communication with either the ground or the negative extremity of the column, by only changing the position of a brass wire 29, hooked to the extremity of the horizontal brass piece. In the position of this wire, as represented in the figure, the ball 18 and the silver wire 21 are in communication with the ground; and when it is wanted to make them communicate with the negative extremity of the columns I have only to take up the moveable wire, and to lay its end on the projecting brass piece of that extremity. I was surprised to find so little difference of effect between the communinication of the ball 18 with the negative extremity of the columns, and with the ground, which is a standard between the negative and positive state of bodies; and upon the whole this kind of observation opens a new and interesting field of researches. Therefore, though I had but a short time to follow these observations, the following journal will show at least the nature of this phenomenon.

In the last days of these observations I had some reason to suspect that something had been deranged in the apparatus, but I could not examine it, as I was preparing to leave Windsor for spending the summer in Devonshire, where I write this paper. However, the defect which I suspected did not interfere with the object of this last series of observations, which principally relates to the electric state of the ground. This state is here compared with that of the extremities of the column, which I have called negative, though it is sometimes neutral, comparatively with the electric state of the ambient air; but it is never positive. On the other hand, the bead never moves but as positive comparatively with the same standard, and it moves the faster as the ball 18 differs more from its electric state. Now it is seen in the above observations, that sometimes the bead moves faster when the ball is in communication with the ground, than when it communicates with the extremity of the column called negative. This is a test of the electric state of the ground which deserves to be deeply studied, in order to understand it better.

Were I younger, I ought not to publish these experiments and observations in their present state; I should endeavour first, to improve the instrument, in order to meet a proper season with more advantage; then to follow the motion of the aerial electroscope more regularly than hitherto I have been able to do, being constantly employed in improving it; and to study the connexion between these motions and the changes in the electric state of the air near the ground, and of the ground itself: a course of observations, which is to be followed from the time of the greatest effects of the column, to that of their rapid diminution, coinciding with the time when vegetation, the greatest terrestrial phenomenon, prevails on all the ground; and in which it thus appears that the electric fluid has some influence. But though it is possible that I may take up again these observations, I prefer an earlier communication to natural philosophers of the beginning of researches of this class; because at any rate these researches would advance more certainly, should they become the object of many observers, not merely for assembling scattered and unconnected phenomena, but for considering the light that they reflect upon each other, which may help to trace up their real causes. No spontaneous effects can manifest in

a more characteristic manner these remote connexions between terrestrial phenomena by common causes, than those offered to our view by the atmosphere, in which, therefore, we must endeavour to extend our knowledge by meteorological observations and as these phenomena have been for a long time one of the principal objects of my attention and study, I purpose to explain in the last part of this paper, the connexion that may exist between the indications of the aerial electroscope, when properly settled, and many atmospheric phenomena which are daily observed without being really understood. Ashfield, near Honiton, 23rd August, 1810.

(To be continued.)

New Researches on the Properties of Electric Currents; Discontinued and directed alternately in Contrary Directions. By Professor M. A. DE LA RIVE.*

(Continued from page 47).

SECTION II.

Passage of Magnetic Electric Currents through Metallic Conductors.

I HAVE found that the magnetic electric currents are better conveyed by a heterogeneous conductor, than by a homogeneous one. I here give the experiment to which I refer for support in this opinion:-"In traversing a conductor of the same total length, that is to say a metre, but formed of two wires attached end to end, the one of iron, the other of copper, the current gave 75° (by the thermometer of Breguet); by putting in succession to each other four ends, alternately copper and iron, but always maintaining the same total length, this current indicated 76°; it gave 77° when the conductor was composed of eight ends alternately copper and iron. In each case the total length of the conductor was the same, and the copper and iron wires were always of the same diameter—a millimeter."

I immediately add, "It is probably to the circumstance that the magnetic electric currents are composed of currents discontinued and alternately contrary, that their preference for heterogeneous conductors is due; whilst that voltaic currents and thermo-electric currents continued, are always travelling in the same direction, traverse with much greater facility homogeneous conductors."

