The Boy's Playbook of Science / Including the Various Manipulations and Arrangements of Chemical and Philosophical Apparatus Required for the Successful Performance of Scientific Experiments in Illustration of the Elementary Branches of Chemistry and Natural Philosophy

by John Henry Pepper

Fig. 241.

The curved lines of magnetic force.

The heavy glass already alluded to, upon which the magnet exerts a certain influence, is called

THE DIA-MAGNETIC;

and by this term is meant a body through which the lines of magnetic force are passing without affecting it like iron or steel. At [page 211] is a picture representing (at Figs. 201 and 202) the direction of the electricity and that of the magnetic current or whirl at right angles to it. If, then, Fig. 202 be considered as a piece of glass, the arrow a b will show "the line of magnetic force," the point b being the north pole, and the shaft a the south pole of the magnet, and the arrows traced round will represent direction. This simple drawing expresses the whole of the law of the action of the magnet on the glass, and if kept in view, will give every position and consequence of direction resulting from it.

The phenomenon of the affection of the beam of polarized light is immediately connected with the magnetic force, and this is supposed to be proved by the brightness of the polarized ray being developed gradually, as the iron coiled with wire requires about two seconds to acquire its greatest power after being connected with the battery.

In another experiment of Faraday's, where a beam of polarized light was sent through a long glass tube containing water, and introduced as a core inside a powerful electro-magnetic coil, the image of a candle viewed with a proper eye-piece, appeared or disappeared as the battery connexion was made or broken with the coil; but this result is not considered by many philosophers to be conclusive of the action of magnetism on light, but rather as an alteration of the refracting power of the medium through which the light passes. These experiments were the precursors of the other effects of magnetism upon different kinds of matter which Faraday discovered, and he commenced his examination with a small bar of heavy glass suspended by a filament of silk between the poles of an electro-magnet, and when the twisting or effects of torsion had ceased, the battery was connected. Directly the current passed, Faraday's keen eye detected a movement of the glass, and on repeating the experiment, he discovered that the movement was not accidental, but always took place in a certain fixed direction—viz., a direction at right angles to a line drawn across and touching the two poles of a horse-shoe-shaped magnet—i.e., supposing the feeder or bit of soft iron usually placed in contact with the poles of the horse-shoe-magnet to represent the "axial line," any line drawn across it at right angles would be called the equatorial line, whilst the general space included between the poles of the magnet is called "the magnetic field." The movement of the heavy glass was therefore equatorial, and it pointed east and west instead of north and south, like iron and steel.

Fig. 242.