has already, under the guidance of Davy, multiplied discoveries with such rapidity, and to such an extent, that it is not even possible to anticipate the limits of its power.

We have here, then, another striking instance of a great effect produced by means apparently insignificant. Who could have imagined it possible, that the spasmodic action occasioned in the limb of a frog, by the accidental contact of a pair of scissors, should have become the means of changing the whole theory of chemistry-of discovering substances, whose very existence was never suspected-of explaining the anomalous associations of mineral bodies in the veins of the earth of protecting surfaces of metal from the corrosive action of the elements-of elucidating the theories of volcanoes and earthquakes—and, may we not add, of leading the way to a knowledge of the laws of terrestrial magnetism!

Such an unexpected extension of an apparently useless fact should dispose us to entertain a kinder regard for the labours of one another, and teach us to judge with diffidence of the abstract results of science. A discovery which may appear incapable of useful application to-day, may be our glory to-morrow, it may even change the face of empires, and wield the destiny of

nations.

The conic sections of Apollonius Pergæus remained useless for two thousand years: who could have supposed that, after the lapse of twenty centuries, they would have formed the basis of astronomy?-a science giving to navigation safety, guiding the pilot through unknown seas, and tracing for him in the heavens an unerring path to his native shores.

Some apology may be necessary for this digression; but I confess the subject has always appeared to me to be capable of much interesting illustration, and I heartily concur in the opinion expressed by the accomplished author of "Lettres à Sophie"-" L'Histoire des grands effets par les petites causes ferait un livre bien curieux."

CHAPTER VI.

The History of Galvanism divided into six grand Epochs.-Davy extends the experiment of Nicholson and Carlisle.-His Pile of one metal and two fluids.-Dr. Wollaston advocates the doctrine of oxidation being the primary cause of Voltaic Phenomena.-Davy's modification of that theory. His Bakerian Lecture of 1806. He discovers the sources of the Acid and Alkaline matter eliminated from water by Voltaic action.--On the nature of Electrical decomposition and transfer.-On the relations between the Electrical energies of bodies, and their Chemical Affinities.-General developement of the Electro-chemical Laws.-Illustrations, Applications, and Conclusions.

THE History of Galvanism may be divided into six grand epochs; each being distinguished by the discovery of facts variously interesting from their novelty, and from the extent and importance of their applications.

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 “ ELECTROMAGNETISM."

Galvani,* 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.

Until the researches of Dr. Ash,† 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.

In the Bakerian Lecture‡ read before the Royal Society in 1826, Davy, in

*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.

+ M. Humboldt (Ueber die gereize Faser, l. 473, 1797,) quotes part of a letter from Dr. Ash, in which it is said that, "if two finely polished plates of homogeneous zinc be moistened and laid together, little effect follows; but if zinc and silver be tried in the same way, the whole surface of. the silver will be covered with oxidated zinc. Lead and quicksilver act as powerfully upon each other, and so do iron and copper. M. Humboldt says, that, in repeating this experiment, he saw air bubbles ascend, which he supposes to have been hydrogen gas from the decomposition of

water.

As this lecture will be frequently mentioned in the progress of these Memoirs, in connexion with most important discoveries, it may be interesting to the reader to learn something of its foundation and design. I have therefore collected the necessary information from the Minutes of the

giving a retrospective view of the progress of Electro-chemical Science, very justly remarks, that the true origin of all that has been done in this department of philosophy was the accidental discovery of Nicholson and Carlisle, of the decomposition of water by the pile of Volta, on the 30th of April, in the year 1800; which was immediately followed by that of the decomposition of certain metallic solutions, and by the observation of the separation of alkali on the negative plates of the apparatus. Mr. Cruickshank, in pursuing these experiments, obtained many new and important results, such as the decompo sition of the muriates of magnesia, soda, and ammonia; and also observed the fact that alkaline matter always appeared at the negative, and acid matter at the positive pole.*

