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Example I: Boil

Get a vessel of hot water, and put a phial into it, with the mouth downwards; the expanded air will bubble out. Let the water cool, or pour cold water on the phial, of which the mouth has not been drawn above the surface of the water, and as the air is now cooled, and occupies less space, a considerable part of the bottle will be filled with water. Boil a little water in a glass phial cver a candle for a few minutes; then invert the mouth of the phial in water, and, as it cools, the air will contract, and water will be forced up the bottle, by the external air, to occupy the vacant space. Lay a weighty book on a bladder, and blow into it with a pipe, and the book will be raised. Increase the weight on the bladder very much indeed, and you may still raise it as before. A bladder filled with air may be compressed, and the moment the force is removed, it will recover its size If thrown on the ground it will rise like a ball.

Take a cup, and burn a few pieces of paper in it, the heat will expand the air in it. Invert the cup now in a saucer of water, and, as the enclosed air cools, it will return to its former density, and leave a vacuum, and the pressure of the external air will force a great deal of water up into the cup. If this experiment be performed with a large drinking-glass, the water may be seen to rise in the glass.

The pressure of the air may be very sensibly felt, by putting the hole of a common bellows over the knee, and then attempting to raise the upper part of it. Boil water in a glass phial over a candle for a few minutes, then suddenly removing it, tie a piece of wetted bladder over the mouth, making it fast with a string; the pressure of the air will stretch the bladder, if it do not burst it. Get a glass vessel, as a common tumbler, if no better be at hand, and put a piece of wetted bladder over the mouth, pressing it down in the middle, and then tie it firm with a string; then lay hold of the bladder in the middle, and try to pull it straight, or level with the rest, and the pressure of the external air will not permit it.

Do exactly the same as before, except that the vessel must be nearly full of water. Turn the vessel upside-down, and the bladder will still continue as it was placed, the pressure of the air overcoming the weight of the water.

Though air be capable of compression, it makes a resistance, and that very considerable. The ball of an air-gun has been burst asunder by overcharging it. If bottles are filled too much, they may be burst in attempting to cork them, from the air between the cork and the liquor being too much condensed. Put a common wine-glass, with the mouth downwards, into water; and to whatever depth it may be plunged, the air will not allow much water to rise into it, as may be seen by the inside of the glass not being wet. If a bit of cork float inside of the glass, it will point out to the eye still more clearly how high the water rises. This experiment, though so very simple, will illustrate the nature of the diving-bell.

Experiments respecting Sound.

Hold a tumbler sideways, and sprinkle a little dust, or powder of any sort, on it; then strike the glass, and make it sound:-the dust keeps dancing about whilst the sound continues; stop the sound, and the dust is at rest. The sound of a watch laid upon a long table, or upon a plank of wood, will be heard much farther than it otherwise would.

When a vessel on the fire begins to boil, let a communication be made between it and the ear, by means of the poker, and the sound is more distinctly heard.

Tie a string round the end of a poker, and then, winding one end of the string round the fore-finger of the one hand, and the other end of the string round the fore-finger of the other; put the fingers into the ears, and make the poker strike against a table, or any other object, and it will sound like the bell of a church.

Tie a string round the end of a poker, as before, and hold the string with your teeth; when the poker is made to strike against any object, as in the last experiment, the same kind of sound will be transmitted through the teeth.

Make a watch touch your teeth, and you will hear its beating more distinctly. When a pitchfork is struck, in order to pitch a tune, its end is put on the table, and a greater sound is produced. If the pitchfork, after being struck, be held to the teeth, its sound is still more distinct.

Having shut up both ears with cotton very closely, put your fingers on the teeth of a person who speaks to you, and you will hear his voice.

Electrical Experiments.

If a piece of sealing-wax be rubbed briskly against the sleeve of your coat, or any other woollen substance, for some time, and then held within an inch or less of hair, feathers, bits of paper, or other light bodies; they will be attracted, If a tube that is, they will jump up, and adhere to the wax. If a tube wax. of glass, or small phial, be rubbed in a similar manner, it will answer much better. The bottle thus rubbed becomes electric; and when the operation is performed in a dark room, small flashes of divergent flame, ramified somewhat like trees bare of leaves, will dart into the air, from many parts of the surface of the tube, to the distance of six or eight inches, attended with a crackling noise; and sometimes sparks will fly along the tube to the rubber at more than a foot distant.

Cut two bits of cork into the shape and size of a common pea. With a needle, draw a thread through each of the corks, so that they may be made to hang at the ends of the threads with a knot below them. Let the other ends of the threads be inserted in the notch of a small piece of wood, about a foot long, and an inch broad, and the thickness of a common match. Lay the piece of wood over two wineglasses, a few inches asunder so that the end of it, in which the threads are, may project over the edge of the glass nearest it, and the corks may be in contact one with another. Take another wine-glass, and, having rubbed it briskly with a piece of flannel, or upon the skirt or sleeve of a woollen coat, hold its mouth to within about an inch of the corks, and they will suddenly start asunder, and continue so for some time.

Lay a pocket-watch upon a table, and take a common tobacco pipe, and place it on the face of the watch so that it may balance thereon; then, after rubbing a wine-glass, as described in the former experiment, bring it to within an inch of the smaller end of the tobacco-pipe, and by moving the glass gently round in an horizontal circular track, you will cause the pipe to turn round on the watch-glass, as the needle turns on its centre in a mariner's compass.