Cement a piece of wood into the lower part of the neck of an open receiver, and pour mercury over it. After a few strokes of the pump, the pressure of the air on the mercury will force it through the pores of the wood in the form of a beautiful shower. If you take care that the receiver is clear and free from spots or dust, and it is dry weather, it will appear like a fiery shower, when exhibited in a dark room.
Magic Fountain.
Take a tall glass tube, hermetically sealed both at top and bottom, by means of a brass cap screwed on to a stop-cock, and place it on the plate of the pump. When the air is exhausted, turn the cock, take the tube off the plate, and plunge it into a basin of mercury or water. Then the cock being again turned, the fluid, by the pressure of the air, will play upon the tube in the form of a beautiful fountain.
The Exploded Bladder.
Take a glass pipe open at both ends, to one of which tie fast a wet bladder, and let it dry. Then place it on the plate of the pump. While the air presses the bladder equally on both sides, it will lie even and straight; but as soon as the air is exhausted, it will press inwards, and be quite concave on the upper side. In proportion as the air is exhausted, the bladder will become more stretched; it will soon yield to the incumbent pressure, and burst with a loud explosion. To make this experiment more easy, one part of the bladder should be scraped with a knife, and some of its external fibres taken off.
The Cemented Bladder.
Tie the neck of the bladder to a stop-cock, which is to be screwed to the plate of the pump, and the air exhausted from the bladder; then turn the stop-cock, to prevent the re-entrance of the air, and unscrew the whole from the pump. The bladder will be transformed into two flat skins, so closely applied together, that the strongest man cannot raise them half an inch from each other; for an ordinary-sized bladder, of six inches across the widest part, will have one side pressed upon the other with a force equal to 396 pounds' weight.
Cork heavier than Lead.
Let a large piece of cork be pendent from one end of a balance beam, and a small piece of lead from the other; the lead should rather preponderate. If this apparatus be placed under a receiver on the pump, you will find that when the air is exhausted, the lead, which seemed the heaviest body, will ascend, and the cork outweigh the lead. Restore the air, and the effect will cease. This phenomenon is only on account of the difference of the size in the two objects. The lead, which owes its heaviness to the operation of the air, yields to a lighter because a larger substance when deprived of its assistance.