It cannot be expected that I should enter into a minute history of the science; such a labour would require a distinct work for its accomplishment. I shall therefore follow the plan of the architect, who, in presenting a finished drawing of a part, sketches a faint outline of the whole edifice to which it belongs, in order that its fair proportions may appear in proper breadth and relief. The FIRST EPOCH may be considered as arising out of the fundamental fact discovered by Galvani in 1790--that the contact of two different metals with the nerve of a recently killed frog will excite distinct muscular contractions. THE SECOND EPOCH may be dated from the discovery of what might be termed _Organic_ Galvanism, or the production of its influence, without the presence of animal organs, by the peculiar action of metals upon water, as first observed by Dr. Ash. THE THIRD EPOCH will long be celebrated on account of the discovery of the accumulation of the Galvanic power, by the invention of the pile of Volta, made known in the first year of the present century, and which so distinctly exhibited the analogy between Galvanism and Electricity, that the energy thus excited is now generally spoken of as "_Voltaic Electricity_." THE FOURTH EPOCH may be considered as founded upon the knowledge of the general connexion between the excitement of Voltaic electricity and chemical changes. THE FIFTH EPOCH is exclusively indebted for its origin to Davy--the establishment of the general law, that Galvanism decomposes all compound bodies, and that the decomposition takes place in a certain determinate manner. THE SIXTH AND LAST EPOCH is founded upon the discovery of the relations subsisting between electricity and magnetism; giving origin to a new branch of science, which has been distinguished by the name of "ELECTRO-MAGNETISM." Galvani,[53] from the moment of his first discovery, always referred the effects he produced to an electrical origin; but he considered that the metals employed merely acted as conductors, which effected a communication between the different parts of an animal, naturally, or by some process of nature, in opposite states of electricity, and that the muscular contractions took place during the restoration of the equilibrium. [53] The simple fact relating to the action of metals on the animal organs was certainly not first observed by Galvani, but by Sulzer, who has described the sensation of taste produced by the contact of lead and silver with the tongue, in his _Théorie des Plaisirs_, in 1767. Until the researches of Dr. Ash,[54] Ritter, Fabroni, and Creve, had been made known, the Galvanic influence was generally considered as existing only in the living organs of animals, from which it might be elicited by certain processes.