wheel and a band; the points of the wheel touching in succession a copper spring in connexion with the positive surface, and thus producing a discharge at every contact of the wheel and copper spring.

When the two surfaces are connected by wires with two basins of salt water, and the hands immersed one in each basin, the effect experienced is precisely that of a discharge of a voltaic battery. The discharges can be made in such rapid succession as to prevent the sensation of distinct shocks; and if the process were to be concealed it would require some experience to distinguish between the effects on the animal economy from this apparatus and those from a voltaic battery charged with acid and water.

My views being so far verified, the next attempt was to simplify the apparatus and make it more portable; and as it was readily seen that if one hundred pairs would charge glass of considerable thickness, thinner glass might be charged by fewer pairs; this was done : and eventually the glass entirely dismissed, and its place supplied with well-varnished Bristol-board. These boards answer exceedingly well as a reservoir for low intensities; they may be coated to within an inch of the edge all round, and placed upon their edges either on a piece of glass, or on a board properly prepared, and arranged to any required extent like the plates of a voltaic battery, but when considerable intensity is wanted, it is better to use thin glass.

From these facts we learn that metallic surfaces of many acres of extent may possibly be charged to a low intensity in the interior of the earth, by having a thin intervening stratum of inferior conducting matter sufficient to insulate from each other their dissimilar electric surfaces.

It may now be understood that the slightest accident which would suddenly break through the insulation, such as the sinking of a mass of metalline matter from one stratum to the other, would cause a sudden rush of an immense ocean of the electric fluid, which might be productive of subterranean lightnings and tremendous explosions, sufficient to shake an extensive range of country on every side.

Connected with the preceding facts there are others which may be conveniently mentioned in this place, and which would lead us to similar explanations of the cause of subterraneous convulsions. Electric currents of considerable magnitude when suddenly checked, or diverted to a new channel, produce a momentum not very generally understood; but which I will endeavour to explain. A coil of copper wire, excited by magnetic action, will become a channel for an electric current; and whilst the whole circuit is metallic, the velocity of that current would be considerably greater than if any, even a small part, of the circuit were of worse conducting materials: and if the current were suddenly transferred from a channel of the former character to one of the latter, by any contrivance whatever, it would meet a resistance on entering the new channel, which the momentum it had previously acquired would have to overcome; and a sudden disturbance of the electric fluid,

previously at rest, would take place, and a violent rush of the current would as suddenly follow.

It is in this manner that shocks and sparks are produced by magnetic electric machines, where the current, previously in rapid motion, is suddenly transferred to a new channel of inferior conducting character; and all the fluid in the revolving coil rushes through a person properly situated for the new route, and who experiences the electric shock, or else through a thin stratum of air at an interruption in the metallic circuit where the spark is produced.

These, then, are some of the effects of electric currents, or of the momentum of the electric fluid in a state of motion, after the exciting cause is entirely cut off. The shock thus produced may very conveniently be compared to the blow given by Montgolfier's hydraulic ram. Electro-momenta may be produced by any mode of excitation whatever, and the effects will be proportional to the velocity and quantity of the electric fluid first put into motion; and the length of the original channel is also to be taken into account. If then electro-momenta, capable of producing violent shocks and vivid sparks, can be produced by a few hundreds of feet of thin copper wire, what is it that might not be expected from the electro-momenta of nature, arising from currents of many miles in extent, kept in motion either by heat, saline solutions, or by other causes, amongst the metalline strata below the surface of the earth? A sudden disruption in the circuit would insure the blow, and an earthquake might be the result.

Artillery Place, Woolwich, July 4, 1836.

Letter from M. EDMOND BECQUEREL to the Editors of the “Annales de Chimie et de Physique."

In the "Annales de Chimie et de Physique," for December, 1841, I gave a notice on voltaic batteries of continuous action, in which I stated such facts on the subject as have resulted from the experiments of those natural philosophers who have been engaged in these enquiries.

Mr. Daniell supposing that I had not done him justice, has thought proper to reply to several of my statements in the "Philosophical Magazine," for April, 1842. It was far from my intention to state any thing displeasing to Mr. Daniell, or to misrepresent facts, or to claim for my father a discovery to which he had no right. In this particular Mr. Daniell has unaccountably mistaken my motives for publishing my notice, and had it not been for this circumstance I should not have thought proper to reply to him at this time; for, as regards the principal points in the facts which I mentioned, I have nothing whatever to alter.

"Annales de Chimie et de Physique."

† See "Annals of Electricity, &c." Vol. viii, p. 456.

In every physical question, three particulars are to be taken into consideration: the idea, the principle, and the application. Now, it is proved by well ascertained facts, that from 1829, and even several years previously, my father had invented and constructed voltaic batteries of constant action; though it be true that they had not the extent of action, and the other advantages possessed by those batteries which Mr. Daniell made known in 1836. The apparatus invented by my father immediately obtained the appellation of "Constant Voltaic Batteries ;" and as they still answer the purpose he then intended, to contend with him now about either the idea, the principle, or the application, within certain limits, would be perfectly ridiculous.

Respecting the priority of invention, the details which I am about to give, will, I think, leave no farther doubt on the subject. For more than fifteen years the electro-chemical reactions, by means of which my father was enabled to produce crystallized substances, were carried on by the employment of a small piece of apparatus consisting of tubes bent into the shape of an U, closed at the bended part by a partition of moist clay, for the purpose of keeping separate the two liquids which occupied the branches of each tube: in one of which was placed a solution of sulphate, nitrate, or chloride of copper, in which a plate of copper was immersed. In the other branch was placed a solution of sea salt and a plate of zinc, or some other metal. Such is the arrangement of the simple apparatus which is known to the scientific by the name Pile d Cloison.

