The Ingenious and Curious Pneumatic Motions of Hero

...is in the stone, they do not enter into its body, but stop on the exterior surface: hence it happens that since they do not penetrate within, they do not induce heat calidità heat/warmth there, as happens in other bodies. But the bodies of air have among themselves a certain coherence, though not in every part; rather, it is through certain interspersed intervals, which we shall call vacuums, like the sand that is on the shores. This makes one understand in the mind that the small particles of sand are similar to aerial bodies, and that the air interspersed between the particles of sand is similar to the vacuums contained within the air; the latter, when forced by violent power, must (entering into the empty spaces) condense. Those bodies are forced and compressed, and their nature is violated; when the force that constrained it is released and relaxed, it must return again to its order due to the natural contention that exists between natural bodies; as happens in the shavings of horns and in dry sponges, which, if compressed, return to their previous place when released, taking on the same size again. The same happens if the small particles in the air are pulled apart by violent force, and because of this the vacuum becomes larger than its nature allows; they return again into themselves. For due to the sudden evacuation, the bodies must return again into themselves and to their own state, notwithstanding whatever might oppose them. This is seen if one takes a very light vessel and, through its narrow mouth, draws out the breath or air that is inside with one's mouth; then, immediately released, the said vessel will hang from the lips of that person, and the vacuum will attract the flesh, constrained by its nature, until the empty space is filled. This very clearly demonstrates to us that the space within the body of the vessel had been totally a vacuum. But this is also manifest from this other reason. Those vessels that are called ventosi medici medical cupping glasses, which are made of glass with a very small mouth, when one wants to fill them with water, one sucks through the mouth; immediately after removing the air, they submerge them in water, in which, removed from the mouth, the said vessel is pulled upward by the vacuum. Thus, one sees the empty place being filled, and the water, forced by the power of the vacuum, is carried upward against its nature. And that which is clear from all this is certainly not alien to what we have discussed above, since it is very certain that when the body is removed, not only does the manifest gravity not relax, but the underlying matter is drawn in by the rarity of the body due to the same cause. But when fire is placed in them, it corrupts and thins the air contained within them, no less than other bodies are corrupted by them and transmuted into more subtle substances, I say: air, water, and earth. And that they are corrupted by it is manifest from burnt coals, which keep the same size they had before combustion, or are only slightly smaller, yet are of much less weight. And those substances that are corrupted in bodies pass through smoke into igneous, aerial, and earthly substance; for the more subtle parts are carried, as lighter, into the upper place, where fire is above the air and below the circle of the Moon, and those that are a little coarser are in the air. The heavier ones, along with those, rise for a while, but being unable to form themselves in it due to its continuous gravity, they descend again into the lower part and join the earth. Water, also, when corrupted by fire, is changed into air; for the vapors that rise from boiling vessels are nothing other than the thinning of moisture.