The Pneumatics of Hero of Alexandria

of which is somewhat larger than the first tube and equally distant from it. The mouth E. F. of this one must be plugged most diligently, so that no air may enter it; but the lower mouth G. H. must be placed at such a distance from the bottom of the vessel that the water, wishing to exit, may flow freely.

A technical woodcut diagram shows a large vessel (A, B) with a lid. Inside, there is a complex system involving a smaller internal vessel and two vertical tubes. One tube (C, D, I, K) enters from the top lid into the smaller vessel. Another tube (E, F, G, H) is a siphon-like structure. The diagram is integrated into the text flow.

Once arranged as I have described, if we draw out the air that is in the tube C. D. through the mouth D., we will consequently also draw out the water that is in the vessel, which will all flow out by reason of that part of the tube that extends outside below the foot of the vessel. This is because the air that is between the water and the tube C. in I. K., being drawn through the tube E. F. by the mouth D., will pull the water with it. The flow of this water will not stop due to the portion that is outside the vessel, but if the tube E. F. G. H. does not exit, the flow of water will cease, even if the surface of the water is at C., with the excess remaining stationary. But because the air cannot enter underneath the entire tube E. F. G. H. submerged in the water, the flow will not stop, and the air having entered the vessel A. B. as the water exits, water will succeed in its place, because the mouth of the tube that is outside the vessel is always lower than the surface of the moisture that is within it.

Nor being able to make these surfaces equal due to the greater gravity of the water, it will happen that all the water will exit from the vessel. And if we do not wish to draw out the air contained in the tube C. D. & I. K. with our mouth, we will fill the vessel A. B. with water until it begins the flow through the tube C. D., and thus all the water that is in the vessel will flow out, and this tube will be called a Siphone Spiritale Spiritual Siphon.

From what has been said, it is clear that the flow of the tube (while it remains stationary) will be unequal, and the same will happen if the vessel is pierced at the bottom and the water flows out. Indeed, its flow will be unequal, because at the beginning of the effusion it is pressed by greater gravity, which always becomes less as the water in the vessel drops, causing the flow to become smaller and weaker. And the greater the excess of the tube, the faster the flow becomes, and the slower it is when it is less, as was also said in the previous proposition. It is therefore manifest from what we have said that the flow of water through a pipe or cane is always unequal; hence, proceeding further, it is necessary to demonstrate the always-equal flow of water through the bent pipe proposed above.

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OF THE ALWAYS EQUAL FLOW THROUGH THE BENT TUBE. Theor. III.

Let there be a vessel A. B. filled with water up to the surface H. K., in which floats a small basin C. D. The mouth of this basin must be plugged very well with its lid C. D. at the bottom of the basin; a hole must be made through which one leg of the bent tube E. F. G. passes, as in the following example.

A technical woodcut diagram shows a tall vessel (A, B) filled with liquid up to the level H-K. Inside floats a smaller lidded vessel (C, D) from which a bent siphon tube (E, F, G) emerges, passing through the side of the larger vessel to discharge liquid below the current level.

These holes must be excellently sealed with tin around the tube, assuming we make the vessel of copper or similar metal. The other leg of the tube should be placed outside the vessel, with its mouth lower than the surface of the water in the vessel, as above. If we draw the air with our mouth through the mouth of the tube that is outside the vessel, the water will follow in the same way, because there cannot be a place in the tube that is completely void. It will take the flow as a principle and will run until all the water in the vessel has flowed out, and this flow will be equal. This is because as the surface of the water drops, the basin will also drop with the tube fixed into it, and the greater the external excess, the faster the flow of water will be, even if it is always equal in itself.

OF THE FLOW THROUGH THE BENT PIPE, PARTLY EQUAL AND PARTLY UNEQUAL. Theor. IIII.

The flow will sometimes be equal and sometimes unequal, similarly done through the bent pipe according to our will, and at other times, if we wish, equal in itself, or faster or slower than the first flow. Let there be, for example, the vessel full of water A. B. and the basin C. D., covered as said above, through the middle of which—both the bottom and the lid—a tube is inserted, wider than the interior leg of the bent pipe. In the example below, this is E. F., sealed very well around the hole in the bottom and lid of the basin with tin, assuming, as said above, that the vessel is of copper. On each side of the vessel, two tracks shall be placed, on the inner side of which a channel is hollowed out, and at the top of these, another track is placed, fastening this one and the others in the vessel. The two tracks with the channels hollowed into them will be G. H. I. K.