Part 37 (1/2)

. . . . 0 215 . . . .

204 . . . .

Charge divided.

. . . . 118 118 . . . .

. . . . 0 after being discharged.

0 . . . . after being discharged.

1261. Here 204 must be the utmost of the divisible charge. The app. i. and app. ii. present 118 as their respective forces; both now much _above_ the half of the first force, or 102, whereas in the former case they were below it. The lac app. i. has lost only 86, yet it has given to the air app. ii. 118, so that the lac still appears much to surpa.s.s the air, the capacity of the lac app. i. to the air app. ii. being as 1.37 to 1.

1262. The difference of 1.55 and 1.37 as the expression of the capacity for the induction of sh.e.l.l-lac seems considerable, but is in reality very admissible under the circ.u.mstances, for both are in error in _contrary directions_. Thus in the last experiment the charge fell from 215 to 204 by the joint effects of dissipation and absorption (1192. 1250.), during the time which elapsed in the electrometer operations, between the applications of the carrier ball required to give those two results. Nearly an equal time must have elapsed between the application of the carrier which gave the 204 result, and the division of the charge between the two apparatus; and as the fall in force progressively decreases in amount (1192.), if in this case it be taken at 6 only, it will reduce the whole transferable charge at the time of division to 198 instead of 204; this diminishes the loss of the sh.e.l.l-lac charge to 80 instead of 86; and then the expression of specific capacity for it is increased, and, instead of 1.37, is 1.47 times that of air.

1263. Applying the same correction to the former experiment in which air was _first_ charged, the result is of the _contrary_ kind. No sh.e.l.l-lac hemisphere was then in the apparatus, and therefore the loss would be princ.i.p.ally from dissipation, and not from absorption: hence it would be nearer to the degree of loss shown by the numbers 304 and 297, and being a.s.sumed as 6 would reduce the divisible charge to 284. In that case the air would have lost 170, and communicated only 113 to the sh.e.l.l-lac; and the relative specific capacity of the latter would appear to be 1.50, which is very little indeed removed from 1.47, the expression given by the second experiment when corrected in the same way.

1264. The sh.e.l.l-lac was then removed from app. i. and put into app. ii. and the experiments of division again made. I give the results, because I think the importance of the point justifies and even requires them.

App. i. Air. App. ii. Lac.

b.a.l.l.s 200.

. . . . 0.

286 . . . .

283 . . . .

Charge divided.

. . . . 110 109 . . . .

. . . . 0.25 after discharge.

Trace . . . . after discharge.

Here app. i. retained 109, having lost 174 in communicating 110 to app.

ii.; and the capacity of the air app. is to the lac app., therefore, as 1 to 1.58. If the divided charge be corrected for an a.s.sumed loss of only 3, being the amount of previous loss in the same time, it will make the capacity of the sh.e.l.l-lac app. 1.55 only.

1265. Then app. ii. was charged, and the charge divided thus:

App. i. Air. App. ii. Lac, 0 . . . .

. . . . 250 . . . . 251 Charge divided.

146 . . . .

. . . . 149 a little . . . . after discharge.

. . . . a little after discharge.

Here app. i. acquired a charge of 146, while app. ii. lost only 102 in communicating that amount of force; the capacities being, therefore, to each other as 1 to 1.43. If the whole transferable charge be corrected for a loss of 4 previous to division, it gives the expression of l.49 for the capacity of the sh.e.l.l-lac apparatus.

1266. These four expressions of 1.47, 1.50, 1.55, and 1.49 for the power of the sh.e.l.l-lac apparatus, through the different variations of the experiment, are very near to each other; the average is close upon 1.5, which may hereafter be used as the expression of the result. It is a very important result; and, showing for this particular piece of sh.e.l.l-lac a decided superiority over air in allowing or causing the act of induction, it proved the growing necessity of a more close and rigid examination of the whole question.

1267. The sh.e.l.l-lac was of the best quality, and had been carefully selected and cleaned; but as the action of any conducting particles in it would tend, virtually, to diminish the quant.i.ty or thickness of the dielectric used, and produce effects as if the two inducing surfaces of the conductors in that apparatus were nearer together than in the one with air only, I prepared another sh.e.l.l-lac hemisphere, of which the material had been dissolved in strong spirit of wine, the solution filtered, and then carefully evaporated. This is not an easy operation, for it is difficult to drive off the last portions of alcohol without injuring the lac by the heat applied; and unless they be dissipated, the substance left conducts too well to be used in these experiments. I prepared two hemispheres this way, one of them unexceptionable; and with it I repeated the former experiments with all precautions. The results were exactly of the same kind; the following expressions for the capacity of the sh.e.l.l-lac apparatus, whether it were app. i. or ii., being given directly by the experiments, 1.46, 1.50, 1.52, 1.51; the average of these and several others being very nearly 1.5.

1268. As a final check upon the general conclusion, I then actually brought the surfaces of the air apparatus, corresponding to the place of the sh.e.l.l-lac in its apparatus, nearer together, by putting a metallic lining into the lower hemisphere of the one not containing the lac (1213.). The distance of the metal surface from the carrier ball was in this way diminished from 0.62 of an inch to 0.435 of an inch, whilst the interval occupied by the lac in the other apparatus remained O.62 of an inch as before. Notwithstanding this change, the lac apparatus showed its former superiority; and whether it or the air apparatus was charged first, the capacity of the lac apparatus to the air apparatus was by the experimental results as 1.45 to 1.

1269. From all the experiments I have made, and their constant results, I cannot resist the conclusion that sh.e.l.l-lac does exhibit a case of _specific inductive capacity_. I have tried to check the trials in every way, and if not remove, at least estimate, every source of error. That the final result is not due to common conduction is shown by the capability of the apparatus to retain the communicated charge; that it is not due to the conductive power of inclosed small particles, by which they could acquire a polarized condition as conductors, is shown by the effects of the sh.e.l.l-lac purified by alcohol; and, that it is not due to any influence of the charged state, formerly described (1250.), first absorbing and then evolving electricity, is indicated by the _instantaneous_ a.s.sumption and discharge of those portions of the power which are concerned in the phenomena, that instantaneous effect occurring in these cases, as in all others of ordinary induction, by charged conductors. The latter argument is the more striking in the case where the air apparatus is employed to divide the charge with the lac apparatus, for it obtains its portion of electricity in an _instant_, and yet is charged far above the _mean_.