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nor even by altering the name of the “ constant battery" to that of the “sustaining battery.

I will embrace this opportunity of observing that M. Becquerel, in his Traité de l'Electricité (tome v, livre xiv, p. 195), has inadvertently committed an error affecting the history of “the constant battery," in giving priority to Professor Grove's experiments with the nitric acid battery over mine. He describes that gentleman's construction, and then proceeds, “ Les choses en étaient lorsque M. Daniell a repris la question, qu'il a analysé avec sagacité. Ses recherches l'ont mis à même de doter la science d'une pile construite d'après les principes précédentes, et qui est aujourd'hui généralement adoptée dans les expériences de physique."*

It is only necessary to recall the data of my first paper upon the subject in the Philosophical Transactions, viz. February 11th, 1836, and that of Professor Grove's communication to the French Academy, I believe, April 1839. Professor Grove has never spoken of his battery but as the further application of principles which I had previously deduced.

In conclusion, I cannot but express my regret that the filial piety of M. Edmond Becquerel should have betrayed him into an act of injustice by preferring a claim for his father which is totally unsupported by the facts of the case, and from which his well earned reputation can derive no permanent extension.

I remain, dear Sir, very faithfully your's, King's College, London, March, 1842.

J. F. DANIELL.

On the Sustaining Voltaic Battery : in reference to some Observations

of Professor Daniell, in the April Number of the Philosophical Magazine."+ By F. W. Mullins, Esq., M.A., &c.

To WILLIAM STURGEON, Esq. Dear Sir--As the conductor of a magazine, justly denominated the “Guardian of Experimental Science," I trust you will kindly make room for a few observations called forth by the following paragraph contained in the letter of Professor Daniell, “On the Constant Voltaic Battery," published in the Philosophical Magazine for March.

After setting forth the differences between the principles of the “constant battery," and M. Becquerel's voltaic combination discovered in the year 1829. Mr. Daniell adds : “But of course the

" These particulars were there when Mr. Daniell again took took up the question, which he has analyzed with sagacity. His researches hare endowed science with a pile constructed after the preceding principles, and which is generally adopted in philosophical experiments."

† The preceding article is that alluded to. Professor Daniell's voltaic arrangements and experiments are fully described in vols. 1 and 3 of the Annals of Electricity, 80.-Edit.

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principles of the construction are independent of form and materials, and are capable of application to flat, square, and equal surfaces of the two metals, as well as to concentric arrangements. They admit also of the employment of different metals, and of different electrolytes. They are not changed by placing the zinc on the outside instead of the inside of the copper, nor even by altering the name of the constant battery to that of the sustaining battery.

Now, as it is quite clear that the latter part of this paragraph distinctly refers to “Mullins's Sustaining Battery,” that being the distinguishing appellation applied to it by me, and borne by it alone, and as the inference to be drawn from the entire sentence is, that the principles of the "constant" and "sustaining ” batteries are not only identical, but that the latter arrangement has been borrowed from the former-I cannot permit such an impression to acquire further publicity, without at once entering my protest against the correctness of such a conclusion, as well as against the mode in which it has been put forward.

I find a similar misstatement in Walker's Electrotype Manipulation, but I have not thought proper to notice it, nor should I do so on the present occasion, did I not find Professor Daniell himself using language which might be understood to sanction inuendos incapable of proof, and utterly groundless.

Sir, I formally and distinctly deny that the principles of the “sustaining” are the same as those of the “ constant voltaic battery;" and I cannot but consider it extremely strange that Professor Daniell should hazard such an opinion in a letter written professedly for the purpose of showing (as in the case of Becquerel's battery and his own) that voltaic combinations, although constructed of exactly similar materials, with the similar design of obtaining constancy of effect, may yet have no one principle in common !!

But as facts are stubborn things, and as I like to deal with facts, and not opinions, let me first state, in Professor Daniell's own words, what are the principles of his combination, and then explain those of the other.

