fluids such as water and mercury. But what about air—does it have weight? According to Aristotle, gravity is a quality possessed by the elements earth and water; it causes them to fall toward the center of the world. Levity, on the other hand, is a quality which is possessed by the elements fire and air; it causes them to rise towards the heavens. Gravity and levity are thus opposing and absolute qualities of substances. Aware of Aristotle’s theory, Pascal begins his Treatise on the Weight of the Mass of the Air by reminding the reader of the experimental evidence which proves that air in fact possesses gravity, or heaviness, just like rocks. He then proceeds to derive the consequences of this fact. In particular, he suggests that many of the phenomena which had previously been attributed to nature’s apparent abhorrence of a vacuum—a doctrine advanced by Aristotle and maintained by Galileo—could be understood more readily by considering Earth’s atmosphere to be a vast sea of air whose weight presses down upon bodies submerged in it.

It is just as natural for air to enter and drop down into the lungs when they open, as for wine to drop into a bottle when it is poured in.

—Blaise Pascal