zinc to zinc in the acid is sufficient to account for the result without supposing "the reaction of alkaline matter transported to the conducting plate upon acid transported in like manner to the zinc plate through the intervening fluid." It is difficult, indeed, to conceive that the latter should not rather increase the power of the direct current, by its action upon the zinc with which it must be in contact, than produce a counter current by its action upon the alkaline matter upon the distant platinum plate.

The problem of a constant battery, which M. E. Becquerel says that his father has solved, is thus stated :

"Si donc ou pouvait enlever continuellement les élémens alcalins et acides qui se déposent sur les lames, on anéantirait le courant secondaire, et la pile aurait une intensité constante, en tant cependant que les surfaces des lames resteraient à peu près aussi nettes et que l'action du liquide sur le zinc serait à peu près la même." (P. 438).*

It appears from the statement of M. E. Becquerel, that in the year 1829 his father contrived an apparatus consisting of a glass cell or rectangular vessel, the interior of which was divided into three compartments by two diaphragms of gold-beater's skin, admitting of no communication except through the membranes placed for the purpose of retarding the mixture or combination of the liquids con

tained in each.

The bottom of the cell was perforated only in the centre compartment by a small opening, so that upon plunging the cell into another vessel containing a conducting fluid, the liquids in the two extreme compartments would mix with great difficulty: the central aperture admitted also of being closed, and the middle compartment could then be filled with the liquid of one of the extreme compartments. A plate of zinc was immersed in one and a plate of copper in the other, and the two were placed in metallic communication by means of the wires of a galvanometer.

Under these circumstances, when all the compartments were charged with dilute sulphuric acid (th acid), a deviation of the galvanometer needle was produced, which, as with an ordinary couple, gradually decreased. Upon consulting M. Becquerel's original memoir (Ann. de Phys. et de Chim., tome xli, p. 21), I find the following tabular record of the results :—

• "If then we could continually remove the alkaline and acid elements which are deposited on the plates we should annihilate the secondary current, and the pile would have a constant intensity, inasmuch, however, that the surfaces of the plates would remain also almost clear, and the action of the liquid on the zinc would be almost the same."

Upon re-commencing the experiment with the addition of th nitric acid to the dilute sulphuric acid in the copper compartment, the intensity of the current changed, but gradually diminished as in the following table :

Upon the substitution of nitrate of copper for the nitric acid, the results were sensibly the same. M. Becquerel varied these experiments in many ways, and with the aid of this apparatus arrived at the following conclusions:

:

"The maximum of intensity is obtained by immersing the copper plate in a solution of nitrate of copper, and the zinc in a solution of sulphate of zinc, but there is also a diminution with time; a little less rapid however than with an ordinary couple.”

The following is the table of the last results :

The next paragraph of M. E. Becquerel's Notice I will give in his own words for fear of mistakes:

:

"Si l'on met de l'acide nitrique étendu dans la case zinc, un peu d'eau et d'acide sulfurique dans la case cuivre, et que dans la caisse A A'on n'emploie qu'un diaphragme, ou que l'on rapproche les deux diaphragmes de telle sorte que l'acide nitrique de la case zinc puisse passer lentement dans la case cuivre, afin d'augmenter la conductibilité, alors on peut, au lieu de rendre les intensités décroissantes les rendre croissantes pendant la première demi-heur; cela dépend de la quantité d'acide nitrique versée dans la case zinc ; si l'on en met avec précaution, on peut arriver à obtenir un courant constant pendant une demi-heure ou une heure. Cette disposition du couple réalise donc pendant un certain temps le résultat que nous avous annoncé, c'est-à-dire détruit le courant secondaire; car l'acide nitrique qui se trouve dans la case zinc s'empare constamment du cuivre de la solution, qui, après avoir traversé les diaphragmes, se dépose sur le zinc. "Ainsi ces expériences montrent la possibilité d'obtenir un courant constant en détruisant le courant secondaire.” (P. 440).*

