The Pneumatics of Hero of Alexandria

substances that decompose in bodies pass through smoke into fiery, aerial, and earthly substances. Indeed, the most subtle parts are carried, as they are lighter, to the upper place, where fire is above the air and below the circle of the Moon. Those that are somewhat coarser remain in the air, and the heaviest, together with those that rise for a while but cannot remain there due to their continuous gravity, descend again into the lower part and are added to the earth. And water itself, corrupted by fire, is changed into air; for the vapors that rise from boiling vessels are nothing other than subtleties of moisture that pass into the air. Thus, it is manifest that fire dissolves and transmutes everything coarser than itself, and that through the exhalations that rise from the earth, coarser bodies are transmuted into more subtle substances. In no other way do dews rise on high, unless the water that is in the earth is attenuated by its exhalation. And this exhalation is produced by a certain hot substance of the sun, which is in the bowels of the earth and warms that place. And this is all the more so if it is sulfurous or bituminous, which, when heated, for the most part generates exhalation. And the waters found in the earth become hot for the same reasons. The most subtle part of the dew is therefore transmuted into air, and the coarser part, forced by the strength of the exhalation, rises somewhat on high, and through the cooling conversion of the Sun, falls back down onto the earth. But winds are born from the vehement exhalation of air, thinned and driven by its continuous motion. The motion of the air is not equally fast, but is much faster at the beginning near the exhalation and always becomes slower and weaker the further it moves from the place whence it moves. This also happens in heavy things that are carried upwards: their motion is much faster near the place where the violence that drives them exists, and slower in the upper part, because the driving force does not accompany them with the same strength as at the beginning of their movement. For this reason, they return again to their natural place, from which they departed, that is, into the lower parts. If they were always accompanied by the same driving force with equal speed, they would certainly never cease. But by ceasing little by little, the velocity of the moved thing is also seen to cease. And water also is transmuted into earthly substance when we pour water into a concave place dug in the earth, which, shortly after being imbibed by the earthly substance, vanishes and, mixing with it, becomes earth. But if there is someone who says that it is constrained and does not come from being drunk by the earth, but evaporates and dries up, either by the heat of the Sun or otherwise, that person will truly see himself in error. For the same water poured into a vessel of glass, or copper, or other dense material, and exposed to the Sun for a great space of time, will not diminish except for a small part. Thus it is seen that water is transmuted into earthly substance, and that the viscosity, so to speak, or the mucilage of the earth, is the transmutation of water into earthly substance. The subtle is also changed into a coarser substance, as we see in extinguished lamps where the oil is lacking, the flame being carried somewhat upwards, and as if driven to depart from its own place and head to its supreme place which is above the air, but being overcome by the many intermixtures of the air, it is not carried to the intended place, but...

mixed and complicated by aerial bodies, it is converted into air. And the same must be understood of air itself: for if we immerse the vessel in water, closed in some not-very-large container, and then uncover it so that the water enters into it through the mouth above, the air certainly will depart from outside the vessel, or, overcome by the great quantity of water, it will again mix and complicate itself in such a way that it will become water. In the same way, air corrupted in cucurbitule distilling vessels or cupping glasses, and thinned by fire, exits due to the rarity of the vessel, and the body being made void, it draws the surrounding matter to itself, be it of whatever quality one wishes. But when the cucurbit breathes, with air succeeding into the evacuated place, it will no longer pull the matter. And if generally someone were to say that nothing at all is empty, many arguments could be found to demonstrate this, and perhaps to persuade it with words, since they bring forward no sensible demonstration. But in those things that appear clear and fall under the sense, they will certainly demonstrate the Void as gathered together and made outside of its Nature, and being disseminated in small parts, and that these bodies fill the disseminated Voids through compression. To those who labor to bring forward probable reasons for this, one should certainly not lend an ear. For, having fabricated a Sphere, the thickness of which is of metal plate so that it cannot be easily broken, but well-made and excellently sealed all around, then having perforated it and placed a copper tube in the hole—such that the place perforated opposite, according to the Diameter, does not close the hole opposite it, so that the water may flow, and making the other part of the tube extend about three fingers out of the sphere—and sealing with tin the circumference of the hole through which the tube is inserted, if we then close that tube and the external surface of the Sphere so that, wishing to inflate it with the mouth, the spirito spirit/breath could by no means exit: we will see that what is contained in it is certainly nothing other than the Air existing in it in the same way as happens in those other vessels which are called empty, which, all filled and applied in a certain continuity to their circumference, not being able to have any sort of void in them, cannot have water or other air imposed upon them. It will not depart from what was inside before; rather, it will happen that by making violence to force it in, the vessel will break before it can receive any, because it is full, and the bodies of air cannot contract into a smaller size, because it would be necessary that certain intervals be made between them, in which the compressed bodies would be of smaller mass. This is not possible, as there is no void at all. And when, according to all the surfaces, the bodies apply themselves together, similarly, in the circumference of the Vessel, they cannot give place to other bodies, there being no void at all. And for this reason, by no means in the proposed Sphere can any of those bodies that are outside it be put, if first some part of the Air previously contained in it does not depart. That is, if all the place is congested and continuous, as one thinks. But if someone comes to inflate the Sphere through the mouth of the tube, he will certainly introduce much spirito spirit/breath, though the Air that is in it will not depart; which, as it always is, is manifestly demonstrated that in the Sphere it comes to be made...