HYDRAULICS.

The science of Hydraulics comprehends the laws which regulate non-elastic fluids in motion, and especially water, &c.

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Water can only be set in motion by two causes--the pressure of the atmosphere, or its own gravity. The princ.i.p.al law concerning fluids is, that they always preserve their own level. Hence water can be distributed over a town from any reservoir that is higher than the houses to be supplied; and the same principle will enable us to form fountains in a garden, or other place. Should any of our young friends wish to form a fountain, or jet d'eau, they may, by bringing a pipe from T, a water-tank, which should be at the upper part of the house, convey the water down to the garden. Then by leading it through the earth, underneath the path or gra.s.s-plot, and turning it to a perpendicular position, the water will spring out, and rise nearly as high as the level of that in the tank. The part of the pipe at B should have a turnkey, so that the water may be let on or shut off at pleasure.

THE SYPHON.

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The syphon B is a bent tube, having one leg shorter than the other. It acts by the pressure of the atmosphere. In order to make a syphon act, it is necessary first to fill both legs quite full of the fluid; and then the shorter leg must be placed in the vessel to be emptied.

Immediately upon withdrawing the finger from the longer leg, the liquor will flow. Any young person may form a syphon by a small piece of leaden pipe, bent into the form above.

THE PUMP.

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The action of the common pump is as follows: When the handle A is raised, the piston-rod B descends, and brings the piston-valve, called the sucker, or bucket, to another valve, C, which is fixed, and opens inwards towards the piston. When the handle is drawn down, the piston is raised, and, as it is air-tight, a vacuum is produced between the two valves; the air in the barrel of the pump, betwixt the lower valve and the water, then forces open the lower valve, and rushes through to fill up this vacuum; and the air in the pump being less dense than the external atmosphere, the water is forced a short way up the barrel. When the piston again descends to the lower valve, the air between them is again forced out by forcing open the upper valve; and when the piston is raised, a vacuum is again produced, and the air below the lower valve rushes up, and the water in consequence is again raised a little further. This operation continues until the water rises above the lower valve; at every stroke afterwards, the water pa.s.ses through the valve of the descending piston, and is raised by it, on its ascent, until it issues out of the spout.

THE HYDRAULIC DANCER.

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Make a little figure of cork, in the shape of a dancing mountebank, sailor, &c. In this figure place a small hollow cone, made of thin leaf bra.s.s. When this figure is placed upon any jet d'eau, such as that of the fountain recommended to be constructed, it will be suspended on the top of the water, and perform a great variety of amusing motions. If a hollow ball of very thin copper, of an inch in diameter, be placed on a similar jet, it will remain suspended, turning round and spreading the water all about it.

THE WATER SNAIL, OR ARCHIMEDEAN SCREW,

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may easily be constructed. Purchase a yard of small leaden pipe, and twist it round a pole, as in the following figure, A; place a handle at its upper end, B, and let its lower end rest in the water. Between the last turn of the pipe and the orifice place a paddle-wheel, C. Now, should the water be that of a running stream, the force of the stream will turn the pipe, and the water will rise in it till it empties itself into the trough at D. Should the water have no motion, the turning of the handle at B will elevate the water from the lower to the higher level.

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MAGNETISM.

The attractive power of the loadstone has been known from a very remote period. The natural magnet appears native in a grey iron ore in octahedral crystals, composed of 168 parts of iron, and 64 parts of oxygen, Fe3O4. Its properties seem to have been studied in Europe during the dark ages, and a directive power is alluded to by Cardinal James de Vitri, who flourished about the year 1200, who observed, that it was indispensable to those who travel much by sea.

In modern times, the history as well as the nature of the magnet has engaged remarkable attention; and it has been determined beyond all dispute that the magnet was used by the Chinese under the name of the _tche-chy_ (directing-stone) about 2604 years before Christ. It pa.s.sed from them to the Arabs, and was first used in Europe after the Crusades; and Ludi Vestoma.n.u.s a.s.serts, that about the year 1500 he saw a pilot in the East Indies direct his course by a magnetic needle like those now in use.

