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must have been negative electrical to the atmosphere, prior to their receiving their respective charges from it; and as those electric charges were not communicated to the wires prior to their ascent, it is obvious, also, that they were received from those portions of air through which they ascended, and eventually from those regions which were invaded by their highest points. And since the elec

tric charges are found to be the highest from the highest altitudes the electric pressure is also greater in those places : hence the exploring wires become electro-polar, having their lower and upper parts, positive and negative respectively. And since the circumambient pressure at the lower ends of the wires is uniform, the electric state which each wire displays will depend on the electric state of the air surrounding its highest point; and consequently, the relative electric actions exhibited by the lower ends of the kite strings are true representatives of the relative electric conditions of those strata of air in which the kites were floating.

The same fact may be proved by the opposite process. If, for instance, from a balloon at a great altitude, several insulated wires of different lengths, were to be let down by weighting the lower extremities, each wire would be found negative electrical with respect to the balloon itself, and consequently with respect to its contents and the surrounding air. The shortest wire, in this case, would be the least electrical, and the longest one the most electrical in the series, and every one in the series would be negative electrical on some function of its length, no two of them being alike. Hence, if the longest wire touched the ground, it would be negative to the whole of the remaining part of the series.' By this process, as decidedly as by that with the kites, the wires would become electro-polar; and because the lower extremities of all the wires would be subjected to a less degree of electric pressure than that investing their upper extremities; the lower pole of each wire would be electro-positive. The polar action, however, would be of different degrees of intensity, and consequently, the lower ends of the wires would relatively display different electric states ; being positive and negative throughout the series. The lowermost wire (if insulated from the ground) being positive, and the uppermost one negative to all the rest. Hence we understand, that it is a matter of no consequence whether the wires proceed from one common station downwards, or from one common station upwards, they will, in either case, be relatively positive and negative accordingly with their respective lengths, when in a vertical position.

Again, since the different degrees of polarity, or different electric states of the extremities of the wires, depend upon different degrees of electric pressure at the upper and lower statious, it is obvious that if the pressure was equal from one end of the wire to the other, no electro-polarity could possibly take place. Moreover, since no electric discharge can possibly happen independently of polarity, we learn the reason why balloons have passed with impunity through dense clouds highly charged with the electric inatter (thunder clouds), not experiencing even the slightest indication of electric action ; excepting, perhaps, the unpleasant sensation which the aeronaut might experience from the great circumambient electric pressure.

It is to the same cause that the 'want of action was discernable by the Scrutator in the interior of Beccaria's electrical well, and by Dr. Faraday whilst living in an electrical cage. Both were surrounded by equable electric pressures, and consequently where no electric phenomena could happen.

I have already informed you, that the quantity of electric matter in bodies generally, is almost continually varying, from the evervarying surrounding electric pressure; and that different bodies have different degrees of susceptibility for the reception of the electric Auid. Hence it will be easy to conceive that any insulated body of great dimensions, would receive a greater quantity of the electric fuid than a small one of the same kind, when both were under the same degree of pressure. Hence it is, that a long insulated copper wire stretched horizontally at the height of a few yards from the ground, will, occasionally, even when no cloud is present, receive a considerable charge, sufficient, indeed, to communicate powerful shocks, from the surrounding air; although a very short piece of the same wire, would never receive an appreciable charge under any circumstance of surrounding pressure in a cloudless sky. But it must be observed, that such a wire being surrounded by an equable electric pressure, cannot possibly become electro-polar, and consequently, could not dispose of any of its charge to a vicipal insulated wire of the same kind, whether the lengths were equal or unequal; unless, indeed, the latter wire had not been exposed to the same pressure for a sufficient period of time, to receive all the fluid due to its susceptibility of being charged with from that pressure.

Now, although no wire could dispose of any part of such a natu ral charge of the electric fluid to another of the same kind and similarly situated, the distribution of its fluid would suffer a change by the approach of the other wire in certain manners. If, for instance, the two wires approached one another longitudinally, until they came close together, and laid side by side from one end to the other. Under these circumstances, the fluid previously occupying those parts of the two surfaces, which, after contact, forms the plane of contact of the wires, would become displaced by mutual repulsion; and after a moment's disturbance of the whole of the Auid in both wires, a new distribution and electro-equilibrium would be established.

With respect to the approach of insulated matter of other kinds, to that constituting the insulated wire, it is obvious that electrical pehenomena would be displayed in consequence of a difference of electric pressures which the bodies would exercise on each other as the surfaces approach. If the approaching body were uninsulated, a polarization would take place, whatever were the character of that body ; because the electric pressure on the wire would be lessened at, and about the point approached: it would there exhibit a positive pole; and if the body approached near enough, a discharge from the wire would take place, the force of which would be proportional to the extent of the wire and the electric pressure of the surrounding aerial medium at that time; and as that pressure is continually varying, the charge in the wire will vary also. Therefore the same wire cannot be charged to the same extent at all times, which is a fact well ascertained by several electricians of the highest repute. From the whole of these circumstances, a long insulated wire appears to he well adapted for an important part of an electro-phorascope, which would indicate the changes of electric pressure in the lower strata of the atmosphere, under a cloudless sky; and as such a wire would always represent the electrical state of that stratum of air in which it was suspended, it would also form an important part of an electro-metaboliascope, which would indicate those changes from plus 10 minus, and vice versa, of the air, with respect to the earth, which occasionally take place by the approach, transit, and departure of clouds.

