Page:Popular Science Monthly Volume 12.djvu/578

560 If a wire, from a galvanic battery such as is shown in Fig. 1, through which a current of electricity is passing, be wound around a piece of steel or soft iron, as represented in Fig. 2, some curious things will happen. If the bar be soft iron, it will be made magnetic, and kept in that condition as long as the current continues to pass round it, and its ends will then attract and hold bits of iron, but drop them when the battery is taken away. If the bar be of steel, instead of soft iron, it will be magnetized and attract iron just as before; but, unlike the soft-iron bar, it will keep its magnetism and attract the iron even after the battery is removed. Its magnetism will be permanent. Since, however, electricity made the magnet, we can, in turn, make the magnet a source of electricity. Suppose the magnetized steel bar has attracted and is holding on to a piece of iron. We can now take the battery away and join the ends of the wire, as in Fig. 8; then, if the piece of iron be pulled off and stuck on again, a current of electricity will run through the wire every time it is done. Electricity produced in this way is called magneto-electricity, and the current in the wire is said to be an induced electric current. If, now, the wire from bar No. 1 (Fig. 4), be extended to a distance, and coiled around another magnetized bar (No. 2), the currents induced in it, by making and breaking the contact of the piece of soft iron with the first magnet, will simultaneously affect the magnetism in the distant magnet also. Though the magnets be a mile or a hundred miles apart, the disturbance in one is immediately and equally manifested in the other.

But, what is still more remarkable, these induced currents may be sent through the wire without the actual contact of the soft iron with the steel bar. If this piece of iron is brought very near to one magnet without touching it, and then withdrawn, an electric thrill or wave is induced in the wire which is felt in the distant magnet, just as if the contact had been actually made and broken. And so if we play the piece of soft iron backward and forward, before the magnet, no matter how rapidly or slightly, each motion is felt as an electric pulse in the magnet at the other end. To borrow a metaphor from life, it is as if the close approach and quick oscillation of the piece of soft iron fretted or tantalized the magnet, and sent a series of electrical shudders through the iron nerve.