Electricity in its relations to practical medicine / by Moritz Meyer.

  • Meyer, Moritz, 1821-1893.
Date:
1874, ©1869
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Licence: Public Domain Mark

Credit: Electricity in its relations to practical medicine / by Moritz Meyer. Source: Wellcome Collection.

Provider: This material has been provided by the Harvey Cushing/John Hay Whitney Medical Library at Yale University, through the Medical Heritage Library. The original may be consulted at the Harvey Cushing/John Hay Whitney Medical Library at Yale University.

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    pi unary current. When these windings run near one another, their action is inductive, and they produce what is called the extra current. That this is really so, may be easily seen if we take a simple galvanic battery and close it, at first with a short, and then, for comparison, with a long spirally-wound wire. In the first case we will observe a very weak, in the second a much stronger emission of sparks. From the extra current—which was also known to Faraday, but for a thorough acquaintance with which we are, however, indebted to Dove'—originates also an induced current. It arises, as such, at the opening and closing, and takes at the closing a direction opposite to, at the opening a direction corresponding with, the primitive current. That it nevertheless, at the closing, has no effect on a body intro- duced, that is not so good a conductor, is due to the fact that the current in this case finds in the battery itself a closed metallic conductor, and consequently leaves the secondary connecting body unaffected. At the opening, on the con- trary, the action is decided, because here the primary cur- rent is interrupted, and consequently the extra current flows through the body that has been introduced in its full inten- sity. A considerable increase of the extra current will be noticed if we put into the hollow of the wooden cylinder a piece of iron, or better, a split iron cylinder, or better still, a bundle of varnished wire. (Bachhoffner and Sturgeon, in Annals of Electricity, vol. i., p. 481.)' 1 Poggendorf's Annalen, Band lvi., Pag. 251. s The cause of these phenomena, it was formerly thought, lay in the fact that the metal of which wire is made is softer than a piece of ordinary iron, and consequently susceptible of greater magnetism. Magnus ( Poggendorf's Annalen, vol. xlviii., p. 95) corrected this error. He showed, by the deviation of the magnetic needle, that the bundle of wire was not more strongly mag- netized than the piece of iron by the current. He found, moreover, that the physiological action of a bundle of wire was stronger, and was still further strengthened by covering some pieces of the wire with varnish. Magnus's ex- planation was the following: The current surrounding the iron generates in the iron, at the moment it arises, a counter electric current; during its continuance Ihe iron is maintained in a state of magnetic polarization; when it stops, a current