Figs. 58, 59, 60, 61.—Pressure of Water.
We will now explain the principle of this Water Press. In the small diagram, the letters A B represent the bottom of a cylinder which has a piston fitted in it (P). Into the opposite side a pipe is let in, which leads from a force-pump D, which is fitted with a valve E, opening upwards. When the piston in D is pulled up water enters through the valve; when the piston is forced down the valve shuts, and the water rushes into the chamber A B. The pressure pushes up the large piston with a force multiplied as many times as the area of the small piston is contained in the large one. So if the large one be ten times as great as the small one, and the latter be forced down with a 10 lb. pressure, the pressure on the large one will be 100 lbs., and so on.
Fig. 62.—Water Press.
The accompanying illustration shows the form of the Hydraulic or Bramah Press. A B C D is a strong frame, F the force-pump worked by means of a lever fixed at G, and H is the counterprise. E is the stop-cock to admit the water (fig. 63).
Fig. 63.—Bramah Press.
The principles of hydrostatics will be easily explained. The Lectures of M. Aimé Schuster, Professor and Librarian at Metz, have taught us in a very simple manner the principle of Archimedes, in which it is laid down that “a body immersed in a liquid loses a portion of its weight equal to the weight of the liquid displaced by it.” We take a body of as irregular form as we please; a stone, for example. A thread is attached to the stone, and it is then placed in a glass of water full up to the brim. The water overflows; a volume of the liquid equal to that of the stone runs over. The glass thus partially emptied is then dried, and placed on the scale of a balance, beneath which we suspend the stone; equilibrium is established by placing some pieces of lead in the other scale. We then take a vase full of water, into which we plunge the stone suspended from the scale, supporting the vase by means of bricks. The equilibrium is now broken; to re-establish it, it is necessary to fill up with water the glass placed on the scale; that is to say, we put back in the glass the weight of a volume of water precisely equal to that of the stone.
