FARADISM.
The Faradaic Current.
The Faradaic, induced, interrupted, or electro-magnetic current, is the third form of electricity employed in medicine. Faraday, as you will recollect, discovered, that if two metallic wires were so fixed as to be parallel and close to each other, but not to touch; and that if then a current of Voltaic electricity were sent along the first wire, another current appeared in the second. This secondary or induced current, as it is called in contradistinction to the current, the primary or inducing current sent along the first wire is only momentary, but it appears again for a moment when the first current ceases, but in a reverse direction. It is most convenient to wind these two wires round two reels, so as to form separate coils, and to place the primary within the secondary coil. Each single turn of the primary then acts not only on the parallel turn of the secondary wire, but on all the turns near it, and the power of such an apparatus is much greater than that which would be obtained by the same lengths of wire running side by side in a straight line. Our two coils being thus arranged, we pass through our primary wire a succession of electrical currents, and in practice this is accomplished by connecting its extremities with a battery supplying a continuous current, which by an ingenious mechanism we frequently break or interrupt.
Fig. 10. Faradaic Battery.
A. Cells shown by the removal of the compartment.
B. For conductors and accessories.
D. Screw regulating the pressure of a spring which modifies the vibration of the hammer, E.
E. Hammer vibrating between the electro-magnet, F, and the point of a platinized needle regulated by the screw, G.
F. Bundle of iron wires rendered an electro-magnet by the passage of the Voltaic current from the cells, A, through the primary coil, K, within which this bundle of wires is inserted.