Volta, his contemporary and countryman, finally solved the problem as to the reason why. and made that "Voltaic Pile" which came to be our modern "battery." Acting upon the hint given by Galvani's accident, this pile was made of thin sheets of metal, say of copper and zinc, laid in series one above the other, with a piece of cloth wet with dilute acid interposed between each sheet and the next. The sheets were connected at the edges in pairs, a sheet of zinc to a sheet of copper, and the pile began with a sheet of one metal and ended with one of the other. It is to be noted that a single pair would have produced the same result as a hundred pairs, only more feebly. A single large pair is, indeed, the modern electric battery of one cell. The beginning and the ending sheets of the Voltaic pile were connected by a wire, through which the current passed. We, in our commonest industrial battery, use the two pieces of metal with the fluid between. The metals are usually copper and zinc, and the fluid is water in which is dissolved sulphate of copper. The wire connection we make hundreds of miles long, and over this wire passes the current. If we part this wire the current ceases. If we join it again we instantly renew it. There are many forms of this battery. The two metals, the _electrodes_, are not necessarily zinc and copper and no others. The acidulated fluid is not invariably water with sulphate of copper dissolved in it. Yet in all modifications the same thing is done in essentially the same way, and the Voltaic pile, and a little back of that Galvani's frog, is the secret of the telegraph, the telephone, the telautograph, the cable message. In the case of Galvani's frog, the fluids of the recently killed body furnished the liquid containing the acid, the copper hook and the iron railing furnished the dissimilar metals, and the nerves and muscles of the frog's body, connecting the two metals, furnished the wire. They were as good as Franklin's wet string was. The effect of the passage of a current of electricity through a muscle is to cause it to spasmodically contract, as everyone knows who has held the metallic handles of an ordinary small battery. Many years passed before the mystery that has long been plain was solved by acute minds. Galvani thought he saw the electric quality _in the tissues of the_ frog. Volta came to see them as produced _by chemical action upon two dissimilar metals_. The first could not maintain his theories against facts that became apparent in the course of the investigations of several years, yet he asserted them with all the pertinacious conservatism of his profession, which it has required ages to wear away, and died poor and unhonored. The other became a nobleman and a senator, and wore medals and honors. It is a world in which success alone is seen, and in which it may be truthfully said that the contortions of an eviscerated and unconscious frog upon a