_The Mysterious Watch._

Desire any person to lend you his watch, and ask if he thinks it will or will not go when it is laid on the table: if he says it will, place it over the end of a magnet, and it will presently stop; then mark with chalk, or a pencil, the precise point where you placed the watch, and, moving the position of the magnet, give the watch to another person, and desire him to make the experiment; in which he not succeeding, give it to a third person, at the same time replacing the magnet, and he will immediately perform the experiment.

_To make a Gla.s.s of Water appear to boil and sparkle._

Take a gla.s.s nearly full of water, or other liquor, and setting one hand upon the foot of it to hold it fast, turn slightly one of the fingers of your other hand upon the brim or edge of the gla.s.s, (having before privately wet your finger,) and so pa.s.sing softly on, with your finger pressing a little, then the gla.s.s will begin to make a noise, the parts of the gla.s.s will sensibly appear to tremble with notable rarefaction and condensation, the water will shake, seem to boil, cast itself out of the gla.s.s, and leap out by small drops, to the great astonishment of the observers, if they are ignorant of the cause, which is only the rarefaction of the parts of the gla.s.s, occasioned by the motion and pressure of the finger.

_How to make a Cork fly out of a Bottle._

Put a little chalk or pounded marble into a phial, and pour on some water, with about a third part of sulphuric acid, and put in a cork: in a few seconds, the cork will be sent off with great violence.

_To produce Gas Light, on a small Scale._

Take an ordinary tobacco pipe, and nearly fill the bowl with small coals, and stop the mouth of the bowl with any suitable luting, as pipe-clay, or the mixture of sand and common clay, or, as clay is apt to shrink, of sand and beer, and place the bowl in a fire between the bars of a grate, so that the pipe may stand nearly perpendicular. In a few minutes, if the luting be good, the gas will begin to escape from the stem of the pipe, when, if a piece of lighted paper or candle be applied, it will take fire and burn for several minutes with an intense light. When the light goes out, a residuum of useful products will be found in the bowl.

_Thunder Powder._

Take separately, three parts of good dry saltpetre, two parts of dry salt of tartar, and pound them well together in a mortar; then add thereto one part, or rather more, of flour of brimstone, and take care to pound and mix the whole perfectly together: put this composition into a bottle with a gla.s.s stopper, for use.

Put about two drams of this mixture in an iron spoon, over a moderate fire, but not in the flame; in a short time it will melt, and go off with an explosion like thunder or a loaded cannon.

_To tell, by the Dial of a Watch, at what hour any Person intends to rise._

Let the person set the hand of the dial to any hour he pleases, and tell you what hour that is, and to the number of that hour you add, in your mind, 12. After this, tell him to call the hour the index stands at that which he has fixed upon; and by reckoning backwards from this number to the former, it will bring him to the hour required.

EXAMPLE.

Suppose the hour at which he intends to rise be 8, and that he has placed the hand at 5.

Then, adding 12 to 5, you bid him call the hour at which the index stands, the number on which he thought; and by reckoning back from this number to 17, it will bring him to 8, the hour required.

_The following Experiment shews the Power of Attraction._

If we take two pieces of lead, as two musket or pistol b.a.l.l.s, and with a knife smooth two plane surfaces, and press them together, they will firmly adhere.

Two plates of metal made very smooth, when rubbed with oil and put together, will so firmly adhere, that it will require a great force to separate them.

If two pieces of wood, or of gla.s.s, be wetted with water, and placed together, the one may be lifted up by means of the other. Boys often have a piece of leather on the end of a string, which they wet and put on a stone, and thereby lift it up.

If we take a small tube of gla.s.s with a narrow bore, and put it in water, the fluid will rise higher within the tube than in the vessel. The narrower the tube is, the higher the water rises. This is called Capillary Attraction. If we put two pieces of gla.s.s together, and place the lower edge in water, it will rise between them, as it does in the capillary tubes. This experiment may be made more pleasing, by putting a shilling or a piece of paper between the two pieces of gla.s.s at one end. The water will then rise in a curve line, called an hyperbola, higher and higher as it recedes from the shilling or piece of paper, and the pieces of gla.s.s get nearer to each other.

Place a balance equally poised, so that one scale may be made to touch water in a vessel; considerable weight must be put in the other scale, to make it rise up. Put three or four bits of cork to float in a basin of water; they will gradually draw nearer to each other, and the more rapidly as the distance diminishes.

_Experiments to shew the Power of Repulsion._

Dip a ball in oil and put it in water; a ditch will be formed all round it. Pour water on oiled paper, and it will run off.

Sprinkle water on a dusty floor, it rolls over it in globules. Sprinkle it upon a floor that has been swept, and this will not be the case, as it then comes in contact with the wood, and is diffused over it.

We may observe that rain water stands in globules on the leaves of cabbages. If we blow up soap-bubbles, and let them fall on the carpet, they will not for some time burst. Let them fall on the table, or any smooth surface, and they will burst instantly.

If we pour as much water into a cup as it will possibly hold, we shall see the water above the level of the sides, if the edge be dry, but otherwise we shall not.

Lay a very fine needle, or a piece of tinfoil, on the surface of water, and it will float, until it become wet, when it sinks.

Lay a piece of gold on mercury, and it will float on the surface; but if depressed below the surface, it will sink to the bottom, like the needle on water.

_Experiments respecting the Centre of Gravity._

The centre of gravity is that part of a body, round which all its parts are so equally balanced, that, if it be supported, the whole body will be so too.

Take a book, and find, by trial, under what part the finger must be placed to keep the book from falling; that point is the centre of gravity.

Take a rod, or stick, and find that place about the middle of it, under which the finger being placed, it will be balanced; that is the centre of gravity. The moment the centre of gravity ceases to be supported, the whole body falls.

Move a piece of board to the edge of a table, and gradually farther and farther off it; the instant the centre of gravity gets beyond the edge of the table, the board falls.

Run the point of a knife much slanting into the same board, it may then be brought much farther over the edge of the table than it could before, as the knife, leaning the way of the table, brings the centre of gravity that way.

Take a bottle, with a cork in it; stick in the middle of the cork a needle, with the point, upwards; then take another cork, and with a knife make a slit in one of its ends, in which place a shilling so far as to make it fast; then take two forks, or penknives, and stick one on each side the cork, slanting a little downwards; then place the edge of the shilling on the point of the needle, and it will rest secure. It may be made to revolve, with great rapidity, on the point of the needle, without falling off.

_The following Experiment shews the Power of Steam._

Put a little water in a bottle, and cork it securely, covering it with sealing wax; then put the bottle into a kettle of water, and let it boil a short time, and the steam will force out the cork.

_Diminution of Heat by Evaporation._

Pour water on a piece of writing-paper, and hold it over a candle; it will boil without burning the paper.

Water may be boiled in an egg-sh.e.l.l on the fire.

_Experiment to ascertain the Strength of Spirits of Wine._

It is a common practice for apothecaries, in order to ascertain if spirit of wine be sufficiently strong, to pour some into a cup upon some gunpowder, and then to set fire to it. If the spirit be sufficiently strong, after burning down to the gunpowder, it will make it go off; but if too much water has been poured in, that will not take place, as, after the spirit is consumed, there will still be water enough to keep the powder wet.

_To ascertain the Strength of Brine._