Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.

power, and therefore the globe will always have some degree of effect upon the static needle. Yet it is certainly proved that the electric current does, more promptly and completely, control a needle so prepared as to be double and reversed than the single magnetized needle. If the conducting wire of the galvanic current is placed hor- izontally below the needle so as to run north, the north pole of the needle is instantly deviated eastward. If the electric cur- rent is now reversed so as to run southward, the north pole of the needle flies to the west. But if now the conducting wire is raised above the needle, and still horizontal, the deviations of the needle always occur in the contrary direction. While M. Ampere took up M. Oersted's discovery to generalize and extend it, M. Arago was looking into this matter, and soon showed that an electric current not only acts upon a magnetized needle, but that it also acts upon all magnetizable bodies, even when they are not magnetized. Having coiled a small, soft iron wire, he found that when this wire was being traversed by a strong electric current, it acquired the property of attracting and retaining around it a certain quantity of iron filings, much like a cylindrical envelope, but that the instant the current ceased to pass the filings fell off; but as soon as the current run again, the wire took them up again. M. Arago further showed that the powerful charge of a Ley- den jar even, may magnetize a steel needle, if placed in the in- terior of a helix made of metal wire through which this dis- charge is made to pass. Sir H. Davy soon afterwards discovered that we can magnetize common sewing needles by merely rubbing them back and forth transversely over a rectilinear wire while it is being traversed by the electric current of a battery. These experiments prove that the electric current impresses upon bat- tery conductors, that are thus traversed, properties perfectly like those of magnets, not only those of magnetic bodies: but in fact it actually magnetizes those thus traversed. M. Ampere found, besides, that a galvanic current not only acts upon a magnet, but that it also exercises an action upon another contiguous electric current, which may be stated thus :