the chemist, to whom it did not appear to offer one single point of interest, has derived from it a new and important instrument of research, which has already, under the guidance of Davy, multiplied discoveries with such rapidity, and to such an extent, that it is impossible to anticipate the limits of its power. Here, then, is another striking instance of a great effect produced by means apparently insignificant. Who could have imagined it possible that the spasmodic action ¦ produced in the limb of a frog, by the accidental contact of a pair of scissors, should have been the means of changing the whole system of chemistry, ― of discovering substances whose very existence was never suspected, — of elucidating the theory 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 results of science. A discovery which may appear incapable of application to-day, may be our glory tomorrow, and even 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 unerrring path to his native shores ! It has been well said by the accomplished author of Lettres à Sophie : "L'histoire des grand effets par les petits causes ferait un livre bien curieux."

The first memoir presented to the Royal Society by Mr. Davy, was read on the 18th of June 1801; and is entitled, "An Account of some Galvanic Combinations, formed by the Arrangement of Single Metallic Plates and Fluids, analogous to the new Galvanic Apparatus of Volta; by Mr. Humphry Davy, Lecturer on Chemistry in the Royal Institution; communicated by Benjamin, Count of Rumford, V.P.R.S." In order to appreciate the value of this paper, it must be remem

bered, that the agencies of two metals in exciting Galvanic phenomena were at that time supposed to be directly connected with the different powers of such metals to conduct electricity. Davy was the first philosopher who corrected this error, and, in the paper before us, showed that the evolution of galvanic energy was connected with chemical action; an inference which he deduced from some experiments, by which he found that an accumulation of Galvanic influence (exactly similar to that in the common pile, where two metals are used) might be produced by the arrangement of single metals, with different strata of fluids. This theory he established by a great variety of experiments, and showed that the alternation of two metals with fluids was no further necessary to the production of accumulated galvanic influence, than as it furnished two conducting surfaces of different degrees of oxidability; and that this production would take place, if single metallic plates were connected together by different fluids, in such a manner that one of their surfaces only should undergo oxidation, the arrangement being regular. He moreover ascertained that many of these arrangements could be made active, not only when oxidation, but likewise when other chemical changes were going on in some of their parts. Here, then, appeared the dawn of the electrochemical theory. The main fact stated in Davy's paper, namely, the relation between the energy of the pile and the oxidation of one of its metals by the interposed fluid, was readily admitted; but a question arose, whether the oxidation, instead of being the primary cause, might not be the effect of the electricity, set in motion by the contact of metals, endowed with different conducting powers. Upon this occasion, with an alacrity corresponding with the importance of the subject, Dr. Wollaston appeared in the arena, and at the meeting succeeding that at which Davy's paper was read, related to the society a series of experiments, which fully confirmed the views of Davy, and set the question for ever at rest. This fact illustrates some of the most prominent features in the scientific character of Wollaston, the quickness of his perception, the solidity of his judgment, and, above

all, the liberality and candour with which he lent his powerful aid for the promotion and advantage of a rival philosopher.

An interval of nearly five years now elapsed before Davy threw any further light upon this branch of science; but his energies had not slumbered; he had been engaged in experiments of the most arduous and complicated description; and in presenting their results, he unfolded the mysteries of Voltaic action, and, as far as its theory goes, might almost be said to have perfected our knowledge of the Galvanic pile. This grand display of scientific light burst upon Europe like a meteor, throwing its radiance into the darkest recesses, and opening to the view of the philosopher new and unexpected regions. The memoir in which these discoveries were announced constituted the Bakerian lecture; and was read before the Royal Society on the 20th November 1806. We shall endeavour to offer as popular a review of its contents as the abstruse nature of the subject will allow. It had been observed, during some of the earliest chemical experiments with the Voltaic pile, that when the purest water was submitted to the action of a current of electricity, acid and alkaline matter was separated at the opposite electrified surfaces. A fact so extraordinary necessarily excited various conjectures; and many believed that the bodies were actually generated by the action of the pile. Davy, however, soon negatived so unphilosophical a conclusion, and showed that they merely arose from the decomposition of the materials employed: he found, for instance, that the glass vessel, at its point of contact with the wire, was corroded; a fact which sufficiently explained the source of the alkali; while the animal or vegetable materials, employed as conductors, might be readily supposed to furnish the acid. He accordingly proceeded to work with cups of agate; and, at the suggestion of Dr. Wollaston, who again acted as a Mentor, he formed the connecting parts of well-washed asbestos. Thus then was every source of fallacy connected with the apparatus removed; but still the same production of saline matter appeared. What could be its origin? He repeated the ex

