In applying himself to inquiries of this kind, Mr Hermann of Berlin has made this very curious obser vation, that the conducting faculty of certain bodies for the'two electricities is unequal ; so that by atte nuating more and more the repulsive force, we ob tain a limit where the body becomes insulating as to the one electricity, while it still remains a con ductor of the other. This is proved by the experi ments which we are now to relate.
Mr Hermann insulated an electromotive apparatus, constructed with a good liquid conductor, such, for example, as the solution of the muriate of soda. He made each of its poles communicate with a very sen sible gold leaf electrometer, equally well insulated. The leaves of each of the electrometers soon acquir ed the degree of 'divergence determined by the num ber of plates, and the electrical zero was found in the middle of the apparatus.
This being done, he took a prism of alkaline soap, and inserted in one of its ends a metallic wire com municating with the ground. He then touched with the other end, any one of the poles of the pile, and this pale wia immediately discharged. The divergence of the electrometer was reduced to nothing, and the electrometer of the other pole diverged more than be. fore. Everything happened as if the pole, which was touched by the prism, had communicated with the ground, and the soap seemed to act as a conductor to either electricity indifferently.
The pile remaining always insulated, and the re pulsive influences of its poles being restored, he made these poles now to communicate together through the medium of the same prism of soap, by inserting into the two ends of it the metallic-wires proceeding from each pole. In spite of this communication, the two electrometers continued to diverge as before, so that the soap now seemed to act as a non-conduct ing body.
But when this insulation was distinctly recogniz ed, he touched, for an instant, the soap with a wire of metal which communicated with the ground. Im mediately the resinous pole was neutralized, and the repulsive force of the vitreous pole attained its maxi mum. Thus, the soap assumes anew its conduct ing faculty, but only to allow the efflux of therre sinous electricity, which it always transmitted in pre ference. Even if we touch it quite near to the wire, which proceeds from the vitreous pole of the pile, this pole remains no less insulated on this account.
The flame of alcohol presented to Mr Hermann similar effects, but the conducting disposition was in favour of the vitreous electricity. All this, however, only refers to very slight degrees of electricity, such as the electromotive apparatus affords ; for both the flame of alcohol and soap conduct, imperfectly no doubt, but in a manner sensibly equal, more power. ful degrees of electricity.
By repeating these experiments, Mr Biot recop nixed a property in sulphuric ether, which cont. pletes those discoveries of Mr Hermann. This quid, interposed between the two poles of the pile, seems to insulate them Like soap and the flame of alco hol. If we place it in the circuit of the apparatus for decomposing water, it will not•isengage any bubbles of gas. And, in fine, all the signs of the insulation of the two poles make their appearance. But if we touch the ether for a single instant with a metallic wire, to snake it communicate with the ground, ap. plying, at the same time, a condenser to any of the wires of the pile, this condenser will be ly charged, as if the ether had all of a sudden be came a conductor of the electricity belonging to the pole to which the condenser is applied. In describing these experiments, we have said that the two poles of the pile seem to be insulated by the interposition of a prism of alkaline soap. The insulation is, in fact, only partial ; the motion of the electricity in the prism of soap is not alto gether extinguished ; it is only slower than in the pile itself, which allows the latter to be sensibly re charged, and to acquire a tension at its poles, while the soap is discharging it. In proof of this, it may be observed, that the same prism of soap conducts absolutely the whole electricity of a less conducting pile, such as that with paste; it takes away all ten. sion from its poles, and the condenser is hence•no more• charged in touching them. The flame of el.
cohol interposed between the poles of this same pile does not discharge it completely ; it leaves a tension remaining at its poles, and we can repeat with it the experiments of Mr Hermann. This flame, then, does not conduct the electricity so well as the alka line soap.