No sooner had Davy become acquainted with the curious experiments of Nicholson and Carlisle, than, as we learn from his letter to Mr. Gilbert,† bearing the date of July 1800, he proceeded to repeat them. Indeed, it was the early habit of his mind not only to originate enquiries, but without delay to examine the novel results of other philosophers; and in numerous instances it would seem, that he only required to confirm their accuracy before he succeeded in rendering the application of them subservient to farther discovery. This was certainly the case with respect to the subject before us; he was a discoverer as soon as he became an enquirer. It is admirable to observe with what a quick quick perception he discovered the various bearings of a new fact, and with what ingenuity he appropriated it for the explanation of previously obscure phenomena. In referring to the " Additional Observations" appended to his "Chemical Researches," we shall find that the moment he became

Royal Society. Mr. Baker is well known in the history of science, as an accurate observer with the microscope, and as the author of several works on the subject. By his will, dated July 1763, he bequeathed the sum of one hundred pounds, the interest of which he directed " to be applied for an Oration or Discourse, to be read or spoken yearly by some one of the Fellows of the Royal Society, on such parts of Natural History, or Experimental Philosophy, at such time, and in such manner, as the President and Council of the said Society shall please to order and appoint; on condition, nevertheless, that if any one year shall pass after the payment of the said hundred pounds, without such oration or discourse having been read or spoken at some Meeting of the said Royal Society, the said hundred pounds shall then become forfeited, and shall be repaid by the said Society to his executors," &c. Baker died in November 1774, and in the following year a Fellow was nominated to read the lecture. It is a whimsical circumstance, that the first lecturer should have been PETER WOULFE, the last of the alchemists. The names of the successive lecturers were as follow:Dr. Ingenhouz, Mr. Cavallo, Mr. Vince, Dr. Wollaston, Dr. Young, Sir H. Davy, Mr. Brande, Captain Kater, Captain Edward Sabine, and Mr. Herschel.

Nicholson's Journal, Vol. IV. p. 190.

+ See page 58.

acquainted with the experiments of Dr. Ash, he proceeded to enquire how far the fact, previously noticed by himself, of the conversion of nitrous gas into nitrous oxide, by exposure to wetted zinc, might depend upon galvanic

action.

In the month of September 1800, he published his first paper on the subject of Galvanic Electricity, in Nicholson's Journal, which was followed by six others, in which he so far extended the original experiment of Nicholson and Carlisle, as to show that oxygen and hydrogen might be evolved from separate portions of water, though vegetable and even animal substances intervened; and conceiving that all decompositions might be polar, he electrised different compounds at the different extremities, and found that sulphur and metallic bodies appeared at the negative pole, and oxygen and azote at the positive pole, though the bodies furnishing them were separated from each other. Here was the dawn of the Electro-chemical theory.

In a letter to Mr. Gilbert, already printed in these memoirs,* he announced his opinion that Galvanism is a process principally chemical; and, in a subsequent communication to the same gentleman, written on the eve of his departure for Bristol to the Royal Institution, we discover a farther developement of the same theory, which, although modified by future researches, became, as we shall hereafter find, materially instrumental in establishing juster views of the nature of Voltaic action.

As soon as it was discovered that galvanic power might be excited by the contact of metals, without the interposition of animal organs, it was imagined that the electricity was set in motion by the contact of bodies possessing different conducting powers, without any reference to the chemical action which accompanied the process. This theory was naturally suggested by the fact discovered by Mr. Bennett several years before-that electricity is excited by the mere contact of different metals: thus, when a plate of copper and another of zinc, each furnished with an insulating glass handle, are made to touch by their flat surfaces, the zinc, after separation, exhibits positive, and the copper negative electricity. In this case, it is fair to conclude that a certain quantity of electricity had moved from the copper to the zinc.

On trying other metals, Volta found that similar phenomena arose; from which property such bodies have been denominated "motors" of electricity, and the process which takes place electro-motion, terms which have since been sanctioned and adopted by Davy.