Chapter C: O C I S (4)

1. We have said that the agency of the magnet can be imparted to hard metallic bodies; this may be done in a very easy way. If you pass a magnet (which may be either natural or artificial) over a sewing-needle several times from the eye to the point, the needle will acquire the principle, and attract iron filings in the same manner as a natural magnet would do. But the part of the magnet which you apply to the needle must be the north pole; and you must not pass it over the needle backward and forward, but lift it always from the point and again begin from the eye. Suppose you wish to impart the principle to a small bar of tempered steel, tie the piece to be magnetized to a poker with a piece of silk, and hold the part of the poker to which it is attached in the left hand; take hold of the tongs, a little below the middle, with the right hand, and rub the steel bar with them, moving the tongs from the bottom to the top, and keeping them steadily in a vertical position all the time. About a dozen strokes on each side will impart sufficient magnetic power to the bar to enable the operator to lift up small pieces of iron and steel with it. The lower end of the bar should be marked before it is fastened to the poker, so that the poles may be readily distinguished from each other when it is taken off; the upper end being the south pole, and the lower the north.

2. Scatter some iron filings upon a piece of paper, and hold a magnet underneath it. The instant the contact takes place, the filings will raise themselves upright, and fall down as soon as the magnet is withdrawn. The effect is singular, and indeed very amusing; the diminutive iron particles rising and falling, as if by supernatural agency.

TEST OF MAGNETIC POWER.

To ascertain whether a piece of metal, or mineral, is magnetic, present it to one of the poles of a poised magnet. If it be attracted at both poles, you may then conclude that the substance so tested is not magnetic.

Dip a magnet into boiling water, and it will lose half of its magnetism; but as the magnet cools, its full power will return.

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 pass 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 passed 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 magnetized, and attract iron filings, &c.

HOW TO MAGNETIZE 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.

_Fig. 2._]

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.

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.

VARIATION OF THE NEEDLE.

The magnetic needle does not point exactly north and south, but the north pole of the needle takes a direction considerably to the west of the true north. It is constantly changing, and varies at different parts of the earth, and at different times of the day.

DIP OF THE NEEDLE.

Another remarkable and evident manifestation of the influence of the magnetism of the earth upon the needle is the inclination or dip of the latter, which is a deviation from its horizontal place in a downward direction in northern regions of its north, and in southern regions of its south pole. The causes of the dipping of the needle are yet unexplained. In balancing the needle on the crd, on account of this dipping, a small weight or moveable piece of brass is placed on one end of the needle, by the shifting of which either nearer to or further from the center, the needle will always be balanced.

TO SUSPEND A NEEDLE IN THE AIR BY MAGNETISM.

Place a magnet on a stand to raise it a little above the table; then bring a small sewing-needle containing a thread, within a little distance of the magnet, keeping hold of the thread to prevent the needle from attaching itself to the magnet. The needle in endeavoring to fly to the magnet, and being prevented by the thread, will remain curiously suspended in the air, like Mahommed's coffin.

MAGNETISM BY HAMMERING.

Place a bar of iron in a vertical position, and give it a series of slight blows with a hammer or poker, when it will acquire a feeble degree of magnetism; hence it happens, that the anvils and other tools employed in smithies are endowed with magnetism.

It is, however, a remarkable circumstance, that if you strike a magnet its magnetizing force will be either very much impaired, or altogether destroyed.

Percussion and friction in the required position would seem, from this and preceding experiments, to be the chief means of magnetizing iron and steel. These operations, as it were, waken up the inert particles of the metal to admit new magnetism, or to develop that which already resides in it, originally derived from the earth.

POWER OF THE ELECTRO MAGNET.

The same influence which affects the magnetic needle already described, will also communicate magnetism to soft iron. If a bar of that metal, bent as in the drawing, be surrounded with a common bonnet wire, or a copper wire prevented from touching the iron by a winding of cotton or thread, and then if a current of voltaic electricity be sent through the wire, the bar becomes a powerful magnet, and will continue so as long as the connection with the battery is preserved. On breaking the contact, the magnetism disappears. This experiment may be easily made by the young reader with a horse-shoe magnet, surrounded by several coils of wire. P is the positive and N the negative pole.

