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

satisfactorily for them. M. De la Rive compares them to the deviations of the galvanometer, under like circumstances. For instance, while Faraday was making experiments to determine the velocity of galvanic electricity, he obtained the use of several hundred coils of large telegraph wire, covered with gutta percha, and intended for subterranean or submarine lines, which were half a mile in length each. He suspended these to a series of barges, in a canal, so that each coil was plunged entirely under water its whole length, with the exception of a very short bit at each end. These he connected metallically end to end, so as to constitute a single wire of some two hundred miles in length. Then he attached to one end of this long, insulated wire a com- pound galvanic battery composed of three hundred and sixty cups, and hence as many pairs of zinc and copper plates, in acidulated water, including in the circuit also a very sensitive galvanometer. Then, after the current had thus been traversing this long wire for a time, at the moment when communication was cut off between the battery and the long wire, a very strong shock was felt, by merely touching for an instant either end of the long wire. This he found could be repeated some forty times in succession, with the same residt, but less and less in degree. Again: instead of thus touching the long wire and so leading off the accumulated electricity so immediately after taking away the battery from it, if one pole or end is placed in connection with the galvanometer, while the other end or pole connects witli the ground, then the needle of the instrument was quickly and powerfully deflected; and this was still sensible, if the trial was not made again with it, for some half hour. Faraday explains this as the result of the thus formed unique Leyden jar of enormous length; consisting of the long wire, the envelope by which it was insulated, and the liquid which surrounded it. The wire plays the inner coat of the Leyden jar, which is charged. The gutta percha, being a non-conductor, is the jar itself; while the water, or the moist earth, is the con- ductor for its negative electricity, like the outside of a positively charged Leyden jar. Volta early showed that a Leyden jar might be charged by connecting its inner coating of foil with