appeared. It was only when a considerable time had elapsed after the substitution that hydrogen made its appearance. From several of the above-mentioned facts, it appears that the law formerly laid down, that oxygen gas is only given out at the positive pole of a battery when it is terminated by a noble metal, does not hold good; that the same cause which renders an iron wire indifferent to nitric acid, prevents the oxidation of this metal during the decomposition of water by means of the galvanic battery. I shall not for the present enter further into the theory to be deduced from these facts, as I am satisfied many further researches still require to be made. New Researches on the Properties of Electric Currents, discontinued and directed alternately in contrary directions. By Professor M. A. DE LA RIVE.* It is now three years since I published, in the Memoires de la Société de Physique et d'Historie Naturelle de Geneve, some researches on the properties of magneto-electric currents. I undertook, in that memoir, the task of making a more profound study of certain points, and of analyzing, better than I had been able to do in the former essay, the cause of some of the phenomena which I have there described. I have not lost sight of this engagement, and I feel myself more called on to fulfil it, as my preceding work has been the object of some critical observations on the part of a German philosopher, M. Lenz, to which observations I feel desirous of responding. The title alone which I give to the memoir I now publish is already a response; for one of the most important objections which M. Lenz has made to me is, as will be seen, that of having designated the currents of which I have made use, under the name of magneto-electrical currents, and of having thus attributed, to the fact, that they were produced by magnets, an influence quite peculiar and almost mysterious. Now, as I shall hereafter explain, I have not attached any other importance to the denomination magneto-electric, than that of indicating clearly what was the means by which I had procured the currents which formed the object of my study. I know very well the circumstance which characterised and distinguished them from other currents, and this is the fact of being discontinued and directed alternately in contrary directions. It is this double character which appeared to me to I • The memoir which I now publish will appear at the same time in the first part of tome ix, of the Memoires de la Société de Physique et d'Historie Naturelle de Geneve, under the title of some chemical phenomena which manifest themselves under the action of electric currents devetoped by induction. have solely made some additions and some changes of form. I have in it also retrenched all one part, which I intend to print in the next number of the Archives de l'Ectricite, with more considerable development than those which I have given in the memoir to which I have just referred. give to this species of currents an importance of which experience has to me confirmed the reality, for it has shown me that the employment of them might conduce to the discovery of phenomena of an entirely new order, and of a true interest to the scientific world. Currents discontinued and directed alternately in contrary directions may be developed by many different methods, and not only by magnets. It becomes convenient, then, to designate them by that which constitutes their principal character, either from their essence, so to speak, or rather by some accessary circumstance, such as one of the manners of producing them. This is what I am about to do at present; and I do it much more willingly, as my aim is precisely to endeavour, still more than in my preceding work, to extract from among my experiments, some few experiments which make these currents differ from the ordinary currents of the voltaic pile, with which I shall be called to compare them. Before entering upon the exposition of the new experimental researches which I have made, I shall examine the critical observations of M. Lenz, and endeavour to respond to them. This examination, and these responses, which have naturally led me to take up again some points of my former work, will serve also as an introduction to that part of this second memoir, which contains the new researches. PART FIRST. on my Me An examination of the Critical Observations of M. LENZ, moir, entitled Researches on the Properties of Magneto-Electrical Currents.* M. Lenz has published in the Annalen der Physik, of Poggendorf, some observations on my preceding memoir above referred to; he has classed them under the same heads as my researches are classed. I shall follow exactly the same order in the examination which I am now about to make. 1. General Observations on Magneto-Electric Currents.-M. Lenz commences by combatting the opinion that it is possible to have a specific difference between electric currents of different origin; he does not admit that, amongst these currents, that some of them are more particularly adapted to the production of chemical effects, and others for the production of calorific effects; he rejects the idea that the relation, as to the conductibility of bodies, is not the same for powerful currents as for those of a feebler character. He attributes the errors into which, according to his account, philosophers have fallen, in this respect, to the ignorance prevailing among them of the law of Ohm; a law, the discovery of which appeared to him to be one of the most important which has been made in voltaic electricity. Archives De L'Ectricité, No. 1. Without denying the importance of the law of Ohm, I may be permitted to remark, that it is necessary to distinguish the circumstances which this law has for its object, to appreciate its influence, in the form under which he takes it into account. As to these circumstances, I have enumerated them myself, in a memoir published in the Annals of Chemistry, of March, 1828;* I have expressly indicated that the intensity of an electric current in a voltaic pair, depends not only on the relative energy of the two metals for the producing cause to ascertain the chemical action, according to my theory, but that it depends also on the resistances which the current meets with in its passage through the circuit. I have indicated that these resistances are the imperfect conductibility of the solids, and more especially the liquids which compose the circuit, and the difficulty which electricity has to encounter in alternately traversing liquid and solid conductors. M. Ohm admits that the intensity of the current is a function of two of the three causes of resistance which I have just referred to; but he has done more than I have : he has determined the form of this function. Can this form account for all possible cases? The German philosophers appear to believe it. I have, I avow it, some doubts in this respect; and besides, 1 am far from being convinced that the resistances, more or less great, which a current encounters in the circuit which it has to traverse, are the only causes of specific characters which it presents in its properties. I do not deny that these circumstances play a very important part in the production of these phenomena. In the memoir which I have already cited, in an anterior memoir, published in 1825,† and in almost all the researches that I have made since that time, I have shown the importance of taking these resistances into account. I thus explain the influence of the number and size of the