st dividing the tube into two
compartments. This pocket, silvered on the air side, forms a hollow
glass diaphragm that can be connected electrically from the outside,
forming the negative pole, A; the two ends of the tube, also outwardly
silvered, form the positive poles, B B. I pass the current, and you
will see the dark space distinctly visible. The pressure here is 0.076
millimeter, or 100 M. The next stage, dealing with more rarefied
matter, is that of phosphorescence. Here is an egg-shaped bulb, shown
in Fig 19, containing some pure yttria and a few rough rubies. The
positive electrode, B, is on the bottom of the tube under the
phosphorescent material; the negative, A, is on the upper part of the
tube. See how well the rubies and yttria phosphorescence shows under
molecular bombardment, at an internal pressure of 0.00068 millimeter,
or 0.9 M.

[Illustration: FIG. 18.--PRESSURE = 0.076 MM. = 100 M.]

A shadow of an object inside a bulb can also be projected on to the
opposite wall of the bulb by means of an outside pole. A mica cross is
supported in the middle of the bulb (Fig. 20), and on connecting a
small silvered patch, A, on one side of the bulb with the negative
pole of the induction coil, and putting the positive pole to another
patch of silver, B, at the top, the opposite side of the bulb glows
with a phosphorescent light, on which the black shadow of the cross
seems sharply cut out. Here the internal pressure is 0.00068
millimeter, or 0.9 M.

[Illustration: FIG. 19.--PRESSURE = 0.00068 MM. = 0.9 M.]

[Illustration: FIG. 20.--PRESSURE = 0.00068 MM. = 0.9 M.]

[Illustration: FIG. 21.--PRESSURE = 0.001 MM. = 1.3 M.]

Passing to the next phenomenon, I proceed to show the production of
mechanical energy in a tube without internal poles. It is shown in
Fig. 21 (P = 0.001 millimeter, or 1.3 M). It contains a light wheel of
aluminum, carrying vanes of transparent mica, the poles, A B, being in
such a position outside that the molecular focus falls upon the vanes
on one side only. The bulb is placed in the lantern and the image is
projected on the screen; if I now pass the current, you see the wheels
rotate rapidly, reversing in direction as I reverse the current.

Here is an apparatus (Fig. 22) which shows that the residual gaseous
molecules when brought to a focus produce heat. It consists of a glass
tube with a bulb blown at one end and a small bundle of carbon wool,
C, fixed in the center, and exhausted