Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.
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If we want to avoid the incessant change in these currents, and to operate rather with a succession of currents all guided in the same direction, we must have recourse to the magneto-elec- tric machine, as this has, or can have, an arrangement for that purpose ; while the automatic action of the battery induction ivill not allow of any such provisional arrangement. We observe, then, that Galvanic currents differ from Fara- daic currents in the following respects : — First. The former are continuous and in one direction ; the latter are always in interruptions, and these in rapid alternate directions ; but as the terminal shock is stronger than the initial shock, so, when taken together, they make a stronger current in that direction; and hence we nominally call one positive, and the other negative, although in fact and effect, to a degree, they are both alternately positive and negative, only one electrode is stronger than the other. Second. When the decomposition of water is brought about by the galvanic current, the hydrogen appears invariably at the negative and the oxygen at the positive pole. But if we decom- pose water by Faradaic currents, this is not the case, as each pole is alternate/// serving first for the positive and then for the negative pole, in rapid alternations, so that both hydrogen and oxygen appear at both poles. If these induction currents suc- ceed each other very rapidly, it may even happen that both gases appear simultaneously at either pole, and, both being in a nascent state, they combine again so rapidly to form water that the re- sult is as if the water was apparently not at all decomposed by these induced currents. Third. Another evidence that the Galvanic current and Far- adaic current are not alike, is, by bringing a solution of the iodide of potassium and starch into the circuit of each ; for then the blue color that indicates the liberation of iodine will shortly but moderately appear at both of the poles of Faradaic currents; while by the Galvanic current we notice the blue color quickly, and only at the positive pole.