pairs of of a pile, on the different effects which it is apt to produce; I deduce from it the explication of the calorific effects of the voltaic current, § &c. It was after having, at first, believed that the principle of resistances was sufficient to account for all these circumstances, that doubts began to arise in my mind, that I exposed in my letter to M. Arago, inserted in the Annals de Chimie,|| doubts which several experiments of Mr. Faraday, relative to the intensity of currents due to different chemical actions, appeared to me to confirm. I shall not enlarge further here upon this important point, which I intend to treat separately in a future part of this paper. shall confine myself to the resumption of my thoughts, on the subject of the law of Ohm, in saying that it has not yet been proved to me that the principle of this law is perfectly sure; but that, even in * Ann. de Ch. et de Phys., t. xxxvii, p. 251. ↑ Ann. de Ch. et de Phys., t. xxviii, p. 213. I Ann. de Ch. et de Phys., t. xxxix, p. 319, et Memoires de la Soc. de Phys. et d'Hist. Nat., t. vi. Ann. de Ch. et de Phys., t. xl, p. 38. Ann. de Ch. et de Phys., t. xli, p. 38. admitting it, there remains some doubts in my mind on the exactness of the form under which Ohm believed it to be possible to introduce, in the general expression of the intensity of a current, the These doubts are circumstances which determine this intensity. drawn up essentially in the difficulty of isolating, in an absolute manner, each of the determining circumstances, which it is necessary to do in order to know its part in the influence in the numerous anomalies which experiments present; especially when we act on energetic currents, which anomalies it is not always easy to explain; and, in fine, in the intimate connexion which I see exists between chemical action and electric action, and in the agreement which ought to result from it amongst the variations which these latter undergo, and those to which the first are subject. After the general observations which I have just referred to, M. Leaz makes two remarks on the apparatus of which I have made use the first is relative to the nature of the currents which I have studied, the other to the use I have made of the thermometer of Brequet, to measure the intensity of these currents by means of their calorific effect. Here is, as far as I can comprehend, in what consists exactly the first remark. The author seems to believe that I attribute to each of the elementary currents, produced by induction, and not to their joint influence, the properties which I have sought to discover in magneto-electric currents. He has the air of supposing that I consider the origin of these currents, rather than the manner in which they are grouped, as the cause of the phenomena which they present; and he observes that, in consequence, I ought to have studied the effect of each current isolated, and not that of a succession, It is this study which more or less rapid, of these same currents. he himself makes, farther on, and of which the results are not, in point, in agreement with those which I have obtained, by occupying myself on the subject under another point of view. I avow that I do not see why I ought to be obliged to occupy myself on isolated currents, rather than on them altogether. I have an apparatus (that of Clarke), which produces a series of electric currents by induction; I describe this apparatus: I give to the currents which it developes, a name (magneto-electric currents), which, without in any way prejudging of their properties, recalls to the mind the apparatus whence they emanate; I endeavour to analyse their effects; I expose the laws to which these effects appear to me to be subjected. Strictly speaking, I might stop short there, and say nothing of the cause to which I attribute these effects. However, in several parts of my memoir, I have explained myself on this point, and I have always declared an opinion contrary to that which M. Leaz seems to attribute to me, who has badly compreI have said that I attribute hended me, or at least, it appears so. the special properties of magneto-electrical currents, not to their being produced by magnets, but decidedly to the fact that they are inconstant, and directed alternately in contrary directions.* If I have made use of a magnet, in order to procure my currents, it is because I have found that this was the most commodious means, and, at the same time, the most convenient to have them of a constant intensity. I have never denied that currents fulfilling all the same conditions, but produced by another source, do not possess the same properties. The second preliminary remark of M. Lenz, has for its object, I have said, the employment that I made of the thermometer of Brequet, to measure the intensity of magneto-electric currents, by means of the elevation of temperature which these currents determine in the helix of this thermometer in traversing it. M. Lenz remarks, that the current is divided among the three plates of silver, gold, or platinum, which compose the helix, proportionally to their electric conductibility, and consequently unequally, that this current ought also to heat them unequally, so much as to cause this circumstance, since it produces more heat in proportion as the resistances which it meets with are greater. He concludes from it, that the phenomenon of the heating of a helix in Brequet's thermometer, by the electric currents, is a very complicated phenomenon, and that we cannot make use of this means to measure the intensity of currents. I admit, with M. Lenz, that it is very possible that the current is not distributed uniformly among the three metallic plates which compose the helix; but I do not conclude from that, that the three plates have not exactly the same temperature. I remarked, at first, that the two circumstances, which are indicated as previously determining a different temperature in each plate, compensate the one for the other; for if, on one hand, the plate of less conducting power transmits less electricity; on the other hand, it becomes heated more by the action of the same current, by virtue even of the greater resistance which it presents. Besides, whatever be the mode of distribution of the current, it is impossible that the elevation of tem.. perature which results from it is not the same in each contiguous • This is what results from several passages of my memoir, especially the following:-Thus, after having described the apparatus of which I made use, I add: "We can, by an artifice, make one of the two currents disappear alternating contrary, in such a manner as only to have a series of currents all directed in the same direction; but they then lose a great part of their energy, and some of their most remarkable properties." Here is a plain proof that I consider the fact that these currents are directed alternately in contrary directions, as the cause of some of their most remarkable properties." Afterwards, in speaking of the physiological effects, so called, of these currents, I say: "It appears that the power of these currents is essentially due to their inconstancy; for we know that, when a current acts in a continuous manner, whatever be its intensity, the animal submitted to its action only experiences commotions at the moment when this action commences, or at the instant it ceases. Farther, we can obtain the same effect in rendering inconstant, by means of a very simple artifice, the current developed by a simple voltaic element." |