The Pneumatics of Hero of Alexandria

together, but rather dispersed in minute parts in the air, in water, in fire, and in other bodies. And in truth, one is forced to agree with these, for from what appears and is sensibly known, it will be clear beyond doubt that it is so, since the vessels that appear to many to be empty are not truly empty, as they believe, but are full of air. Air, furthermore (such is the opinion of those who treat natural things), is composed of bodies of this condition, so minute and light that for the most part they hide from the cognition of the senses. For if water is poured into a vessel that appears empty to us, as much water as enters into it, an equal part of air will go out in exchange. And that the matter is so can be verified thus: if one, having turned upside down the vessel that appears empty, submerges it just as it is into water, keeping it upright, water will not enter into it, even though it is completely submerged. From this it is understood that air, being a body, prevents the water from entering, since all that place which is in the vessel is already occupied by it. Now, if someone makes a hole in the bottom of the vessel, the water will then enter into it through the mouth, and the air will exit through the hole made. Furthermore, before the bottom of the vessel is pierced, if one pulls it straight out of the water and then turns it upwards, they will see its entire inner surface not to be wet, nor even touched by the water, just as it was before it was submerged. Whence it is necessary to conclude that air is a body, and when it moves, there is generated from the movement a certain spirit a breath or vital air, which is nothing other than the same moved air. Therefore, when the vessel is pierced at the bottom and water enters into it, if one brings their hand near that hole, they will feel a spirit breathing from the vessel, which is only the air driven out by the water. Therefore, one should not believe that among the things that have being there is found a kind of vacuum that by its nature stays amassed within itself, but rather one joined in brief particles in the air, in water, and in other bodies, except, however, if one were not to believe that only the Diamond is free from any kind of vacuum, as it is something that cannot be set on fire, much less broken, and when struck, it hides itself and enters back into anvils and hammers; now this