Clinical manual for the study of medical cases / edited by James Finlayson.

Date:
1878
Catalogue details

Licence: Public Domain Mark

Credit: Clinical manual for the study of medical cases / edited by James Finlayson. Source: Wellcome Collection.

    238/616 (page 210)
    secondary coil is arranged outside of the first, and can be moved over it towards the central magnet or away from it. Currents are induced again in this outer coil in opposite directions to those in the inner. In the second form of Faradic electricity (Magneto-Electric instruments), two coils are arranged, in the form of little bobbins which by some mechanical arrangement (such as the turning of a handle) are brought alternately and in rapid succession in front of the two poles of a horse-shoe magnet. There are pieces of soft iron within these bobbin-like coils, and these are magnet- ised and demagnetised according as they are approximated to or removed from the poles of the magnet: currents similar to those described in the preceding paragraph are developed at each act of magnetising and demagnetising. Both of these forms (electro-magnetic and magneto-electric) are to be regarded, for most medical purposes at least, as essen- tially similar; they are both spoken of as Faradic, induced, and interrupted currents. These currents are instantaneous and pass alternately in opposite directions; the rapidity of their succession may be judged of by the number of clicks heard during the action of the machine, as these vary with the inter- ruptions. Arrangements are usually provided for obtaining rapidly or slowly interrupted currents by springs and screws in the one form, and by varying the rate of rotation in the other. The currents from the inner and outer coils are employed separ- ately, the former yielding the primary induced current, and the latter the secondary induced current. This primary induced current (the extra current of physicists) must not be confounded with the primary current from a galvanic battery; the intervention of a coil shows that we have to deal with an induced current. Some forms of apparatus allow of the use of these induced currents always in the same direction, the reverse currents being unused. A third form of electricity (the static) may be named the Fkanklinic : it is produced by friction : glass plates or cylinders are rotated against cushions, and a patient placed on an insulated