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

Nature of Electricity. It is important, before we go further, for us to form an idea of the properties of electricity, or, in other words, of what electricity is; at least, to be reminded of the opinions that have been formed on this subject. The knowledge of these theories, as has been remarked, is absolutely necessary for us, even were it only to make us familiar with the established expressions em- ployed by writers on this subject. But all this will be more fully and naturally explained, in connection with the history of the development of this branch of science. Here then, we will only stop to mention certain prominent opinions. Dr. Benjamin Franklin's theory consisted in admitting but one single imponderable electric fluid, very subtile, and that all the particles of which mutually repel each other; that each body has a determinate capacity for this fluid ; that a body is in a natural electric state when it contains as much as it ought naturally to have. He held that to electrize a body vitreously, is to give it more electricity than it naturally contains; and when so conditioned, the body is in the positive electric state. To electrize a body resinously, is simply to deprive that body of a portion of its natural electricity, and then it is in a negative electric state. So that Franklin's theory gave rise to the terms positive and negative electricity the world over. But his the- ory of simple plus and minus, just as he gave it, cannot, in the present state of the sciences, be admitted. We now regard the two electricities, the vitreous and the i-esinous, as excessively subtile and imponderable fluids or influences, each of which orders is composed of particles that naturally repel each other, while the particles of the one order as naturally attract those of the other order; that these differ- ent influences or fluids are able to travel in and through con- ducting bodies ; yet as their fellow-particles of the given order tend to repel each other mutually, they therefore, when on insulating bodies, arrange themselves on the surface of these, and remain, because they meet the dry air, which being to them an insulator, they can go no farther. Why a given article, as amber or glass,