The Pneumatics of Hero of Alexandria

cold, and in consequence contrary in quality to the exhalations, which are hot and dry, it opposed them, and by contrasting, forced them back down; whence, in that conflict, a great movement of air was caused, and successively the wind. Regarding this, many things could be adduced that do not need to be mentioned in this place. But whoever desires to have complete knowledge of it should recur to the Anemologia treatise on wind of our Most Illustrious Signor Federico Bonaventura, which is just now coming to light, and there he will find the whole subject of winds most subtly examined and fully resolved with much learning. Let it suffice for us to say that spirit, according to our Hero, is properly air moved within machines and spiritual vessels by means of the contrast that some elements make one with the other.

Place is the boundary of that body which contains [it], and every place, as place, is precisely equal to the contained body. But if, insofar as it contains, one could say it is larger, it does not matter to consider how much [it relates] to our whole. Besides this, every body is necessarily in some place, and in every place it is necessary that there be some body, and the ambit and circumference of the heavens is the common place of the universe. Motion has many species, but three are considered by mechanics: namely, attraction; that which is done by pushing; and the third, which is natural, such as that of heavy things to the center and of light things to the height. The motion of attraction and of pushing, considered by the mechanic, is always with violence, even if Cardano Gerolamo Cardano, 16th-century mathematician and physician seems to hold the contrary, affirming that it comes from the proper form of the element, which abhors a rarity or density greater than what can naturally befit it.

Violent motion is stronger in the beginning and in the middle, just as natural [motion] has more force at the end. There are four causes that render violent motion fast and durable: first, that the moving cause moves quickly from the beginning; second, that it moves through a long space; third, is the disposition of the medium through which it moves, that it should have in itself such rarity that it does not impede the motion; fourth, is the figure of the thing that moves and that is moved, so that one can promptly operate and the other receive the impression. Nothing moves without a motor, and the thing moved with violence does not have the principle of