nt, and
whilst engaged in investigating the point, we may admit, what is the fact,
that the forces are of higher intensity at the surfaces of the smaller
balls than at those of the larger (1372. 1374.); that the former,
therefore, determine the discharge, by first rising up to that exalted
condition which is necessary for it; and that, whether brought to this
condition by induction towards the walls of a room or the large balls I
have used, these may fairly be compared one with the other in their
influence and actions.

1501. The conclusions I arrive at are: first, that when two equal small
conducting surfaces equally placed in air are electrified, one positively
and the other negatively, that which is negative can discharge to the air
at a tension a little lower than that required for the positive ball:
second, that when discharge does take place, much more passes at each time
from the positive than from the negative surface (1491.). The last
conclusion is very abundantly proved by the optical analysis of the
positive and negative brushes already described (1468.), the latter set of
discharges being found to recur five or six times oftener than the
former[A].

[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
mod