On the Induction from the Discharge of the Battery.

By M. Ch. Matteucci.*

When I undertook the study of the secondary current developed by induction, by means of a current from the Leyden jar, I took as a measure of the direction and of intensity of this current, the degree and direction of the magnetism which it developes in a steel needle which is contained in a cylindrical spiral dextrorsum traversed by this current of induction.". M. Henry and M. Marianini, who were occupied at the same time in the study of this phenomenon, have employed the same means; M. Marianini alone made use of temporary magnetism. Without knowing the works of each other, we have published our results, and they are found to agree perfectly. These results may be reduced to the following:- Firstly: If the discharge is feeble, the secondary current is directed in an inverse direction to the current of the jar: in all other cases it has the same direction as the latter. Secondly: If the two currents are removed from each other, we always arrive at a certain distance at which the secondary current is found to be reversed. Thirdly: Any intermediate metallic plates destroy the secondary current by beginning to produce it in an inverse direction, and at the same time the secondary current travelling in the same direction as that of the jar, traverses the plate. M. Reiss has also studied this same subject, making use of a thermoscope to measure the intensity of the secondary current. He obtained some remarkable results, which may in some measure he resolved into those which we obtained. This philosopher accuses

Archives De L'Ectricité. No. I.

the process which we employed to determine the direction of the current, of uncertainty, in referring to the beautiful work of M. Savary, which proves how the direction and the degree of magnetization are variable in circumstances which have not yet been subjected to any general law.

Since my first researches I have reflected a good deal on the results of M. Savary; and it will be seen in my memoir, that by employing very feeble discharges and very long circuits, I have endeavoured to place myself in conditions in which the magnetic action of the current no longer presents anomalies. I persist in believing that the indication of magnetism is always correct for measuring the intensity and the direction of the current. I hope that ere long it will not fail to be proved. I believe this process to be more sensitive than all the others which we have employed, and capable of indicating to us, in the duration and force of the current, many variations which escape other methods. I have at all times been desirous of trying if the galvanometer might be employed in these researches; I have taken for this, Gourjon's galvanometer, such as Mellopi employed in his researches on heat. I have always employed my two spiral planes, each of which is composed of twenty-three metres of copper wire. These two spirals are brought very near to each other, and are only separated by a plate of very thin glass. It is with this apparatus that I have obtained for the first time very brilliant sparks of induction, by employing one of the smallest Leyden jars that can be made with a smelling bottle. I soon perceived that, in order to have signs from the galvanometer, it would be necessary to employ a battery. The batteries that I have employed consisted of 4, 8, 10, or 12 jars, and had 0 m.C., 3864, 0 m. c., 6328,0 m.c., 9660, 2 m. c, 152, of coated surface.

Before detailing the results which I obtained, I confess that, particularly with charges of a very slight degree of tension, I have always seen a spak escape in the circuit of the galvanometer. It would have been necessary to employ a galvavometer the wire of which was well covered with varnish, like those of Colladen. I obtained very constant numbers, but I still refrain from giving them as invariable, and as establishing a law numerically expressed. The spark which is given out in the circuit of the galvanometer ought always to destroy a portion of the action of the current, and this portion ought to be variable in each case. With a battery of twelve jars I have obtained the following numbers :

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The direction of the secondary current is always the same as that of the current of the jar, which gues from the surface which communi

40

7 ex.

cates with the conductor of the machine, to the other which communicates with the ground. Moreover, if we charge this battery up to the point where we perceive the noise of the spontaneous discharge, the needle of the galvanometer is pushed on to 90°. I have compared the effects of two batteries of four and of eight bottles, for the same degree of tension, and I obtained for the secondary currents the following numbers :

Tension. With 4 bottles. With 8 bottles.
10°

. 3o
20

4 ex.
30
40
50
10

16 The direction being still the same as in the preceding case. We see clearly that the intensity of the secondary current increases with the tension and with the quantity of electricity which is discharged through the primitive circuit. If we make the distance between the two spirals to vary, the secondary current does not change its direction; it becomes enfeebled with rapidity, and is reduced to zero; but we never obtain an inverse current, as is indicated by the process of magnetizing employed with very feeble discharges. Here are some of the numbers; the charge was from eight jars, and constantly at 400 of tension :Distance between the two spirals. Deflection of the galvanometer. om., 003

170
0,01

9 ex.
0,02
0,06
0 , 12

Zero. In order to establish the law which ought to connect the direction of this secondary current of the Leyden jar with the effects of voltaic induction discovered by Faraday, I have attempted to multiply the number of spirals, in order to oblige the secondary current to become primitive in another circuit. The experiment succeeded very easily. I constructed three pairs of spiral planes of the same copper wire, and of the same length as the two preceding spirals. This is a very remarkable experiment of uniting the functions of these three pairs of spirals in such a manner as to obtain the spark. The disposition of the experiment is very simple: we add to the second spiral—that is to say, to that in which the primary induction takes place--another spiral, and at a certain distance. A fourth spiral is placed like the second and the first, in face of the third. To this fourth spiral we again add a fifth, and in face of this latter we put as for the second and third, a sixth spiral. We dispose the circuit in such a manner that there is an interruption in the circuit of the second and third, another in that of the fourth and fifth, and then a latter one in that of the sixth. It is sufficient if we cause to pass the discharge from

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