First then, Mr. Daniell declares his “constant battery to be constructed on the principle of a central disposition of the active metal, with regard to the conducting surface," and he carries out this principle in his battery, by the employment of a rod of cast zinc, amalgamated and suspended in the centre of a circle of copper, the said rod being, according to his detailed measurements, half an inch in diameter, and the copper cylinder surrounding it, three and a half inches ; which the Professor states, “ experience has proved to afford the most advantageous distance between the generating and conducting surfaces.”+ He thus interposes, it would appear, by preference, an imperfect conductor of one and a half inches interval between the metals; this interval, of course, continually increasing

• See his Chemical Philosophy, page 438, sec. 737.
+ See latter part of sec. 737, in Chemical Philosophy.

in proportion to the destruction of the central zinc, and consequently, causing additional retardation of the current. Yet he lays it down as an incontrovertible position, that such an arrangement developes more electric energy, and is more constant in its effects, than equal surfaces of similar metals in any other mode of combination. Now, in the “sustaining battery," these principles of Daniell's are directly opposed by the nature of the arrangement, in which there cannot be any such thing as “central action," and in which retardation is diminished by approximating the metallic surfaces as much as possible : so that, in place of one inch and a half, as in Daniell's arrangement, they shall be no more than a quarter, or at most, half an inch asunder: a principle at variance with Daniell's; grounded on the results of careful experiments, and supported by the distinguished authority and varied investigations of Davy and Faraday, Hare, De la Rive, and many other eminent philosophers.* Secondly, Professor Daniell advocates the use of an acidulated solution in contact with the zinc, which he declares it is requisite to amalgamate, in order to avoid local action ; whereas in the sustain-ing battery, no acids are used, alkaline solutions being employed as far preferable: the zinc is not amalgamated, there being scarcely any local action : rolled instead of cast metal is advantageously used, and the general chemical effects are different. Again, Professor Daniell asserts another of his principles to be, “that of perfectly preventing the mixture of the liquids on the opposite sides of the diaphragm employed," such mixture " producing strong local action,&c.; whereas, in the sustaining battery, a diametrically opposite principle was from the very first brought into play, by the employment of the very thinnest membranes that could be procured it it being found that the mixture of the fluids, within a certain limit, increased considerably the effect; this mixture arising in a great degree, from the action of “endosmose;" which, according to M. Dutrochet, has most probably an electric origin, and, according to my observations, unquestionably promotes electrolysis ; and this principle, the very opposite of Daniell's, was further carried out by the employment of white silk as a diaphragm, which would be superior to every other I know of, but for the disposition of the precipitated copper to collect within its interstices.

Having thus briefly, but I trust clearly, set forth the principles upon which the sustaining battery was constructed, and shown that they are altogether opposed to those claimed by Professor Daniell, I leave it to him and M. Becquerel to settle the question of originality as best they can ; for my part, I make no claim to originality in regard to the principles which governed the construction of the bat

• We have, for many years, employed batteries in which five pairs occupied one inch only of its length.-Edit.

+ Those membranes were abandoned solely in consequence of their liability to injury; wooden diaphragms have been substituted by me, which admit of a certain mixture of the liquids, and are extremely durable.

tery: principles long established by the researches of distinguished men at home and abroad : but I do claim the merit, whatever it may be, of the conclusions drawn from those principles as developed in the particular voltaic arrangement alluded to.

It only remains for me to add, that even supposing the principles of construction of the “sustaining ” battery were identical with Daniell's (which they are not), it would be extremely unfair to ar-' gue or assume that Mr. Daniell's researches furnished the clue to the plan of the other combination ; for I unhesitatingly assert that for years before Daniell’s constant battery was known, every,reader of the Annales de Chemie et de Physique, tome 41 (myself amongst the number), must have been fully aware of Becquerel's discovery in the year 1829, of the possibility of obtaining an equal current for a comparatively long period, by the employment of two fluids : one a solution of a salt of copper, the other diluted sulphuric acid, with a membrane (baudruche) interposed.* In this combination the true principle of a sustaining battery was, beyond question, established ; and although by reason of certain mechanical defects in the construction of Becquerel's batteries, as admitted by himself, the energy was not sustained, so long as it now is, by improved mechanical arrangements, I do insist that to Becquerel is justly and fairly due the honour of being the first promulgator and constructor of a constant voltaic combination of elements or materials similar to those subsequently employed by Daniell, and with the exception of the alkaline solution, similar also to those employed by me.

