point downwards in free air; let it be amalgamated, and have a
drop of mercury suspended from it; and then let it be powerfully
electrized. The mercury will present the phenomenon of _glow_; a current of
air will rush along the rod, and set off from the mercury directly
downwards; and the form of the metallic drop will be slightly affected, the
convexity at a small part near the middle and lower part becoming greater,
whilst it diminishes all round at places a little removed from this spot.
The change is from the form of _a_ (fig. 135.) to that of _b_, and is due
almost, if not entirely, to the mechanical force of the current of air
sweeping over its surface.

1582. As a comparative observation, let it be noticed, that a ball
gradually brought towards it converts the glow into brushes, and ultimately
sparks pass from the most projecting part of the mercury. A point does the
same, but at much smaller distances.

1583. Take next a drop of strong solution of muriate of lime; being
electrified, a part will probably be dissipated, but a considerable
portion, if the electricity be not too powerful, will remain, forming a
conical drop (fig. 136.), accompanied by a strong current. If glow be
produced, the drop will be smooth on the surface. If a short low brush is
formed, a minute tremulous motion of the liquid will be visible; but both
effects coincide with the principal one to be observed, namely, the regular
and successive charge of air, the formation of a wind or current, and the
form given by that current to the fluid drop, if a discharge ball be
gradually brought toward the cone, sparks will at last pass, and these will
be from the apex of the cone to the approached ball, indicating a
considerable degree of conducting power in this fluid.

1584. With a drop of water, the effects were of the same kind, and were
best obtained when a portion of gum water or of syrup hung from a ball
(fig. 137.). When the machine was worked slowly, a fine large quiet conical
drop, with concave lateral outline, and a small rounded end, was produced,
on which the glow appeared, whilst a steady wind issued, in a direction
from the point of the cone, of sufficient force to depress the surface of
uninsulated water held opposite to the termination. When the machine was
worked more rapidly some of the water was driven off; the smaller pointed
portion left was roughish on the surface, and the sound of successive brush
discharges was heard. With sti