These excentricities which are now quite large, have then always been and will always remain large.

2. The same is true of the inclination of their orbits. So that the amount of excentricity and inclination answers to the primitive conditions of the formation of the group.

3. These propositions are true only for distances from the sun above 200. An asteroid situated between Mars and the distance of about 2.00 would not be stable in the meaning which is attached to that word in celestial mechanics.

Flora, which is nearest to the sun of the known asteroids, is 2.20 distant. The author observes that it is quite remarkable that a planet has been found almost up to the line which theory assigns as the limit of stability, and that none have been found beyond it. Must we believe that the same cause which has given origin to so many asteroids above the distance 2.00 has also distributed them below this distance? but that, the excentricities and inclinations of these last being considerably increased, it is at present difficult to discover them, especially because towards their perihelion, they will be immersed in the light of the sun, and that coming to their opposition only near their aphelia, they will then be too far from us?

4. Owing to the magnitude of the excentricities and the inclinations and the smallness of their variations, the mean motions of the perihelia and of the nodes are proportional to the times.

ART. XIII.-On Electric Induction-Associated cases of Current and Static Effects; by Professor FARADAY, D.C.L., F.R.S.*

CERTAIN phenomena that have presented themselves in the course of the extraordinary expansion which the works of the Electric Telegraph Company have undergone, appeared to me to offer remarkable illustrations of some fundamental principles of electricity, and strong confirmation of the truthfulness of the view which I put forth sixteen years ago, respecting the mutually dependent nature of induction, conduction, and insulation (Experimental Researches, 1318, &c.). I am deeply indebted to the Company, to the Gutta Percha Works, and to Mr. Latimer Clarke, for the facts; and also for the opportunity both of seeing and showing them well.

Copper wire is perfectly covered with gutta percha at the Company's works, the metal and the covering being in every part regular and concentric. The covered wire is usually made into half-mile lengths, the necessary junctions being effected by twisting or binding, and ultimately soldering; after which the place

*Phil. Mag., 4th Ser., vii, 197, March, 1854.

is covered with fine gutta percha, in such a manner as to make the coating as perfect there as elsewhere: the perfection of the whole operation is finally tried in the following striking manner by Mr. Statham, the manager of the works. The half-mile coils are suspended from the sides of barges floating in a canal, so that the coils are immersed in the water whilst the two ends of each coil rise into the air: as many as 200 coils are thus immersed at once; and when their ends are connected in series, one great length of 100 miles of submerged wire is produced, the two extremities of which can be brought into a room for experiment. An insulated voltaic battery of many pairs of zinc and copper, with dilute sulphuric acid, has one end connected with the earth, and the other, through a galvanometer, with either end of the submerged wire. Passing by the first effect, and continuing the contact, it is evident that the battery current can take advantage of the whole accumulated conduction or defective insulation in the 100 miles of gutta percha on the wire, and that whatever portion of electricity passes through to the water will be shown by the galvanometer. Now the battery is made one of intensity, in order to raise the character of the proof, and the galvanometer employed is of considerable delicacy; yet so high is the insulation, that the deflection is not more than 50. As another test of the perfect state of the wire, when the two ends of the battery are connected with the two ends of the wire, there is a powerful current of electricity shown by a much coarser instrument; but when any one junction in the course of the 100 miles is separated, the current is stopped, and the leak or deficiency of insulation rendered as small as before. The perfection and condition of the wire may be judged of by these facts:

The 100 miles, by means of which I saw the phenomena, were thus good as to insulation. The copper wire was th of an inch in diameter; the covered wire was 4ths; some was a little less, being nds in diameter; the gutta percha on the metal may therefore be considered as 0·1 of an inch in thickness. 100 miles of like covered wire in coils were heaped up on the floor of a dry warehouse and connected in one series, for comparison with that under water.

Consider now an insulated battery of 360 pairs of plates (4×3 inches) having one extremity to the earth; the water wire with both its insulated ends in the room, and a good earth discharge wire ready for the requisite communication: when the free battery end was placed in contact with the water wire and then removed, and afterwards a person touching the earth discharge touched also the wire, he received a powerful shock. The shock was rather that of a voltaic than of a Leyden battery; it occupied time, and by quick tapping touches could be divided into numerous small shocks; I obtained as many as forty sensible

shocks from one charge of the wire. If time were allowed to intervene between the charge and discharge of the wire, the shock was less; but it was sensible after two, three, or four minutes, or even a longer period.

When, after the wire had been in contact with the battery, it was placed in contact with a Statham's fuse, it ignited the fuse (or even six fuses in succession) vividly; it could unite the fuse three or four seconds after separation from the battery. When, having been in contact with the battery, it was separated and placed in contact with a galvanometer, it affected the instrument very powerfully; it acted on it, though less powerfully, after the lapse of four or five minutes, and even affected it sensibly twenty or thirty minutes after it had been separated from the battery. When the insulated galvanometer was permanently attached to the end of the water wire, and the battery pole was brought in contact with the free end of the instrument, it was most instructive to see the great rush of electricity into the wire; yet after that was over, though the contact was continued, the deflection was not more than 50, so high was the insulation. Then separating the battery from the galvanometer, and touching the latter with the earth wire, it was just as striking to see the electricity rush out of the wire, holding for a time the magnet of the instru ment in the reverse direction to that due to the ingress or charge.