One word more, and I have done. Mr. Daniell sets forth in the letter alluded to, the “real principles of the constant battery ;” and, inasmuch as he claims originality for those principles, and hints pretty broadly that such original principles have been made use of and applied by others in combinations claimed by them as equally original, it may be well to give, in his own words, his statement of the first of those principles, and answer him in the words of another, whose scientific reputation fully equals his own. Mr. Daniell says, in the first place, “I traced the origin of the decline and ultimate annihilation of the current in the common voltaic battery, not to the evolution of acid and alkaline matter at the opposite plates, and the consequent establishment of a counter current by their mutual reaction, but to the deposition upon the conducting plate of a substantial coating of pure metallic zinc; in consequence of this, zinc becomes opposed to zinc in the circuit, and all current is stopped.Dr. Roget, in his Treatise on Galvanism, published in 1832,+ page 14, after describing the effect produced by the contact of the metals in the circuit, proceeds as follows :-" The disengaged hydrogen will now appear upon the surface of the copper in place of the zinc,

• Our readers may expect a translation of Becquerel's paper in an early number.- EDIT.

+ See Treatise of Galranism in the “Scientific Treatises of the Society for Diffusion of Useful Knowledge."

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without, however, apparently affecting the copper. In process of time, indeed, when a considerable proportion of sulphate of zinc has been dissolved in the fluid, the quantity of disengaged hydrogen is found to diminish, and a thin film, composed partly of metallic zinc, and partly of filaments of oxide of zinc, is deposited on the surface of the copper : as soon as this happens the galvanic action ceases."

I need not here advert to Sir H. Davy's distinct statements on the same subject, for I believe they are too well known to need repetition : suffice it to say, that the deposition of metallic zinc upon the conducting surface, and other causes of the decline of voltaic energy were well understood for years before Professor Daniell produced the constant battery.

Mr. Daniell proceeds to say, that “his next principle was to prevent the deposition of active metal upon the conducting metal, by dividing the portion of the electrolyte in contact with the zinc, from that in contact with the copper, by a porous diaphragm, by which the solution of zinc is prevented from reaching the copper. Now, if deposition of zinc were the sole or chief cause of the decline of voltaic energy, one fluid, so divided, would have answered every purpose ; but this was not so, therefore it appeared requisite to introduce the salt of copper. But it so happens, that when a cupreous salt is employed, though there should be no diaphragm, there is no deposition of zinc on the conducting metal; and I have found, and M. De la Rue and others have proved, that the energy of the battery so charged, may be sustained for a long period without any diaphragm; therefore, upon the ground of preventing deposition of zinc, Mr.'Daniell's protection of the negative metal was unnecessary, and therefore that part of his principle cannot be sustained. For the above reasons I did not adopt a diaphragm "for the purpose of preventing a deposit of zinc upon copper," but for the directly opposite purpose of preventing a deposition of copper upon zinc.

Regreting that I have been compelled to thus defend myself from most unwarrantable insinuations, as well as support my just title to whatever merit may attach to a form of voltaic combination which, for sustained as well as powerful effects, is now pretty generally appreciated ; and assuring Professor Daniell that I have no wish to deprive him of any credit to which he may be fairly entitled; or to insinuate that he read, or had read him, or heard of M. Becquerel's researches, as published in the Annales de Chemie, tome 41, or subsequently, either in the Annales, or any other scientific work, foreign or domestic—I feel that I have stated quite sufficient to prove that I am no imitator of the Professor, and shall, therefore, not be again induced to notice such uncalled-for attacks, no matter from what quarter they may emanate.

I am, dear Sir, your's faithfully, Bruxelles, April 9, 1842.

F. W. Mullins. • A full description of Mr. Mullins's “ sustaining battery" may be seen in rol, I of these Annals.-Edit.

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