lest bulb.

An interesting observation was made in this experiment. The three
bulbs were suspended from a straight bare wire connected to a terminal
of the coil, the largest bulb being placed at the end of the wire, at
some distance from it the smallest bulb, and an equal distance from
the latter the middle-sized one. The carbons glowed then in both the
larger bulbs about as expected, but the smallest did not get its share
by far. This observation led me to exchange the position of the bulbs,
and I then observed that whichever of the bulbs was in the middle it
was by far less bright than it was in any other position. This
mystifying result was, of course, found to be due to the electrostatic
action between the bulbs. When they were placed at a considerable
distance, or when they were attached to the corners of an equilateral
triangle of copper wire, they glowed about in the order determined by
their surfaces.

As to the shape of the vessel, it is also of some importance,
especially at high degrees of exhaustion. Of all the possible
constructions, it seems that a spherical globe with the refractory
body mounted in its centre is the best to employ. In experience it has
been demonstrated that in such a globe a refractory body of a given
bulk is more easily brought to incandescence than when otherwise
shaped bulbs are used. There is also an advantage in giving to the
incandescent body the shape of a sphere, for self-evident reasons. In
any case the body should be mounted in the centre, where the atoms
rebounding from the glass collide. This object is best attained in
the spherical bulb; but it is also attained in a cylindrical vessel
with one or two straight filaments coinciding with its axis, and
possibly also in parabolical or spherical bulbs with the refractory
body or bodies placed in the focus or foci of the same; though the
latter is not probable, as the electrified atoms should in all cases
rebound normally from the surface they strike, unless the speed were
excessive, in which case they _would_ probably follow the general law
of reflection. No matter what shape the vessel may have, if the
exhaustion be low, a filament mounted in the globe is brought to the
same degree of incandescence in all parts; but if the exhaustion be
high and the bulb be spherical or pear-shaped, as usual, focal points
form and the filament is heated to a higher degree at or near such
points.

To illustrate the effect, I have here two smal