inly
those which are noted in an electrostatic field acting through
considerable distance, and the best an unskilled lecturer can do is
to begin and finish with the exhibition of these singular effects. I
take a tube in the hand and move it about, and it is lighted wherever
I may hold it; throughout space the invisible forces act. But I may
take another tube and it might not light, the vacuum being very high.
I excite it by means of a disruptive discharge coil, and now it will
light in the electrostatic field. I may put it away for a few weeks or
months, still it retains the faculty of being excited. What change
have I produced in the tube in the act of exciting it? If a motion
imparted to the atoms, it is difficult to perceive how it can persist
so long without being arrested by frictional losses; and if a strain
exerted in the dielectric, such as a simple electrification would
produce, it is easy to see how it may persist indefinitely, but very
difficult to understand why such a condition should aid the excitation
when we have to deal with potentials which are rapidly alternating.

Since I have exhibited these phenomena for the first time, I have
obtained some other interesting effects. For instance, I have produced
the incandescence of a button, filament, or wire enclosed in a tube.
To get to this result it was necessary to economize the energy which
is obtained from the field and direct most of it on the small body to
be rendered incandescent. At the beginning the task appeared
difficult, but the experiences gathered permitted me to reach the
result easily. In Fig. 34 and Fig. 35 two such tubes are illustrated
which are prepared for the occasion. In Fig. 34 a short tube T_1,
sealed to another long tube T, is provided with a stem s, with a
platinum wire sealed in the latter. A very thin lamp filament l is
fastened to this wire, and connection to the outside is made through a
thin copper wire w. The tube is provided with outside and inside
coatings, C and C_1 respectively, and is filled as far as the coatings
reach with conducting, and the space above with insulating powder.
These coatings are merely used to enable me to perform two experiments
with the tube--namely, to produce the effect desired either by direct
connection of the body of the experimenter or of another body to the
wire w, or by acting inductively through the glass. The stem s is
provided with an aluminium tube a, for purposes before explained, and
on