instant, "a capital experiment." This discovery was soon followed by that of the decomposition of soda; and shortly after, of other bodies of the same kind; and the interest and activity of the whole chemical world were turned to the subject in an intense degree.

At this period, there might be noticed three great branches of speculation on this subject; the theory of the pile, the theory of electrical decomposition, and the theory of the identity of chemical and electrical forces; which last doctrine, however, was found to include the other two, as might have been anticipated from the time of its first suggestion.

It will not be necessary to say much on the theories of the voltaic pile, as separate from other parts of the subject. The contact-theory, which ascribed the action to the contact of different metals, was maintained by Volta himself; but gradually disappeared, as it was proved (by Wollaston especially,) that the effect of the pile was inseparably connected with oxidation or other chemical changes. The theories of electro-chemical decomposition were numerous, and especially after the promulgation of Davy's Memoir in 1806; and, whatever might be the defects under which these speculations for a long time labored, the subject was powerfully urged on in the direction in which truth lay, by Davy's discoveries and views. That there remained something still to be done, in order to give full evidence and consistency to the theory, appears from this;—that some of the most important parts of Davy's results struck his followers as extraordinary paradoxes; -for instance, the fact that the decomposed elements are transferred from one part of the circuit to another, in a form which escapes the cognizance of our senses, through intervening substances for which they have a strong affinity. It was found afterwards that the circumstance which appeared to make the process so wonderful, was, in fact, the condition of its going on at all. Davy's expressions often seem to indicate the most exact notions: for instance, he says, "It is very natural to suppose that the repellent and attractive energies are communicated from one particle to another of the same kind, so as to establish a conducting chain in the fluid; and that the locomotion takes place in consequence;" and yet at other times he speaks of the element as attracted and repelled by the metallic surfaces which form the poles ;a different, and, as it appeared afterwards, an untenable view. Mr. Faraday, who supplied what was wanting, justly notices this vagueness.

Phil. Trans. 1801, p. 427.

7 Paris, i. 154.

BETAVILI CĂ EVA mus hoang of 1906, otherwise than is a great men Jerlies the Des myrat erret of the epoch now THE TAEV. And as spa T vs Tanglized a core all over Europe. I parmelad I made De LSI-ushed bone tể being crowned by Descrm of Fries wand the party and England were de agua a ier bescing. Bonapark had proposed a prize of SITŲ DIGISLIČ Žus tu de pesa vie ly is aperiments and disrorumus skolā abrane the knovahy of decricity and galvanism, s much as Frankie and Tea bit and of three thousand franes de the best ergermenn vieh shoud be made in the ecurse of each THAT NO TE KÜTLe fait de amter pene was by the First Class of The AISCTER. Svarbed as Dury.

From this period be mise mazily to broers and distinctions, and reached a begin of socande áme s gas las ever fallen to the 324 of a diseckaner in so short & Lone. I shall not, however, dwell on soch einemmstances be refue myself to the progress of my subject.

Sect. 2—Escala shamena y the Eletro-chemical Theory by Faraday.

THE Sefects of Dary's theoretical views will be seen most clearly by explaining what Faraday abled to them Michael Faraday was in every way fined and led to become Pary's successor in his great career of discovery. In 1812, being then a bookseller's apprentice, he attended the lectures of Davy, which at that period excited the highest aimination' My desire to escape from trade," Mr. Faraday says, which I thought vicious and selfish, and to enter into the service of science, which I imagined made its pursuers amiable and liberal, induced me at last to take the bold and simple step of writing to Sir H. Davy." He was favorably received, and, in the next year, became

* Researches, 482.

* Paris, ii. &

Davy's assistant at the Institution; and afterwards his successor. The Institution which produced such researches as those of these two men, may well be considered as a great school of exact and philosophical chemistry. Mr. Faraday, from the beginning of his course of inquiry, appears to have had the consciousness that he was engaged on a great connected work. His Experimental Researches, which appeared in a series of Memoirs in the Philosophical Transactions, are divided into short paragraphs, numbered into a continued order from 1 up to 1160, at the time at which I write; and destined, probably, to extend much further. These paragraphs are connected by a very rigorous method of investigation and reasoning which runs through the whole body of them. Yet this unity of purpose was not at first obvious. His first two Memoirs were upon subjects which we have already treated of (B. xiii. c. 5 and c. 8), Voltaic Induction, and the evolution of Electricity from Magnetism. His "Third Series" has also been already referred to. Its object was, as a preparatory step towards further investigation, to show the identity of voltaic and animal electricity with that of the electrical machine; and as machine electricity differs from other kinds in being successively in a state of tension and explosion, instead of a continued current, Mr. Faraday succeeded in identifying it with them, by causing the electrical discharge to pass through a bad conductor into a discharging-train of vast extent; nothing less, indeed, than the whole fabric of the metallic gas-pipes and water-pipes of London. In this Memoir" it is easy to see already traces of the general theoretical views at which he had arrived; but these are not expressly stated till his "Fifth Series ;" his intermediate Fourth Series being occupied by another subsidiary labor on the conditions of conduction. At length, however, in the Fifth Series, which was read to the Royal Society in June, 1833, he approaches the theory of electro-chemical decomposition. Most preceding theorists, and Davy amongst the number, had referred this result to attractive powers residing in the poles of the apparatus; and had even pretended to compare the intensity of this attraction at different distances from the poles. By a number of singularly beautiful and skilful experiments, Mr. Faraday shows that the phenomena can with no propriety be

