The electric power, observed by the ancients only in amber, and perhaps the tourmaline, was in process of time found to be in glass, rosin, silk, and several other substances. By degrees it was discovered, that very strong signs of electricity were exhibited by a number of animals. The experiment of producing sparks of electrical fire, by rubbing the back of a cat in frosty weather, proved that electricity might exist in a very active state in the bodies of animals, without injuring their functions. From animals of an inferior kind a transition was made to the human species. Some people were observed to have a remarkably bright lustre of their eyes, others were found to be so strongly electrified naturally, that a very sensible electrometer was perceptibly affected, when brought near them.—Others, it is affirmed, were found so sensible to the presence of electricity, as to be affected by a flash of lightning, though so distant that the thunder could not be heard. But what principally claims our attention in regard to this part of our subject is, that there are unquestionably certain animals which can at pleasure give an electric shock, of sufficient force to kill other small animals, and that in fact they often do it. We shall describe only three of the most remarkable of these electric animals—the Gymnotus electricus, the Torpedo, and the Silurus electricus. The Gymnotus is a genus of fishes, belonging to the order of apodes. They have two tentacula at the upper lip; the eyes are covered with the common skin.—There are five rays in the membrane of the gills; the body is compressed, and carinated on the belly with a fin. There are five species; the most remarkable is the _electricus_, commonly called the _electric eel_. This species is peculiar to the Surrinam river, and they inhabit the most rocky parts of it, at a considerable distance from the sea.—The most accurate description of this fish, is in the Philosophical Transactions, for 1775, where Alexander Garden M. D. gives an account of three of them brought to Charleston in South Carolina. The largest was about three feet eight inches long, and from ten to fourteen inches in circumference, about the thickest part of the body. The head was large, broad, flat, and smooth, impressed here and there with holes, as if perforated with a blunt needle, especially towards the sides, where they are more regular. There are two nostrils on each side; one is large, tubular, and elevated above the surface; the other small and level with the skin. The mouth is large, but the jaws have no teeth, so that the animal lives by suction, or by swallowing its food entire.