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Updated: June 13, 2025
Some four years after Arago's discovery, Sturgeon made the first "electro-magnet" by winding a soft iron core with wire through which a current of electricity was passed. This study of electro-magnets was taken up by Professor Joseph Henry, of Albany, New York, who succeeded in making magnets of enormous lifting power by winding the iron core with several coils of wire.
As already stated, he never accepted a negative answer to an experiment until he had brought to bear upon it all the force at his command. He had over and over again tried steel magnets and ordinary electro-magnets on various substances, but without detecting anything different from the ordinary attraction exhibited by a few of them. Stronger coercion, however, developed a new action.
It is evident that when we use permanent magnets or springs as directing forces in measuring instruments, we cannot count upon an absolute constancy in the indications, as the magnetism of the magnetized pieces, or the tension of the springs, modifies in time. The apparatus require to be regulated from time to time, and hence the idea of substituting electro-magnets for permanent ones.
"You see," said the Captain, "I use Bunsen's contrivances, not Ruhmkorff's. Those would not have been powerful enough. Bunsen's are fewer in number, but strong and large, which experience proves to be the best. The electricity produced passes forward, where it works, by electro-magnets of great size, on a system of levers and cog-wheels that transmit the movement to the axle of the screw.
He had made no little progress with sound, and demonstrated to Bell the methods by which German scientists had caused tuning-forks to vibrate by means of electro-magnets and had combined the tones of several tuning-forks in an effort to reproduce the sound of the human voice.
Magnetic concentration, or the separation of an ore from the waste gangue by the attraction of powerful electro-magnets, must therefore occupy a much more prominent place in the metallurgy of the future than it has in that of the past.
His forefinger indicated an ingenious, but now tangled and twisted, series of minute wires and electro-magnets in the broken wheel before us. Delicate brushes led the current into the wheel. With another blow of his axe, Craig disclosed wires running down through the leg of the table to the floor and under the carpet to buttons operated by the man who ran the game.
The minor features of the recorder have been simplified by other inventors of late; for example, magnets of steel have been substituted for the electro-magnets which influence the swinging coil; and the ink, instead of being electrified by the mouse-mill, is shed on the paper by a rapid vibration of the siphon point.
Platinum is nonmagnetic. It is simply a soft iron hollow ball, plated with platinum. Whichever set of electro-magnets is energised attracts the ball and by this simple method it is in the power of the operator to let the ball go to red or black as he may wish. Other similar arrangements control the odd or even, and other combinations from other push buttons.
The instrument of Gray, which is the most successful, works by intermittent currents or electrical impulses, that excite electro-magnets and move the stylus at the far end of the line. They are too complicated for description here, and are not of much practical importance.
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