A hollow globe, or other vessel, may be constructed, into which if any liquid be poured, it will be forced aloft spontaneously and with much violence, so as to empty the vessel, though such an upward motion is contrary to nature. The construction is as follows. Let there be a globe, containing about 6 cotylæ (3 pints), the sides of which are of metal plate, strong enough to sustain the pressure that will be exerted upon them by the air. Let A B (fig. 9) be the globe, resting on any base C. Through an aperture in the top of the globe insert a tube, D E, soldered into the globe at the aperture, and projecting a little above it; and reaching to the other extremity, except an interval sufficient for the passage of water. At its upper extremity let the tube D E branch into two tubes, D G and D F, to which two other pipes, G H K L, F M N X, are fastened transversely, communicating with D G, D F. Again, into these transverse pipes, and communicating with them, let another pipe, P O, be fitted, from which a small pipe, R S, projects perpendicularly, communicating with it, and terminating in a small orifice at S. If, then, we take hold of R S and turn round the tube P O, the connection between the corresponding holes will be shut off, so that the liquid which is to be forced up will have no outlet. Now, through another aperture in the globe, let another tube, T U Q, be inserted, closed at the lower extremity Q, and having a hole in the side near the bottom at W. In this hole must be fixed a valve, such as the Romans call _assarium_, the construction of which we will explain presently. Into the tube T U Q insert another tube, Y Z, fitting tightly. If the tube Y Z be drawn out, and water poured into T U Q, it will enter the vessel through the aperture W, (the valve opening into the interior of the vessel), and the air will escape through the pipe O P, which communicates, as we have explained, with the apertures of the pipes G H K L and F M N X. When the globe is half full of liquid, turn the small tube R S so as to break the connection between the corresponding apertures: then depress the tube Y Z and drive out the air and liquid collected in T U Q, which will, on the exertion of some force, (as the vessel is full of air and liquid), pass through the valve into the hollow of the globe; and this passage is made possible by the compression of the air into the void spaces dispersed among its particles. Draw up the tube Y Z, in order again to fill T U Q with air, and then, depressing it again, we shall force this air into the globe. By repeating this frequently we shall have a large quantity of air compressed into the globe; for it is clear that the air forced in does not escape again when the rod is drawn up, as the valve, pressed on by the air within, remains closed. If, then, we restore the pipe R S to its upright position, and re-open the communication between the corresponding apertures at L and X, the liquid will now be forced out,