December, 1835. (At present, when I am revising the second edition, September, 1846, Dr. Faraday has recently published the "Twenty-first Series" of his Researches ending with paragraph 2453.)

"Phil. Trans. 1833.

aserbed at the attraction of the poles. As the substances evolved anases of electro-chemical decomposition may be made to appear aransi ain” which, according to common language, is not a conSartor, nor is decomposed; or against water," which is a conductor, and can be decomposed; as well as against the metal poles, which are exclam ocolantes, but undecomposable: there appears but little reason to ectssler this phenomenon generally as due to the attraction or attractive powers of the latter, when used in the ordinary way, since similar surati is can hardly be imagined in the former in

Faraday's opinion, and indeed, the only way of expressing the resuls of his experiments, was that the chemical elements, in obedence to the direction of the vitale currents established in the decomposing substation, were evolved, or, as he prefers to say, ejected # :s amates". He afterwards states that the influence which is present in the decarie ezment may be described as an axis of power, kering (sa each point) contrary forces exactly equal in amount in con

Having served at this point. Faraday rightly wished to reject the term paix, and other words which eculd hardly be used without suggost, g doctrines now proved to be erroneous. He considered, in the esse of bodis electrically decomposed, or, as he termed them, electro

as the elements as travelling in two opposite directions; which, with refrence to the direction of terrestrial magnetism, might be assadored as naturally east and west; and he conceived elements as, in this way, arriving at the doors or outlets at which they finally made their separate appearance. The doors he called electrodes, and, separately, the anode and the oath de" and the elements which thus travel be termed the anion and the cation (or cathion). By means eë të a nomenclature he was able to express his general results with wack more dictarnos and facility.

Bat this general view of the electrolytical process required to be parand firebon in order to explain the nature of the action. The aderngy of electrical and chemical forces, which had been hazarded as

Researches, Arts 465, 469.

517.

17 663. **The amalner of the Greek derivation requires cation; but to make the relation to veku oễvious to the English reader, and to avoid a violation of the habits of Dinglish pronunciation, I should prefer cathion.

a conjecture by Davy, and adopted as the basis of chemistry by Berzelius, could only be established by exact measures and rigorous proofs. Faraday had, in his proof of the identity of voltaic and electric agency, attempted also to devise such a measure as should give him a comparison of their quantity; and in this way he proved that" a voltaic group of two small wires of platinum and zinc, placed near each other, and immersed in dilute acid for three seconds, yields as much electricity as the electrical battery, charged by ten turns of a large machine; and this was established both by its momentary electro-magnetic effect, and by the amount of its chemical action.20

It was in his "Seventh Series," that he finally established a principle of definite measurement of the amount of electrolytical action, and described an instrument which he termed" a volta-electrometer. In this instrument the amount of action was measured by the quantity of water decomposed: and it was necessary, in order to give validity to the mensuration, to show (as Faraday did show) that neither the size of the electrodes, nor the intensity of the current, nor the strength of the acid solution which acted on the plates of the pile, disturbed the accuracy of this measure. He proved, by experiments upon a great variety of substances, of the most different kinds, that the electro-chemical action is definite in amount according to the measurement of the new instrument." He had already, at an earlier period," asserted, that the chemical power of a current of electricity is in direct proportion to the absolute quantity of electricity which passes; but the volta-electrometer enabled him to fix with more precision the meaning of this general proposition, as well as to place it beyond doubt.

The vast importance of this step in chemistry soon came into view. By the use of the volta-electrometer, Faraday obtained, for each elementary substance, a number which represented the relative amount of its decomposition, and which might properly" be called its "electrochemical equivalent." And the question naturally occurs, whether these numbers bore any relation to any previously established chemical measures. The answer is remarkable. They were no other than

the atomic weights of the Daltonian theory, which formed the climax of the previous ascent of chemistry; and thus here, as everywhere in

21 739.

20 537.

24 792.

"Researches, Art. 371. 22 Arts. 758, 814.

23 877.