Hydraulic Ram.

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Chap. 1.]

drive a portion of the liquid far above the source whence it flows, is obvi-ous from several operations in nature. Düring a storm of wind, longswelling waves in the open sea alternately rise and fall, without the crestsor tops of any being elevated much above those of the rest; but whenthey meet from opposite directions, or when their progress is suddenlyarrested by the bow of a ship, by rocks, or other obstacles, part of thewater is driven to great elevations. There is a fine example of this at theEddystone rocks —the heavy swells from the Bay of Biscay and from theAtlantic, roll in and break with ineonceivable fury upon them, so that vo-lumes of water are thrown up with terrific violence, and the celebratedlight-house sometimes appears from this cause like the pipe of a fountainenclosed in a stupendous jet d’eau. The light room in the old light-housewas sixty feet above the sea, and it was often buried in the waves, so im-mense were the volumes of water thrown over it.

The hydraulic ram raises water on precisely the same principle : aquantity of the liquid is set in motion through an inclined tube, and its es-cape from the lower orifice is made suddenly to cease, when the momen-tum of the moving mass drives up, like the waves, a portion of its ownvolume to an elevation much higher than that from which it descended.This may be illustrated by an experiment familiär to most people. Sup-pose the lower orifice of a tube (whose upper one is connected to a reser-voir of water) be closed with the finger, and a very minute stream be al-lowed to escape from it in an upward direction—the tiny jet would risenearly to the surface of the reservoir; it could not, of course, ascendhigher—but if the finger were then moved to one side so as to allow afree escape tili the whole contents of the tube were rapidly moving to theexit, and the orifice then at once contracted or closed as before, the jetwould dart far above the reservoir; for in addition to the hydrostatic pres-sure which drove it up in the first instance, there would be a new forceacting upon it, derived from the motion of the water. As in the case ofa hammer of a few pounds weight, when it rests on the anvil it exerts apressure on the -latter with a force due to its weight only, but when putin motion by the hand of the smith, it descends with a force that is equiva-lent to the pressure of perhaps a ton.

Every person accustomed to draw water from pipes that are suppliedfrom very elevated sources, must have observed, when the cocks or dis-charging orifices are suddenly closed, a jar or tremor communicated to thepipes, and a snapping Sound like that from smart blows of a hammer. Theseeffects are produced by blows which the ends of the pipes receive fromthe water; the liquid particles in contact with the plug of a cock, when itis turned to stop the discharge, being forcibly driven up against it by thoseconstituting the moving mass behind. The philosophical instrument nameda water hammer illustrates this fact. The effect is much the same as if asolid rod moved with the same velocity as the water through the tubeuntil its progress was stopped in the same manner, except that its mo-mentum would be concentrated on that point of the pipe against which itStruck, whereas with the liquid rod the momentum would be communi-cated equally to, and might be transmitted from any part of, the lower endof the tube; hence it often occurs that the ends of such pipes, when madeof lead, are swelied greatly beyond their original dimensions. We haveseen some f of an inch bore, become enlarged to 1J inches before they wereruptured. At a hospital in Bristol , England, a plumber was employedto convey water through a leaden pipe from a cistern in one of the upperStories to the kitchen below, and it happened that the lower end of thetube was burst nearly every time the cock was used. After several at-