Cavendish was one of the most noted experimental investigators in the electrical field during the latter third of the eighteenth century. His work was remarkably accurate, considering the lack of a proper equipment for taking observations incident to operations in those days. He computed the relative conductivities of iron and water as four hundred million to unity, and found that the addition of but one part of common salt to one hundred of water increased the conductivity of the latter a hundredfold. A twenty-six-per-cent solution of salt he found to possess only seven and one quarter times the conductivity of the extremely weak one mentioned. He also established the law that the capacity of condensers (of which the previously mentioned Leyden jar is an example) varies directly as the active area, and inversely as the distance separating the conducting surfaces. It was reserved for later investigators to make the grand discoveries which relate to electrochemical dissociation, but Cavendish succeeded in accurately determining the ratio of combination of the elements of water in a method which superficially suggests the inverse of electrolytic decomposition--i. e., by inducing the combination of hydrogen and oxygen by the electric spark in the instrument known as the eudiometer. Hard on the heels of this work came news of Galvani's remarkable discovery (1790) of the fact that freshly amputated frogs' legs, on being touched along the lines of the muscles by dissimilar metals, were powerfully agitated. We can only speak of this discovery as the stumbling on to an isolated fact, for it was reserved for Volta to establish the generalization that a current is produced in the conductor joining dissimilar metals when the latter are both in contact with a suitable electrolyte (or liquid capable both of conducting electricity and of acting on one, and incidentally also sometimes both, of the metals). Meantime (Du Bois-Reymond observes), "wherever frogs were to be found, and where two different kinds of metal could be procured, everybody was anxious to see the mangled limbs of frogs brought to life in this wonderful way. Physiologists believed that at last they should realize their visions of a vital power, and physicians that no cure was impossible." Volta first discovered merely the fact of electrification by contact. He wrote to Galvani: "I don't need your frog. 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!" Nobili, nevertheless, in 1825 proved the existence of galvanic currents in muscles. Later on Volta invented the "_couronne des tasses_" (crown of cups), thus at the same time adopting the general form of cell used, with modifications, to-day, and producing the higher electromotive force, or electrical pressure, consequent on the multiplication of the cells in a series battery.