M. Lenz has made these experiments, but as I have said, with a single instantaneous current, which made the needle a galvanometer; he has not observed any difference in the intensity of the current in passing through the ends of an iron wire, and the ends of a copper wire of the same length, placed one after the other; whether these ends were alternated, or whether they were not alternated. I should not have been surprised if the author had found a contrary difference to that which I had observed: in fact, it is well known, by my own experiments and by those of M. Peltier, that the change of the conductor (when even the conductors are both metallic) is, for a current constantly travelling in the same direction, a cause of diminution. These experiments of M. Lenz prove that there is no longer a diminution when the current is instantaneous mine prove that there is a slight augmentation, when, in place of an instantaneous current, or of a continuous current, we make use of a series of instantaneous currents, alternately moving. in contrary directions, which traverses the system of solid conductors alternately between them. The first of these results, proves probably, that an instantaneous current, on account of its enormous

Archives de l'Electricité, No. 1.

force of projection, is not, like a continuous current, sensible to the small differences of conductibility which are due to the changes of solid conductors. What I have advanced is not a pure hypothesis ; for how can we explain, if we do not attribute to the same cause, the fact that an instantaneous current produces physiological effects so powerful, in spite of the great resistance which ought to be presented to it by the introduction into the totally metallic circuit of an organized body; whilst that a pile whose circuit is a far less good conductor produces such feeble results comparatively speaking? A series of discontinuous instantaneous currents ought to present the same property as an isolated current; but if these currents move alternately in a contrary direction, not only are they less sensible to the change of conductors, but these changes appear to facilitate, in a small measure, their transmission. I do not know how to see any contradiction between these results; and as to that which I have obtained, it is perhaps premature to attempt to explain it; and I have also abstained from it in my memoir. Nevertheless, I shall take occasion to show that this phenomenon presents nothing contrary to received ideas, and to indicate the cause to which it appears to me to be due; at the same time, always recognizing the fact that this subject still merits to be well studied.

A primary current instantaneously determines in a conductor which it traverses, two currents by induction; the one a, moving in a contrary direction to its own which is simultaneous with it, and which consequently diminishes a little its own intensity; the other b, moving in the same direction, and which succeeds it immediately. This current b is simultaneous with the second instantaneous current which immediately follows the first; and which moves in a contrary direction, par consequence, also in a contrary direction to the current b. This one diminishes then the intensity of the second instantaneous current: this second current in its turn determines currents by induction, which ought to produce the same effect on itself, and on the third instantaneous current; and so of the rest. It results then from that which precedes, that a series of instantaneous currents travelling in alternative contrary directions through a conductor, determine currents by induction in this conductor, which diminish their original intensity. All that will enfeeble these currents by induction, will as much augment the intensity of the fundamental currents: now, this weakening, we may produce by disposing the metallic wire in such a fashion that the ends of iron and copper, of which it is composed, are alternated as much as possible; this disposition, in fact, enfeebles excessively the induction of the current on itself, which is, as we know, as much stronger as the homogeneous conductor in which it takes place is increased in length.

Such is then the explication which appears to me the most natural of the phenomenon which I have observed, and which as we see proceeds from the fact that the currents with which I have obtained

it are instantaneous, and which move alternately in contrary directions.

SECTION III.

On the Passage of Magneto-Electric Currents through Liquid Conductors.

M. Lenz studied in detail the paragraph in which I was occupied on the passages of magneto-electric currents through liquid conductors. He believes, as I do, that the influence which the length more or less great of the liquid conductor exercises on the intensity of the transmitted electricity, is greater for these currents than for magneto-electric currents: he remarks that it is a consequence quite natural of the law of Ohm. I do not deny it, for here you will see what I add after having reported my results.

"I do not endeavour to seek in the preceding tables the following law which the intensity of the current augments in proportion as the distance is diminished; this law, in fact, is connected, as will be shown, of the beautiful works of M. M. Ohm and Fechner, with the conductibility of the whole of the circuit which the currents traverse, and consequently, in this case, with that of the metallic wire in which it is developed, and of the helix which it traverses, &c."

M. Lenz is no longer in agreement with me when he attempts to appreciate the influence which is exercised on the intensity of magneto-electric currents by the interposition of a metallic diaphragm in the liquid which the currents traverse. I have remarked that, if this diaphragm has an extent equal to that of the section of the liquid in which it is placed, the magneto-electrical currents do not undergo any loss of intensity, because we do not charge the length of liquid traversed; whilst that, in the same circumstances, the voltaic and thermo-electric currents undergo a sensible diminution. M. Lenz concludes, either from experiments which he had made precedingly, or from new ones which he has made in the same circumstances as mine, that is to say, by interposing a plate of platinum in a diluted acid, that an instantaneous current will undergo a considerable diminution of intensity by the effect of the interposition of a metallic diaphragm in the liquid conductor. He finds even that the resistance which the column undergoes in its passage across the plate, is nearly ten times as great as that which it meets with in traversing the entire body of liquid.

I am ready to recognise the exactness of the result obtained by M. Lenz, but I do not conclude from it that mine are erroneous. In fact, our experiments are not comparable: since in the one a single instantaneous current is made use of, and in the other a series of instantaneous currents is employed, alternately travelling in contrary directions. It is true that the nature of the circuit, quite metallic, in which the magneto-electric currents are developed, ought to render them much more sensible than the hydro-electric cur