Heronis Alexandrini spiritalium liber

the spirit original: "spiritum" exiting from the vessel. This, however, is nothing other than air expelled by the water. Therefore, it is not to be thought that in these things which exist, a certain nature of a vacuum concentrated by itself exists, but that it is disseminated in small parts in the air, in moisture, and in other bodies, unless perhaps someone believes that only the diamond is free from the nature of the vacuum: for it can neither be ignited, nor broken; and when struck upon anvils and hammers, it enters entirely. This, however, happens to it, not because it lacks a vacuum, but because of its continuous density. For the corpuscles of fire, since they are thicker than the vacuum that is in the stone, do not enter it at all, but only touch the outer surface. Therefore, since they do not penetrate inside, they do not induce heat in it as they do in other bodies. But the bodies of air indeed cohere among themselves, not however on every side, but they have certain empty intervals interposed, just like the sand that is on the shores. Therefore, it should be conceived in the mind that the particles of sand are similar to the bodies of air, and the air which is between...