Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.
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Magneto-Electricity. Magneto-electricity is a term used to designate certain induc- tion currents from other induction currents called electro-mag- netic,— these latter being produced by the electro-magnetic machine, while the former are produced, on the contrary, by per- manent magnets which are called magneto-electric machines. This, too, was the result of Dr. Faraday's profound researches. He found that if the poles of an ordinary horseshoe magnet be approached by one of the ends of a copper wire, that is thoroughly insulated and wound like a helix around a wooden spool, then the needle of the galvanometer which is in the cir- cuit is immediately deflected, but that the needle soon comes again to rest. This, he observed, was repeated also when the end of the wire was removed from the pole of the magnet, and that in the opposite direction; and then again the needle soon came to rest. This indicated that an instantaneous current of a given direction is produced when the wire of the helix approaches the pole of the magnet, — and that this is repeated, but in the opposite direction, when the wire is receding from the magnet. For producing a succession of shocks, so as to make up a cur- rent, the magnet, or else the wire, must be regularly approached and withdrawn in quick succession. To bring this about in the most effective and practical manner, there is hung upon a shaft a soft iron armature, that is wound on both arms with a long coil of copper wire for induction, and this is set in revolving motion near the poles of a large and fixed permanent magnet by means of crank, wheels and gearing. This is kept in lively motion by some person turning the wheel, the which turns the armatures some eight times around to its once, and the armatures thus passing the poles of the magnet twice to every turn of it, makes some sixteen shocks to every turn of the crank. Every time the armature coils approach and pass the poles of the great compound permanent magnet, the soft iron armature is mag- netized and demagnetized, and thus two momentary currents of electricity are educed, — the one at the instant of approaching