These effects were produced equally well with either pole of the battery or with either end of the wire; and whether the electric condition was conferred and withdrawn at the same end, or at the opposite ends of the 100 miles, made no difference in the results. An intensity battery was required, for reasons which will be very evident in the sequel. That employed was able to decompose only a very small quantity of water in a given time. A Grove's battery of eight or ten pairs of plates, which would have far surpassed it in this respect, would have had scarcely a sensible power in affecting the wire.

When the 100 miles of wire in the air were experimented with in like manner, not the slightest signs of any of these effects were produced. There is reason, from principle, to believe that an infinitesimal result is obtainable, but as compared to the water wire the action was nothing. Yet the wire was equally well and better insulated, and as regarded a constant current, it was an equally good conductor. This point was ascertained by attaching the end of the water wire to one galvanometer, and the end of the air wire to another like instrument; the two other ends of the wires were fastened together, and to the earth contact; the two free galvanometer ends were fastened together, and to the free pole of the battery: in this manner the current was divided between the air and water wires, but the galvanometers were affected to precisely the same amount. To make the result more

certain, these instruments were changed one for the other, but the deviations were still alike; so that the two wires conducted with equal facility.

The cause of the first results is, upon consideration, evident enough. In consequence of the perfection of the workmanship, a Leyden arrangement is produced upon a large scale; the copper wire becomes charged statically with that electricity which the pole of the battery connected with it can supply ;* it acts by induction through the gutta percha (without which induction it could not itself become charged, Exp. Res. 1177), producing the opposite state on the surface of the water touching the gutta percha, which forms the outer coating of this curious arrangement. The gutta percha across which the induction occurs is only 0.1 of an inch thick, and the extent of the coating is enormous. The surface of the copper wire is nearly 8300 square feet, and the surface of the outer coating of water is four times that amount, or 33,000 square feet; hence the striking character of the results. The intensity of the static charge acquired is only equal to the intensity at the pole of the battery whence it is derived; but its quantity is enormous, because of the immense extent of the Leyden arrangement; and hence when the wire is separated from the battery and the charge employed, it has all the powers of a considerable voltaic current, and gives results which the best ordinary electric machines and Leyden arrangements cannot as yet approach.

That the air wire produces none of these effects is simply because there is no outer coating correspondent to the water, or only one so far removed as to allow of no sensible induction, and therefore the inner wire cannot become charged. In the air wire of the warehouse, the floor, walls, and ceiling of the place constituted the outer coating, and this was at a considerable distance; and in any case could only affect the outside portions of the coils of wire. I understand that 100 miles of wire, stretched in a line through the air so as to have its whole extent opposed to earth, is equally inefficient in showing the effects, and there it must be the distance of the inductric and inducteous surfaces (1483), combined with the lower specific inductive capacity of air, as compared with gutta percha, which causes the negative result. The phenomena altogether offer a beautiful case of the identity of static and dynamic electricity. The whole power of a considerable battery may in this way be worked off in separate portions, and measured out in units of static force, and yet be employed afterwards for any or every purpose of voltaic electricity.

I now proceed to further consequences of associated static and dynamic effects. Wires covered with gutta percha and then inclosed in tubes of lead or of iron, or buried in the earth, or sunk

* Davy, Elements of Chemical Philosophy, p. 154.

in the sea, exhibit the same phenomena as those described, the like static inductive action being in all these cases permitted by the conditions. Such subterraneous wires exist between London and Manchester; and when they are all connected together so as to make one series, offer above 1500 miles; which, as the duplications return to London, can be observed by one experimenter at intervals of about 400 miles, by the introduction of galvanometers at these returns. This wire, or the half or fourth of it, presented all the phenomena already described; the only difference was, that as the insulation was not so perfect, the charged condition fell more rapidly. Consider 750 miles of the wire in one length, a galvanometer a being at the beginning of the wire, a second galvanometer b in the middle, and a third c at the end; these three galvanometers being in the room with the experimenter, and the third c perfectly connected with the earth. On bringing the pole of the battery into contact with the wire through the galvanometer a, that instrument was instantly affected; after a sensible time b was affected, and after a still longer time c: when the whole 1500 miles were included, it required two seconds for the electric stream to reach the last instrument. Again; all the instruments being deflected (of course not equally, because of the electric leakage along the line), if the battery were cut off at a, that instrument instantly fell to zero; but b did not fall until a little while after; and c only after a still longer interval, a current flowing on to the end of the wire whilst there was none flowing in at the beginning. Again; by a short touch of the battery pole against a, it could be deflected and could fall back into its neutral condition before the electric power had reached b; which in its turn would be for an instant affected, and then left neutral before the power had reached c; a wave of force having been sent into the wire which gradually travelled along it, and made itself evident at successive intervals of time in different parts of the wire. It was even possible, by adjusted touches of the battery, to have two simultaneous waves in the wire following each other, so that at the same moment that c was affected by the first wave, a or b was affected by the second; and there is no doubt that by the multiplication of instruments and close attention, four or five waves might be obtained at once.

If after making and breaking battery contact at a, a be immediately connected with the earth, then additional interesting effects occur. Part of the electricity which is in the wire will return, and passing through a will deflect it in the reverse direction; so that currents will flow out of both extremities of the wire in opposite directions, whilst no current is going into it from any source. Or if a be quickly put to the battery and then to the earth, it will show a current first entering into the wire, and