"If we put diluted nitric acid into the zinc case, and a little water and sulphuric acid in the copper case, and that in the box A A, we only employ a diaphragm, or that we bring towards each other the two diaphragms in such a manner that the nitric acid of the zinc case may pass slowly into the copper cell, in order to augment the conductibility; then we can, in place of rendering the intensities decreasing, render them increasing during the first half-hour: this depends on the quantity of nitric acid poured into the zinc cell; if we put the nitric acid in with precaution we may be enabled to obtain

Now, most assuredly, the principles and results derived from these experiments are not the principles and results of "the constant battery" they are not the principles and results of my battery, which M. Becquerel has nevertheless described as- -"construit d'après les principes exposés précédemment," and, as one amongst other similar ones, "d'un usage plus facile et dont l'action est constante pendant un temps plus long." (P. 444).

The amount of constancy which M. E. Becquerel obtained, and the certainty with which he obtained it, are thus described in his original memoir :-

66

"Il m'est arrivée plusieurs fois d'obtenir une compensation telle que les déviations de l'aiguille aimantée étaient constants pendant une heure, avantage que l'on n'a jamais avec les piles ordinaires ;' and M. E. Becquerel, as we have just seen, says that "by adding nitric acid with precaution one may manage to obtain a constant current for half an hour or an hour."

With my constant battery, constructed with siphon tubes, as described by M. E. Becquerel, a steady current might be kept up, if necessary, for a week together, provided a proper supply of materials were furnished; and the amount of force set in action by it would be measured, not by some 60° of the galvanometer, but by the number of yards of platinum wire which it would fuse or render red-hot.

Even in the use of the diaphragm,† which might at first sight appear to be similar in the two constructions, there is direct opposition; for my object is to keep the two electrolytes which I employ perfectly separate, so that no portion of one may penetrate to the other, except in the process of electrolysis; while, according to M. Becquerel's principles, it is necessary that they should slowly mingle; and the diaphragm is placed to regulate the mixture. In his own words it is necessary "que l'on approche les deux diaphragmes de telle sorte que l'acide nitrique de la case zinc puisse passer lentement dans la case cuivre."

a constant current during half an hour or an hour. This disposition of the couple realises then, during a certain time, the result which we have announced, that is to say, it has destroyed the secondary current; for the nitric acid which is found in the zinc case seizes constantly on the copper of the solu tion, which, after having traversed the diaphragms is deposited on the zinc. "Thus these experiments show the possibility of obtaining a constant current by destroying the secondary current."

"I have been enabled several times to obtain such a compensation that the deviations of the magnetic needle were constant during an hour: an advantage which we never obtain with the ordinary piles."

+ The passage of the voltaic current through diaphragms of bladder was well known to experimentalists before the publication of M. Becquerel's researches. The late Dr. Ritchie, amongst others, made frequent use of them; and in the Phil. Trans. for 1829, p. 363, there is a paper by that gentleman, in which "a small rectangular box divided into two compartments by a diaphragm of bladder " is described, which was used for the purpose of exposing the plates of a galvanic circle to two different liquids.

The purpose which the nitric acid is said to effect, is to me perfectly incomprehensible, namely, that of "taking up the copper of the solution, which after having traversed the diaphragms is depo-sited upon the zinc."

According to my experience, under these circumstances the deposited copper would be untouched, and the local solution of the zinc greatly promoted: but my present object is not to controvert M. E. Becquerel's statements further than is necessary to show that the principles which he has derived from his father's experiments are not the principles of my "constant battery."

