we may infer that the upward pressure at any point below the surface of a liquid is equal to the downward pressure.
Demonstrations. - Select a glass tube, like a lamp chimney, and a glass plate or.disk just large enough to cover the end of the tube. Grind the end of this tube, and the glass plate, to a water-tight joint with emery. Fasten three cords to the plate or disk, and to a single cord, as in Fig. 1. Hold the disk in place over the bottom of the tube with the cord, and push the tube down into the water in a jar. The upward pressure will hold the disk in place without the cord. Pour water into the tube until the disk falls off; then the weight of the water poured in, added to the weight of the disk, will measure the upward pressure.
Place in the bottom of a shallow pan a piece of smooth glass, and stand upon it a heavy lamp chimney of the form shown in Fig. 2 , with the lower end ground smooth. Pour water into the chimney, and observe that when it rises to some definite point, А, it will not rise any farther because it runs out at the bottom. If the chimney is held down by placing a finger on the top and it is then filled with water, it will remain full as long as it is held down, but when the finger is removed, the water suddenly drops to A and stops there. What is the effect of the upward pressure of the water on the collar of the chimney in this demonstration?
FIG2