THE MARINER'S COMPASS.

The mariner's compass is an artificial magnet fitted in a proper box, and consists of three parts--1, the box; 2, the card or fly; and 3, the needle. The box is suspended in a square wooden case, by means of two concentric brass circles called gimbals, so fixed by brazen axes to the two boxes, that the inner one, or compass-box, retains a horizontal position in all motions of the ship. The card is a circular piece of paper which is fastened upon the needle, and moves with it. The outer edge of the card is divided into thirty-two points, as shown in the engraving, called points of the compass. The needle is a slender bar of hardened steel, having a hollow agate cup in the center, which moves upon the point of a pivot made of brass.

TO MAKE ARTIFICIAL MAGNETS WITHOUT THE AID EITHER OF NATURAL LOADSTONES OR ARTIFICIAL MAGNETS.

Take an iron poker and tongs, or two bars of iron, the larger and the older the better, and fixing the poker upright, hold to it with the left hand near the top P by a silk thread, a bar of soft steel about three inches long, one fourth of an inch broad, and one twentieth thick; mark one end, and let this end be downwards. Then grasping the tongs T with the right hand a little below the middle, and keeping them nearly in a vertical line, let the bar B be rubbed with the lower end L of the tongs, from the marked end of the bar to its upper end, about ten times on each side of it. By this means the bar B will receive as much magnetism as will enable it to lift a small key at the marked end; and this end, the bar being suspended by its middle or made to rest on a joint, will turn to the north, and is called its north pole, the unmarked end being the south pole. This is the method recommended by Mr. Caxton, in his process, which he regarded superior to those in former use, and of which a more detailed account will be found in his interesting volume.

THE WATCH MAGNETIZED.

Borrow a watch from the company, and inquire if it will go when laid on the table. Then place it just over the point at which a magnet is fixed underneath the top of the table, and the magnet will attract the balance-wheel of the watch, and cause it to stop.

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.

POLARITY OF THE MAGNET.

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 center 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 compass. 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.

MAGNETIC ACTION AND REACTION.

A magnet and a piece of iron attract each other equally, whatever disproportion there is between their sizes. If either be balanced in a scale, and the other be brought within a certain distance beneath it, the very same counterpoise will be required to prevent their approach, whichever be in the scale. If the two were hanging near each other, as pendulums, they would approach and meet, but the little one would perform more of the journey in proportion to its littleness.

TO PASS MAGNETISM THROUGH A BOARD.

Place a common sewing-needle on a smooth horizontal board, and move a strong magnet underneath the board, when the needle will revolve along the board, according to the peculiar motion given to the magnet.

THE MAGNETIC TABLE.

Under the top of a common table, place a magnet that turns on a pivot, and fix a board under it that nothing may appear. There may also be a drawer under the table, which you pull out, to show that there is nothing concealed. At one end of the table there must be a pin that communicates with a magnet, and by which it may be placed in different positions; this pin must be so placed as not to be visible to the spectators. Strew some steel filings, or very small nails, over that part of the table where the magnet is. Then ask any one to lend a knife, or a key, which will then attract part of the nails or filings. Then placing your hand, in a careless manner, on the pin at the end of the table, you alter the position of the magnet; and giving the key to any person, you desire him to make the experiment, which he will then not be able to perform. You then give the key to another person, at the same time placing the magnet, by means of the pin, in the first position, when that person will immediately perform the experiment.

INTERESTING PARTICULARS CONCERNING THE MAGNET.

Fire-irons which have rested in one position in a room during the summer months are often highly magnetic.

Iron bars standing erect, such as the gratings of a prison cell, or the iron railings before houses, are often magnetic.

The uppermost of the iron tires round a carriage wheel attracts the north end of a magnet, and has hence south polarity, while the lower end attracting the south end of the same, has north polarity.