The Pneumatics of Hero of Alexandria

happens well, not because it lacks a vacuum, but because of its excessive continuous density, for since the little bodies of fire are larger than the particles of the vacuum contained in the stone, they do not have the power to penetrate it, but only circle the exterior surface; hence, not entering inside, they do not induce heat in it as in other bodies. But the bodies of air, although they are restricted together, are not therefore absolutely continuous; rather, they have certain vacuum spaces interspersed among them, like the sand that lies upon the shores, for one must imagine that the particles of sand are similar to the bodies of air, and the air that is placed between the particles of sand is similar to those vacuums sown through the air. From this it proceeds that, by the work of some force, the air restricts itself together and comes to occupy the places of the vacuums when its bodies are violently pressed and restricted one with the other, but then, that force ceasing, they return again to keep the order of before, moved by their own natural withdrawal, as is expressly seen in shavings of horn and in dry sponges, which, if they are pressed and then released, return into the same former space and take back their original size. Similarly, if the particles of air are separated from one another with some violence, such that a larger vacuum follows than nature allows, they go to meet again until the bodies are reunited together. And the movement that occurs through the vacuum space is rapid, because it has no contrary repulsion. If someone, therefore, taking a very light vessel that has a narrow mouth, places it to their mouth and sucks out the air, even if the vessel is not held, it will remain attached to the lips by itself, the vacuum pulling the flesh to fill the place made more vacuum; and in this way, it is found that the particles of the vacuum that were in the vessel have united together. But this is manifested also with another proof, for the glass eggs original: "uoua di vetro" for holding fragrant liquids, which have a narrow mouth, when one wants to fill them, by sucking with the mouth the air that was enclosed inside them and then covering that hole with a finger, are turned upside down into water, and then, upon removing the finger, the water comes