Fig. 60.
Figs. 60, 61, 62 are syphons described by Hero of Alexandria who lived 120 B. C.; the descriptions of the figures are the translation of the original.
Let A B C D (Fig. 60) be a vessel open at the top, and through its bottom pass a tube, either an inclosed pipe as E F G, or a bent syphon G H K. When the vessel A B C D is filled, and the water runs over, a discharge will begin and continue till the vessel is empty, if the interior opening is so near the bottom of the vessel as only to leave a passage for the water.
As before, let there be a vessel, A B (Fig. 61), containing water. Through its bottom insert a tube, C D, soldered into the bottom and projecting below. Let the aperture C of the syphon approach to the mouth of the vessel A B, and let another tube, E F, inclose the tube C D, the distance between the tubes being everywhere equal, and the mouth of the outer tube being closed by a plate, E G, a little above the mouth C. If we exhaust, by suction through the mouth D, the air in the tube C D, we shall draw into it the water in the vessel A B, so that it will flow out through the projection of the syphon until the water is exhausted. For the air contained between the liquid and the tube E F, being but little, can pass into the tube C D, and the water can then be drawn after it. And the water will not cease flowing because of the projection of the syphon below:—if, indeed, the tube E F were removed, the discharge would cease on the surface of the water arriving at C, in spite of the projection below; but when E F is entirely immersed no air can enter the syphon in place of that drawn off, since the air which enters the vessel takes the place of the water as it passes out.
Fig. 61.
Let A B C [(Fig. 62)], be a bent syphon, or tube, of which the leg A B is plunged into a vessel D E containing water. If the surface of the water is in F G, the leg of the syphon, A B, will be filled with water as high as the surface, that is, up to H, the portion H B C remaining full of air. If, then we draw off the air by suction through the aperture C, the liquid also will follow. And if the aperture C be level with the surface of the water, the syphon, though full, will not discharge the water, but will remain full: so that, although it is contrary to nature for water to rise, it has risen so as to fill the tube A B C; and the water will remain in equilibrium, like the beams of a balance, the portion H B being raised on high, and the portion B C suspended. But if the outer mouth of the syphon be lower than the surface F G, as at K, the water flows out, for the liquid in K B, being heavier, overpowers and draws toward it the liquid B H. The discharge, however, continues only until the surface of the water is on a level with the mouth K, when, for the same reason as before, the efflux ceases. But if the outer mouth of the tube be lower than K, as at L, the discharge continues until the surface of the water reaches the mouth A.
Fig. 62.