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

speaks of a hard, violet, or deep-red colored stone, which, when heated in the sun, and then rubbed with the fingers, would attract small light bodies. We now know that when a piece of amber, wax, or glass is rubbed with a dry cloth or fur, it acquires the property of attracting light bodies, as pith balls, or bits of paper, because the friction has decomposed the natural electricity of the amber, or wax, so that it has become " minus," as Dr. Franklin would say, or resinous and negative, as it is now more famil- iarly termed ; i. e., the negative electricity is thus accumulated in a state of rest in the rubbed, non-conducting body ; so that if now it is approached by any light body, a law of electricity is observed, and the bit of paper, for instance, is attracted to the amber, and that neutralizes a given portion of its single elec- tricity, but still adheres to it. If the paper were larger, so as to neutralize all the negative electricity of the amber, it would then instantly leave by repulsion. This kind is therefore termed "frictional electricity." A quiet and simple elevation of temperature, is also alone suffi- cient to render a body electrical which was not so before. This is termed heat, or thermo-electricity, to distinguish it from pyro- electricity, which was discovered first in the tourmaline and then afterwards in other crystals and precious stones ; also to desig- nate it from hydro-electricity, which was a term early applied to voltaic electricity, and which is the same as galvanism. The third great source of electricity, then, is from chemical action; and this is termed dynamic or voltaic electricity, — so called after its distinguished discoverer, and also because it is in currents or motion. It is, as just said, also termed galvanism. But there are also two other important sources of electricity ; and these are magnetism, and the animal body. These will severally be considered under their respective heads ; but we must observe that there is another phase of electricity which we should notice, and that is, first, electricity at rest, as accumulated in or on a non-conductor, and hence termed " static electricity," and second, electricity in motion, as from chemical decomposition, &c, and hence termed " dynamic electricity." 2*