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

have shown, by the increase of number in the pairs that com- pose the compound battery, but without an increase of size. We conclude, then, that a galvanic current is great in quan- tity, and capable for chemical action, if produced by a single pair or more, much in proportion to the size and action of the pair if connected with a thick wire. The density, tension, and intensity of the current for passing over and through poor con- ductors will be much in proportion to the number of the series, and the smaller size of the wire connections and conductors. The efficiency of every battery depends upon good contacts. This is mentioned particularly, because the greatest and most frequent failures, partial failures, or differences of results, arise from this want of exact care. There is another method for increasing the electro-motive force of even a small galvanic current of a single pair, as well as some modified kind of intensity; but this must be reserved for the next chapter. Derived currents, spoken of by authors, are those that are obtained by a sort of by-path, namely, when the conductor of a closed circuit is conveying a galvanic current, this is termed the primary current. If, now, we add a short and nearly parallel conductor by making contact at its metallic ends, on the route of the primitive wire, a portion of the current will pass along the second wire, provided it is not much longer nor smaller, nor otherwise a poorer conductor, than the primary wire. And this is termed a derived current. The author, however, finds no use for such in therapeutics. Electric Heat. Heat can be produced by an obstructed or retarded current of electricity, as, for instance, where a large quantity current is led by a wire too small to convey it all freely, or through a poor conductor, as platinum. It may be evolved by the disruptive discharge between the two poles of a galvanic battery, where disintegration is effected, and the particles of one pole pass over to the other pole, with the evolution of intense heat and light.