The inelastic nature of water causes it to retain its surface perfectly level ; were it otherwise, vessels would often run aground, where, at present, they find depth sufficient to float them ; and the whole body of a river would present a thousand opposing and unequal resistan ces ; whereas we find the resistance to be uniform. To prove this, let a piece of wood be put into a pail of water, the fluid will in every' part remain equally dense, and the surface will be perfectly level. For a further elucidation of this property, we refer to HYDROSTATICS, wherein it will be found very conspicu ous.
The ingenious Mr. Bramah has lately applied the inelasticity of water to a va riety of purposes, especially in the ap plication of a power to remote effects.— Thus, if water be filled into the pipe, AB C D, fig. 3, and that a piston be applied to A B, made perfectly tight, so that no water can possibly escape, when that pis ton is pressed down by means of a force cvpable of overcoming the friction of its sides, and the friction of the water within the tube, it will cause the water to rise in the pipe, C D, whatever may be the length of the conjunctive part, A C.— Therefore, if a piston is inserted into the pipe C D, it will be acted upon in perfect conformity with the motion of the piston in A B ; the power to move which may be trifling, when the diameter of the pipe is small, and the purpose not relating to forcible operations, Thus, for the mere intention of ringing a bell at D, a hundred yards distant from the pull, A, a bore of less than a quarter of an inch in diameter would answer every purpose, and yield to the pressure of the finger, with very little exertion. On the other hand, when machinery is to be set in motion, the size of the piston, and the force whereby it is to be moved, must be pro portioned to the resistance generated by friction, and by the opposition to the ac tion of the machine. It is necessary to ob serve, that where the two pistons are of equal diameter, their actions will be. equal ; but that if the pipe, A B, be larg er than C D, it willproduce an increased action in the latter, which, in such case, must have a proportionate increase of al titude, and, vice versa, when the action of A 13 is to be greater than that of C D.— Our readers will be sensible that a tube of less diameter can be made to contain the same quantity as that of greater capacity, only by adding to its length ; and that both their areas being filled and emptied alternately by the same action, and in the same time, that which has the greatest al titude must have the greatest scope of action, and move with an increased velo city in exact ratio with the difference of the diameters. When the velocity of the
machinery attached to the movement tube is to be diminished, without losing the height to which the secondary power is thus raised by the additional length of the tube, the segment on which it is made to act must be that of a larger cir cle, as shewn in fig. 4, where the tube, A 13, is of double the diameter of that at C D, which would raise the lever, E, to the height F. Now, if this lever were the handle of a pump, requiring a considera ble exercise of power, it is evident the fulcrum, G, must be placed very near to the pump-tube, H ; whereby the radius of the circle, G F, is greatly increased, and the plonge of the pump-piston, H, much di: minished. If, on the contrary, the fulcrum had been at 0, i. e. dividing the distance between D and X into three parts, of which two are given to the lever, N, the plonge would be far deeper, but the power would be greatly reduced ; the segment,ID F, occupying a greater angle with the fulcrum 0, than it does with the fulcrum G. This is amply explained un der the head of MECHANICS.
Where water is enclosed within a ves sel, or in a tube, in such manner that air cannot penetrate, it will not flow out in the same manner, as if air were admitted to supply the place of any quantity that might be required to be drawn off. Of this every person must be sensible who has ever attempted to draw wine, beer, &c. from a full cask, without opening a vent at the top, near the bung, to admit air, as the fluid might evacuate the upper part of the vessel From this we prove, that although all fluids have a direct dis position to gravitation, they are perfectly inelastic ; if they were otherwise, we should find that, by expansion, they would be capable of filling a greater or lesser space at times ; and that as the wine, &c. were drawn off below, the portion re maining in the vessel would expand, and, though less dense, would fill the whole interior.