_p_, or any small
surface, as the rounded end of a rod, when it is opposed to a large
surface, as that of a ball or plate, rather than to another point or end,
the distance being in both cases the same, fall into harmonious relation
with my theory (1302.). For in the latter case, the small surface _p_ is
affected only by those particles which are brought into the inductive
condition by the equally small surface of the opposed conductor, whereas
when that is a ball or plate the lines of inductive force from the latter
are concentrated, as it were, upon the end _p_. Now though the molecules of
the dielectric against the large surface may have a much lower state of
tension than those against the corresponding smaller surface, yet they are
also far more numerous, and, as the lines of inductive force converge
towards a point, are able to communicate to the particles contained in any
cross section (1369.) nearer the small surface an amount of tension equal
to their own, and consequently much higher for each individual particle; so
that, at the surface of the smaller conductor, the tension of a particle
rises much, and if that conductor were to terminate in a point, the tension
would rise to an infinite degree, except that it is limited, as before
(1368.), by discharge. The nature of the discharge from small surfaces and
points under induction will be resumed hereafter (1425. &c.)

1375. _Rarefaction_ of the air does not alter the _intensity_ of inductive
action (1284. 1287.); nor is there any reason, as far as I can perceive,
why it should. If the quantity of electricity and the distance remain the
same, and the air be rarefied one-half, then, though one-half of the
particles of the dielectric are removed, the other half assume a double
degree of tension in their polarity, and therefore the inductive forces are
balanced, and the result remains unaltered as long as the induction and
insulation are sustained. But the case of _discharge_ is very different;
for as there are only half the number of dielectric particles in the
rarefied atmosphere, so these are brought up to the discharging intensity
by half the former quantity of electricity; discharge, therefore, ensues,
and such a consequence of the theory is in perfect accordance with Mr.
Harris's results (1365.).

1376. The _increase_ of electricity required to cause discharge over the
same distance, when the pressure of the air or its density is increased,
flows in a similar