[A] A very excellent mode of examining the relation of small positive
  and negative surfaces would be by the use of drops of gum water,
  solutions, or other liquids.  See onwards (1581. 1593.).

1502.  If, now, a small ball be made to give brushes or brushy sparks by a powerful machine, we can, in some measure, understand and relate the difference perceived when it is rendered positive or negative.  It is known to give when positive a much larger and more powerful spark than when negative, and with greater facility (1482.):  in fact, the spark, although it takes away so much more electricity at once, commences at a tension higher only in a small degree, if at all.  On the other hand, if rendered negative, though discharge may commence at a lower degree, it continues but for a very short period, very little electricity passing away each time.  These circumstances are directly related; for the extent to which the positive spark can reach, and the size and extent of the positive brush, are consequences of the capability which exists of much electricity passing off at one discharge from the positive surface (1468. 1501.).

1503.  But to refer these effects only to the form and size of the conductor, would, according to my notion of induction, be a very imperfect mode of viewing the whole question (1523. 1600.).  I apprehend that the effects are due altogether to the mode in which the particles of the interposed dielectric polarize, and I have already given some experimental indications of the differences presented by different electrics in this respect (1475. 1476.).  The modes of polarization, as I shall have occasion hereafter to show, may be very diverse in different dielectrics.  With respect to common air, what seems to be the consequence of a superiority in the positive force at the surface of the small ball, may be due to the more exalted condition of the negative polarity of the particles of air, or of the nitrogen in it (the negative part being, perhaps, more compressed, whilst the positive part is more diffuse, or vice versa (1687. &c.)); for such a condition could determine certain effects at the positive ball which would not take place to the same degree at the negative ball, just as well as if the positive ball had possessed some special and independent power of its own.

1504.  The opinion, that the effects are more likely to be dependent upon the dielectric than the ball, is supported by the character of the two discharges.  If a small positive ball be throwing off brushes with ramifications ten inches long, how can the ball affect that part of a ramification which is five inches from it?  Yet the portion beyond that place has the same character as that preceding it, and no doubt has that character impressed by the same general principle and law.  Looking upon the action of the contiguous particles of a dielectric as fully proved, I see, in such a ramification, a propagation of discharge from particle to particle, each doing for the one next it what was done for it by the preceding particle, and what was done for the first particle by the charged metal against which it was situated.