M. Edmond Becquerel, however, seems to have some misgivings that the premises upon which he has founded his father's claim may not be deemed sufficient for the purpose; for he proceeds

"Ainsi ces expériences montrent la possibilité d'obtenir un courant constant en détruisant le courant secondaire; c'est-à-dire en faisant plonger les lames dans des liquides différents. Plus tard mon père a résolu complètement la question." (P. 440).*

This complete solution of the problem is comprised in the apparatus which M. Becquerel has named "chaine simple à oxygène." It consists of two small glass vessels, of which one contains a concentrated solution of caustic potassa, and the other a solution of strong nitric acid. These two vessels are connected together by a bent glass tube fitted with porcelain clay wetted with a solution of sea salt. In each vessel is placed a small plate of platinum; and when a metallic communication is made between the two, a current is established of sufficient energy to cause the evolution of oxygen from the plate in the potassa, while the equivalent hydrogen is absorbed by the nitric acid at the opposite plate. When the communication is made between the plates by means of a galvanometer, the needle is deflected. This slow current will remain constant for twenty-four hours, or longer; but it ceases when the nitrate of potassa formed in the connecting tube crystallizes.

Now, it will be observed, that the porous diaphragm is here again employed, not to produce, as in my "constant battery," as complete a separation as possible between the liquids, but to regulate their mixture, which is essential both to the production of the primary current and, according to M. Becquerel, to the destruction of the secondary one.

"Il faut que les métaux qui composent chaque couple plongent dans des liquides différents, séparés par une membrane ou un diaphragm capable de laisser traverser peu a peu les liquides, cette disposition étant la seule par laquelle le courant secondaire produit

"Thus these experiments show the possibility of obtaining a constant current by destroying the secondary current; that is to say, in causing the plates to be immersed in different liquids. At a later period my father completely resolved this question."

par la polarization des électrodes puisse être détruit." (P. 442.)* M. E. Becquerel, however, allows that even this apparatus, which so completely solves the problem of the constant battery, is incapable of application.

"Ce dernier appareil résout complètement la question sous le point de vue scientifique, mais pour les applications le courant électrique n'aurait pas une énergie suffisante, car alors il faudrait de plus grands éléments et en plus grand nombre, ce qui serait assez coûteux."

He adds, "il s'ensuit que ces appareils, qui forment pile, ont une intensité d'action constante pendant un temps considérable: cette condition n'est remplie que quand l'action est très lente." (P. 442).†

It is difficult, indeed, to conceive that M. E. Becquerel can be serious in attempting to trace an analogy between this arrangement, or any of the similar apparatus formed of "tubes en U," which his father has so successfully applied to the investigation "des actions. lentes," and "the constant battery;" whose object is the generation of voltaic power, with a constancy and rapidity which promises to render it applicable not only to manufacturing but mechanical purposes.

The very source of the current in the "chaine simple à oxygène," is different from that of "the constant battery." M. Becquerel, in his Traité de l'Electricité (tome iii, § 526), ascribes it to the slow and direct combination of the acid and alkali; but this explanation will not be deemed satisfactory, since Dr. Faraday has shown that the decomposition and polarization of the molecules of an electrolyte are essential to the establishment of a current. I have myself suggested an explanation of the undoubted phenomena of current and decomposition which take place, which is quite compatible with these conditions (Phil. Trans. 1840, p. 223). The origin of the force is, however, doubtless, to be found at the point of contact of the two liquids, and not at the electrodes; and I repeat, that in my "constant battery" nothing depends upon the contact and action of the two liquids upon each other.

The amount of force is also perfectly insignificant with regard to its application to the arts. It would be difficult to obtain by this arrangement a decomposition amounting to th of a cubic inch of

"It is necessary that the metals which compose each couple are immersed in different liquids, separated by a membrane or a diaphragm capable of allowing the liquids to traverse little by little, this disposition being the only one by which the secondary current produced by the polarization of the electrodes can be destroyed."

"The latter apparatus completely resolves the question in a scientific point of view; but for its applications, the electric current will not have sufficient energy, for then it would be necessary to have larger elements, and in a greater number, which would be expensive."

He adds, "It follows that these pieces of apparatus which form the pile have a constant intensity of action during a considerable time; this condition is only fulfilled when the action is very slow."