The Pneumatics of Hero of Alexandria

reason: but if we make the hole at E., the water will flow out until the water in the vessel has dropped, so that its surface is level with the mouth of the pipe C. And if we wish to draw out all the water of the vessel, we will lower the mouth C. to the bottom of the vessel, but keeping it far enough from it that it may suffice for the flowing of the water. Some say the reason why the pierced and bent pipe has this effect is because the quantity of water in the longer leg has the force to attract, and in effect pulls the shorter one; but how false this cause is, and in what error whoever believes this is, is denied by this. Let a pipe be made such that the interior leg is long and thin, and the exterior one is much shorter, but wider, so that it may hold a greater quantity of water than the long leg, and let it be filled with water. Then, having placed the wider one in a vessel of water, or in some well (which will be the same), if we make the exterior leg flow—since it has in itself a greater abundance of water than the interior one—it will also have the force to attract the water of the greater one, and with it, it will also pull that which is in the well, and when it begins to flow, it will extract it all, or it will always flow; because the copy of exterior water is greater than that which is in the interior leg. But because it does not appear whence this derives, as truth; therefore we do not approve the aforementioned cause. But let us see the natural cause of this, saying that every continuous and still moisture takes a spherical surface whose center is the same as that of the earth; but not remaining still, it flows until it reduces itself to a spherical surface, as has been said above. Let us take two vessels, and in each of them let water be placed; let us also fill the pipe with water and with our fingers stop its mouths, placing one end in one of the aforesaid vessels so that it is submerged in the water, and similarly let us put the other leg in the other, and all the water will be made continuous; for the water that is in both vessels comes to be joined with that which is in the pipe in such a way that it is all continuous. If, therefore, the said waters, which were first in the vessels, are on one and the same surface, having been made continuous by the bent pipe submerged in them, they will remain quiet and stand still; but if of them one is lower than the other, because the water is made continuous, it is necessary also by this continuity that the higher one flows into the lower one until either all the water that is in the aforesaid vessels is reduced to one and the same surface, or until one of the said vessels is empty. But if they equalize on one and the same surface, the waters that are in these vessels will stop, one and the other; so that also the water that is in the pipe will remain still, in such a way that given that one leg and the other of it is equally submerged in each of the said surfaces (provided that they are equal), the water that is in it will remain still. If this pipe is suspended, therefore, so that it leans neither here nor there, it is again necessary that the water stops, whether it has equal width, or one leg is much greater than the other (which in this is not the cause why the water remains still or flows), but it derives from the mouths of it being equal in the water. Now let us say: why (the pipe being suspended) does the water not flow by its gravity, being lighter, having the air as a subject or "base/medium"? It is for no other reason, certainly, than because the place of the whole cannot be a

vacuum: because, if the water must exit from it, it is necessary that the upper part of the pipe first fills, into which air cannot enter by any means. Whence, if we pierce it in the upper part, the water will immediately exit from it, and in its place the air will succeed; but before said hole is made, the moisture, that is, the water that is in the pipe, strikes against the Air subject, which, not having a place where it can flow, does not let the water exit. But when by way of the hole it obtains space, then it gives space to the water and lets it flow out, filling its place, and for this reason, contrary to nature, one draws wine with the mouth through the pipe; because by pulling the air that is in the pipe it comes to be filled much more, and by being joined to that air, we come to detach it. And this is done until, with the surface of the wine, as was said above, the evacuation is made, which then the detached wine, flowing, falls into the evacuated place of the Tube, having no other place where it is permitted to flow, and for this reason, contrary to nature, it is carried upward. Otherwise, the water will be quiet in the pipe when it is established on a spherical surface, the center of which is the same as the center of the earth. For if there is any aqueous surface that has the same center as the earth, it stays quiet; but if it is possible that it does not quiet, it is necessary that, while moving, it rests. Let it quiet, therefore, that the center of its spherical surface, being the same as that of the earth, will follow the first surface. For the water, flowing here and there through one and many places, will have occupied diverse places; let it be, therefore, that each of those surfaces which have their center with the earth be intersected by some plane, and from them be created lines in said surfaces, which are circles of the circumferences which have the same center as the earth, that is A.B.C.F.G.D., and let B.G. be drawn, which because it will be equal to each of them, that is G.F.G.A., which cannot be, it is therefore forced that it quiets, and so much for this.

A circular geometric diagram showing points A, B, C, D, F, and G. G is the center of the circle. A is on the right circumference, F on the left. B is at the top. C and D are points on a horizontal line to the left of G. The diagram illustrates a spherical water surface in equilibrium relative to the Earth's center.

There is another sort of pipe or Tube, which is called the Spiritual middle, the reason for which is the same as the past one of the bent pipe. Let the vessel A.B. be full of water, in the middle of which let the tube C.D. be placed, which passing under the foot of said vessel advances; but in the upper part its mouth does not reach the mouth of the vessel A.B., but is surrounded by another Tube, the void