This was at first a difficulty apparently impossible to remove. It was so self-evident that the discs of metal, if placed in a pile in a series of pairs, would continually exercise like effects to the first pair of discs, that Volta was puzzled, and for some time he could not arrive at any reasonable solution. At last it struck him that if he placed between the discs some slow-conducting substance, the electricity would not pass from disc to disc, and the force developed or set in motion would be more powerful.
He made the experiment. The result was the Voltaic pile made in 1800, of which we give an illustration (fig. 219). A communication on the subject of Electricity by contact, written by M. Volta, is to be found in the _Philosophical Proceedings_ for the year 1800.
Volta constructed the pile which bears his name, on the assumption that “every two heterogeneous bodies form a galvanic circle or arc in which electricity is generated.” The “pile” consisted of a number of discs of zinc and copper separated by discs of card soaked in water. This combination of metals separated by a bad conductor, developed considerable electricity, the “positive” going to the zinc at the top, and the “negative” turning to the opposite end. By touching the zinc and copper extremities simultaneously with wetted fingers we shall experience a shock. “I don’t need your frog,” Volta said, when he had proved his theory; “give me two metals and a moist rag, and I will produce your animal electricity. Your frog is nothing but a moist conductor, and in this respect it is inferior to my wet rag!”
After this discovery the theory of animal electricity died away for many years, till in 1825, Nobili, and afterwards Matteucci, proved the existence of galvanic currents in muscles.
After Volta had succeeded in obtaining a shock from his “pile,” he proceeded to the construction of another instrument, or rather apparatus, which he denominated “Couronne des tasses” (fig. 220). It consisted of a series of small glasses containing water or a saline solution. He then procured a number of “metallic arcs,” partly composed of zinc and partly of copper; these were inserted into the glasses, so that every glass contained the zinc of one and the copper of another arc, not in contact, but one at the right hand the other at the left. The electro motion, supposed to be the primary cause of the galvanic action, was thus produced as well as from the “pile.” The principle was just the same in both apparatus, the metals being divided by the water in one case, and by a wet card or cloth in the other.