t was
approximated caused the size and sound of the negative brush to diminish,
and, at last, to cease, leaving the negative end silent and dark, yet
effective as to discharge.

1470. When the round end of a smaller wire (fig. 123.) was advanced towards
the negative brush, it (becoming positive by induction) exhibited the quiet
glow at 8 inches distance, the negative brush continuing. When nearer, the
pitch of the sound of the negative brush rose, indicating quicker
intermittences (1431.); still nearer, the positive end threw off
ramifications and distinct brushes; at the same time, the negative brush
contracted in its lateral directions and collected together, giving a
peculiar narrow longish brush, in shape like a hair pencil, the two brushes
existing at once, but very different in their form and appearance, and
especially in the more rapid recurrence of the negative discharges than of
the positive. On using a smaller positive wire for the same experiment, the
glow first appeared on it, and then the brush, the negative brush being
affected at the same time; and the two at one distance became exceedingly
alike in appearance, and the sounds, I thought, were in unison; at all
events they were in harmony, so that the intermissions of discharge were
either isochronous, or a simple ratio existed between the intervals. With a
higher action of the machine, the wires being retained unaltered, the
negative surface became dark and silent, and a glow appeared on the
positive one. A still higher action changed the latter into a spark. Finer
positive wires gave other variations of these effects, the description of
which I must not allow myself to go into here.

1471. A thinner rod was now connected with the negative conductor in place
of the larger one (1468.), its termination being gradually diminished to a
blunt point, as in fig. 124; and it was beautiful to observe that,
notwithstanding the variation of the brush, the same general order of
effects was produced. The end gave a small sonorous negative brush, which
the approach of the hand or a large conducting surface did not alter, until
it was so near as to produce a spark. A fine point opposite to it was
luminous at a distance; being nearer it did not destroy the light and sound
of the negative brush, but only tended to have a brush produced on itself,
which, at a still less distance, passed into a spark joining the two
surfaces.

1472. When the distinct negative and positive