The figure of this apparatus is of but little importance, as it may be varied at pleasure without altering its principle or mode of action. Instead of an U tube, for example, we may employ any kind of vessel, formed into two compartments by a diaphragm of bladder, baked earth, plaster, linen, or other fabric, &c.; but all such variations are necessarily on the principle of the U tube.

After the year 1829, long before Mr. Daniell published any thing on the subject, my father made several communications on this subject to the Academy of Sciences: and the description of an apparatus of this kind, which maintained a constant current for two entire days, is to be seen in the " Compte Rendu des Séances," for 1835. According to this fact, therefore, Mr. Daniell can have no pretentions to the discovery of the general principle on which the operation of the "constant voltaic battery" entirely depends; but he may justly claim the good arrangement that he has given to this battery, and, amongst others, the advantage of preserving a saturated solution of sulphate of copper, and of obtaining more energetic effects than those for which my father had any occasion, at the commencement, for the production of crystallized substances analogous to those formed by nature; a discovery for which he received the Copley Medal from the Royal Society of London, and which Mr. Daniell also received some time afterwards, for his form of the constant voltaic battery.

Notwithstanding these facts, so long before the public, and so self-evident as not to be mistaken, Mr. Daniell declares that, in the construction of his battery, he was not guided by the works of his predecessors, and that the principles which he adopted are different from those which my father had so long since employed. He states, for instance, that the rapid diminution and early cessation of the current by ordinary batteries, are due to the deposition of zinc on the negative plates of each pair. On this point we perfectly agree: the annihilating counteraction occasioned by the deposition of zinc upon the copper plates comes under that called polarization of the electrodes (an odd enough expression). In my notice I mention that "each negative plate (of copper or platinum) retains on its surface alkaline elements, such as hydrogen, liberated by the decomposition of water, and bases liberated by the decomposition of saline substances dissolved in the water." This phrase does not exclude any of the bases; therefore, the zinc liberated from the salt of zine must also be deposited on the negative plate; a fact known many years ago, and by Sir Humphry Davy shown to be the cause of the action of Ritter's "secondary piles." This decomposition being effected, the action of the liquid on the zinc necessarily gives birth to a counter current, which gradually destroys the action of the primary one. Therefore, in order to obtain an apparatus of continuous action, it was necessary to devise some means to prevent the zine and the alkalies being deposited on the negative plates.

Mr. Daniell next says, that the passage of the electric current across the diaphragms of bladder is well known to experimentalists, and quotes Dr. Ritchie as having made use of them. To this I reply, that the use of diaphragms in physics is very ancient, since one of the Bernoullis had already separated the different liquids by a membrane, in an experiment intended to produce endosmose effects. Porret also adopted the same means for the purpose of showing that in separating, by means of a membrane, a mass of water into two parts, and by immersing in each a platinum plate connected with the poles of a battery, the current would cause the water in the positive cell to traverse the membrane and arrive in the negative cell. I might still give other examples were it necessary. The use of membranes and other diaphragms for transmitting constant currents was brought into use by my father nine or ten years before Mr. Daniell was engaged in such enquiries; as the experiments communicated to the Academy of Sciences, on the 23rd February, 1829, will amply testify.

As to the publication of Dr. Ritchie in the "Philosophical Transactions," it is dated May, 1829, and, consequently, some months later. I therefore look upon Mr. Daniell's battery, although very convenient, as based upon the same principles as the apparatus employed by my father for several years previously.

"Annales de Chimie et de Physique," t. xli.

Farther on, Mr. Daniell adds: "Even in the use of the diaphragm, which might at first sight appear similar, there is a 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."

I confess that I know not how Mr. Daniell can keep separate two liquids by a membrane moistened by them and which they can penetrate, without that passage from one to the other taking place which is otherwise called endosmose and exosmose. Indeed, it is impossible to realise this condition. The only means of retarding the mixture of the two liquids, as long as possible, is by substituting for the membrane a thick diaphragm of clay, as did my father: the intensity of the current is certainly diminished, but uniform effects are obtained which may continue for months or even years.

Mr. Daniell further says: 66 and I repeat, that in my constant battery nothing depends upon the contact and action of the two liquids upon each other."

I do not understand this assertion: for every one knows that two different liquids acting upon each other by an intermediate membrane, disengage electricity enough to produce a current; and if Mr. Daniell wishes to convince himself of the fact, he has only to take away, in one of his pairs, the plates of zinc and of copper, and substitute for them two plates of platinum; he will have a current owing to the reaction of the two liquids upon each other, less intense, indeed, than that derived from a pair, one of which is an oxidable metal.

Mr. Daniell also says that, "the amount of force obtained by my father's apparatus is insignificant as respects its application to the arts."

I will reply yes and no to him: yes, if there be a question of apparatus like that of Mr. Daniell, intended to produce currents which are to be transmitted into liquids placed in separate vessels : no, if the currents are to re-act chemically on the liquids which themselves form a part of the apparatus.

In short, the apparatus constructed by my father, six years ago, for the treatment of the ores of silver, lead, and copper, are based on the same principles that I have before explained; and these apparatus are of much more considerable dimensions than that of Mr. Daniell, since each pair requires 1,000 litres of liquid for its excitement, and six of these pairs have been united into one battery : therefore 6,000 litres of liquid have been employed at one time: and the energy of this apparatus has been still greater than that produced by Mr. Daniell's battery: for all the silver and lead contained in these ores, amounting to about one kilogramme of silver, and 100 kilogrammes of lead were extracted in the space of a few hours.

I now leave it to the judgment of the reader who is in the right,