In 1790, while Galvani, Professor of Anatomy in Bologna, was making experiments on electricity, he was surprised to see convulsive motions in the limbs of a dead frog accidentally lying near the machine during an electrical discharge. Though a similar action had been noticed long before his time, he was so much struck with this singular phenomenon, that he examined all the circumstances carefully, and at length found that convulsions take place when the nerve and muscle of a frog are connected by a metallic conductor. This excited the attention of all Europe; and it was not long before Volta, Professor at Pavia, showed that the mere contact of different bodies is sufficient to disturb electrical equilibrium, and that a current of electricity flows in one direction through a circuit of three conducting substances. From this he was led, by acute reasoning and experiment, to the construction of the Voltaic pile, which, in its early form, consisted of alternate discs of zinc and copper, separated by pieces of wet cloth, the extremities being connected by wires. This simple apparatus, perhaps the most wonderful instrument that has been invented by the ingenuity of man, by divesting electricity of its sudden and uncontrollable violence, and giving in a continued stream a greater quantity at a diminished intensity, has exhibited that force under a new and manageable form, possessing powers the most astonishing and unexpected. The expression current has no relation to a fluid, which is now considered to be as inconsistent with the phenomena of dynamic as with static electricity. It was shown by Grotthus that the transmission of Voltaic electricity through liquids consists of a series of chemical affinities acting in definite directions; and Mr. Grove, from an examination of its action on the various kinds of matter, has come to the same conclusion. Indeed it is now the generally received opinion that a current of electricity is merely a continuous transmission of chemical affinity from particle to particle of the substance through which it is passing, and consequently that it is a continuous transmission of force. As the Voltaic battery has become one of the most important engines of physical research, some account of its present condition may not be out of place.