The Pneumatics of Hero of Alexandria

ON PNEUMATICS.

...providing. For indeed, if one pours water into a vessel that appears to be empty, as much water as enters the vessel, just as much air will depart from it. Anyone can understand what has been said from the following: for if someone takes a vessel that appears empty, turns it upside down, and presses it down into water—keeping it perfectly upright—the water will not enter it, even if the vessel is entirely submerged. Therefore, it is clear that air, since it is a body corpus In ancient physics, a "body" is anything that occupies space and offers resistance, as opposed to a void., does not permit the water to enter because the entire space within the vessel is already filled with it.

If, however, one should pierce the bottom of the vessel, the water will then enter into it through the mouth, but the air will exit through the hole. Furthermore, if before the bottom is pierced, one lifts the upright vessel out of the water and turns it over, they will see that its entire interior surface is free from moisture and pure, exactly as it was before it was submerged. For this reason, we must consider air to be a body.

Now, wind spiritus original: "spiritus." While this often means "spirit" or "breath," in Hero's mechanics it specifically refers to air in motion, which we would call a draft or wind. is produced when it is moved; for wind is nothing other than air in motion. Thus, when the vessel is pierced at the bottom and the water enters, if one places a hand over the hole, they will feel