46. =Illustrations.=--Many illustrations might be given of this property. I will give a few. If you press a tumbler into water with its open end downward, you can not fill it with water, for the air confined in the tumbler prevents it from rising. It can not occupy the same space with the air. It fills, indeed, a portion of the tumbler, but this is because the air is compressible. If you introduce a glass funnel, _a_, Fig. 6, into a jar of water, _b_, with your thumb on its mouth, _c_, the water will not rise to fill it. But if you take your thumb off, the water will rise to the level of the water outside of the funnel, pushing up the air before it. If you have not a funnel, a vial or bottle with its bottom broken off will answer for the experiment. The following is a very pretty experiment, illustrating the same point. Place a lighted taper, _a_, Fig. 7, on a large flat cork in a jar of water. Put over it an open jar or receiver, _b_, having a stop-cock, _c_. Closing the stop-cock, press the receiver down into the water, and you will see the taper sink with it, as represented in the figure, the air preventing the water from entering the receiver. If now you open the stop-cock the water rushes in, thrusting the air upward, and making the taper to appear as if rising out of the water. The diving-bell offers a good illustration. It consists of a vessel, _a a_, Fig. 8, shaped like a bell, made sufficiently heavy to sink in water. It is let down by a chain and cable, as seen in the figure. The water does not enter the bell any farther than the compressibility of the air permits it. In order that the men in it may remain under water for some time fresh air is supplied by the tube _b_, it being forced down by a forcing-pump. At the same time the vitiated air can be let off by a valve provided for that purpose. There are windows in the top of the bell to give the requisite light for work on the sea's bottom. Treasures are often recovered by this means which would otherwise be lost. You see a resemblance between the diving-bell and the arrangement in Fig. 7, the receiver representing the bell and the lighted taper the men in it.