RELATION OF MAGNETISM TO ELECTRICITY.

The most remarkable theories have been invented to account for the phenomena of magnetism. Halley imagined magnetic globes to be moving to and fro in the interior of the earth. Barlow's theory, which refers the whole to electrical currents, is the most rational. Dr. Faraday, for whose kindness to us in early days we always feel grateful, in a series of very curious experiments, has succeeded in identifying magnetism with galvanism, by directing galvanic currents at right angles to the direction of powerful magnets. And its connexion with this and the common species of electricity has deprived it of all its conjuring powers, and reduced it to the well-defined action of electrical bodies.

It is not for us to write either a history of this interesting subject, or to treat it as a science to be acquired; but as it embodies a great number of most instructive and amusing experiments, we think it proper to introduce it here.

TO MAKE ARTIFICIAL MAGNETS.

This may be done by stroking a piece of hard steel with a natural or artificial magnet. Take a common sewing-needle and pa.s.s the north pole of a magnet from the eye to the point, pressing it gently in so doing.

After reaching the end of the needle the magnet must not be pa.s.sed back again towards the eye, but must be lifted up and applied again to that end, the friction being always in the same direction. After repeating this for a few times the needle will become magnetised, and attract iron filings, &c.

HOW TO MAGNETISE A POKER.

Hold it in the left hand in a position slightly inclined from the perpendicular, the lower end pointing to the north, and then strike it smartly several times with a large iron hammer, and it will be found to possess the powers of a magnet, although but slightly.

TO SHOW MAGNETIC REPULSION AND ATTRACTION.

Suspend two short pieces of iron wire, N S, N S, so that they will hang in contact in a vertical position. If the north pole of a magnet N be now brought to a moderate distance between the wires, they will recede from each other, as in figure 1.

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The ends S S being made south poles by induction from the north pole N, will repel each other, and so will the north poles N N. This separation of the wires will increase as the magnet approaches them, but there will be a particular distance at which the attractive force of N overcomes the repulsive force of the poles S S, and causes the wires to converge, as in figure 2; the north poles N N still exhibiting their mutual repulsion.

NORTH AND SOUTH POLES OF THE MAGNET.

Each magnet has its poles, north and south--the north or south poles of one magnet, repel the north and south pole of another. If a magnet, as in the following figure, be dipped in some iron filings, they will be immediately attracted to one end. Supposing this to be the north pole, each of the ends of the filings, not in contact with the magnet, will become north poles, while the ends in contact will by induction become south poles. Both will have a tendency to repel each other, and the filings will stand on the magnet as in the figure.

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POLARITY OF THE MAGNET.

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The best method of proving this is to take a magnet or a piece of steel rendered magnetic, and to place it on a piece of cork by laying it in a groove cut to receive it. If the cork be placed in the centre of a basin of water, and allowed to swim freely on its surface, so that it is not attracted by the sides of the basin, it will be found to turn its north pole to the north, and its south pole to the south, the same as the mariner's compa.s.s. If you fix two magnets in two pieces of cork, and place them also in a basin of water, and they are in a parallel position with the same poles together, that is, north to north, and south to south, they will mutually repel each other; but if the contrary poles point to one another, as north to south, they will be attracted.

THE MAGNETIC FISH.

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Fish are to be purchased at the toy-shops, by which the young "magnetique" may perform this experiment; they are made hollow, and will float on the water. In the mouth of each should be inserted a piece of magnetic wire. The angling rod is like any other rod, and has a silken thread for a line, and an iron hook also strongly magnetised. To catch the fish it is only necessary to put the hook in contact with the noses of the fish, and they will be taken without any of the baits mentioned in the former part of this work.

THE MAGNETIC SWAN.

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The figure of a swan should be cut in cork, and within its beak a small strongly magnetised piece of steel should be placed. The swan should then be covered with a coating of white wax, and fashioned further into the shape of a swan, and gla.s.s beads may be placed in its head for eyes.