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

of less relative tension,) will produce only the least spark. Now, if these two kinds of electricities, i. e., positive and nega- tive, be constantly renewed, there will likewise be a continuous neutralization, either through the air as a fine succession of sparks, or through a conductor in contact. The essential dif- ference between a discharge of electricity, and a current of elec- tricity, as they relate to physiology and therapeutics, will be plainly delineated in this work. I will only mention here, that a discharge or shock, although it produces a number of other powerful effects, has almost no chemical effect and no influence on the magnetic needle, whilst all currents of electricity are able to accomplish both. We find that we can produce electricity instantly and con- stantly; but the accumulation of electricity is a matter of time. And here I must remind you of an electric law that is not so known, or else is more generally forgotten ; and that is, that one of the electricities by friction is never liberated without the other or opposite electricity being equally so, and that in the same proportion. 1 mention this as a particular reminder, be- cause a provision must for this reason be always made for the escape (as for instance to the earth) of the electricity we do not want, in order to obtain freely and largely that other kind which we do want. This law, first laid down by M. Wilke, ap- plies also to other forms of electricity, but all the more distinc- tively in this, where one only of the electricities is collected, as for instance when highly charging the Leyden jars. True, Faraday caused two bands of flannel to be rubbed against each other crosswise, and thus both were rendered negative. But this is an apparent exception, although it can be explained. Finally, we are taught that the kind of electricity that is de- veloped upon a body does not depend solely upon the nature of this body, but likewise upon that of the substance with which it is acted upon, or rubbed, as one electricity is never developed without its opposite; and either of these may prefer to accumu- late on the one or other body. There is not, therefore, an iden- tity between the electricity that glass acquires by friction, and which we call vitreous, and that which wax acquires, and which