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periments in cups of gold, and examined the purity of his water by evaporation in vessels of silver. At length he succeeded in recognising the source of this matter: it was of foreign origin, partly derived from the contents of the water, and partly from new combinations of gaseous matter. was curious, but, after all, a discovery in itself of insignificant value, when compared with those which immediately flowed from it. The acid and alkaline matter then produced, it has been already stated, collected in the water round opposite poles; the former always appearing at the positively electrified, the latter at the negatively electrified surface. Was this a universal law? It was necessary to decide this question by more extended enquiries. The first series of experiments which he instituted for this purpose, embraced the decomposition of solid bodies, insoluble, or difficultly soluble in water. From the effects of the electrical agency on glass, already mentioned, he very reasonably expected that various earthy compounds might thus undergo changes under similar circumstances; and his conclusion was just. From sulphate of lime he obtained sulphuric acid in the positive, and a solution of lime in the negative cup. These experiments were extended to a great variety of other compounds, such as sulphate of strontia, fluate of lime, sulphate of baryta, &c., and with parallel results. Having thus far established the general law, he proceeded to enquire into the mode and circumstances under which these constituent parts were transferred to their respective poles; and he discovered, first, that acid and alkaline bodies, during the time of their electrical transfer, would pass through water containing vegetable colours, without affecting them, or combining with them; and, secondly, that such bodies would even pass through chemical menstrua having stronger attractions for them, thereby showing that the same power which destroyed elective affinity in the vicinity of the metallic points, would likewise destroy or suspend its operation, throughout the whole of its circuit. Thus, proceeding step by step, with philosophic caution and unwearied perseverance, did he develope all the particular phænomena and

details of his subject; his genius then took flight, and with an eagle's eye caught the plan of the whole. A new science was created; and so important and extensive were the applications of its principles in producing chemical composition and decomposition, that it justly derived the name of ElectroChemistry. Its illustrious author, reasoning upon the phænomena it displayed, arrived at the plausible conclusion, that the power of electrical attraction and repulsion must be identical with chemical affinity. If this be true, we at once obtain a solution of the problem, and can explain the action of the electric fluid in disuniting the elements of chemical combinations; for it is evident, that if two bodies be held together by virtue of their electrical states, by changing their electricity we shall disunite them. In this view of the subject, every substance, it is supposed, has its own inherent electricity, some being positive, others negative. When, therefore, bodies in such opposite states are presented to each other, they will combine.

The fame of Davy, as a philosopher, may, with perfect confidence, be rested upon this single memoir. It is true that the discoveries immediately resulting from the application of the principles therein contained are more dazzling to ordinary minds, but in our judgment they are far less glorious. Does not Sir Isaac Newton deserve greater fame for his invention of Fluxions than for the calculations performed by the application of them? We do not hesitate in comparing these great philosophers, since each has enlightened us with discoveries alike effected by means of his own creation. Not only did both unlock the choicest casket of nature, but they had the superior merit of planning and constructing the key.

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In a conversation between Sir Humphry Davy and a scientific friend, the former observed that a philosopher might always discover how posterity would appreciate his labours, from the opinion entertained of them by contemporary reigners; who, being unbiassed by circumstances of personality or rivalry, will reduce every object to its just proportions and proper value. If such a standard be acknowledged,