to perform the experiment in a more suitable manner, the button was taken so large that a perceptible time had to elapse before, upon grasping the bulb, it could be rendered incandescent.  The contact with the bulb was, of course, quite unnecessary.  It is easy, by using a rather large bulb with an exceedingly small electrode, to adjust the conditions so that the latter is brought to bright incandescence by the mere approach of the experimenter within a few feet of the bulb, and that the incandescence subsides upon his receding.

[Illustration:  FIG. 24.—­BULB WITHOUT LEADING-IN WIRE, SHOWING EFFECT OF PROJECTED MATTER.]

In another experiment, when phosphorescence was excited, a similar bulb was used.  Here again, originally, the potential was not sufficient to excite phosphorescence until the action was intensified—­in this case, however, to present a different feature, by touching the socket with a metallic object held in the hand.  The electrode in the bulb was a carbon button so large that it could not be brought to incandescence, and thereby spoil the effect produced by phosphorescence.

[Illustration:  FIG. 25.—­IMPROVED EXPERIMENTAL BULB.]

Again, in another of the early experiments, a bulb was used as illustrated in Fig. 12.  In this instance, by touching the bulb with one or two fingers, one or two shadows of the stem inside were projected against the glass, the touch of the finger producing the same result as the application of an external negative electrode under ordinary circumstances.

In all these experiments the action was intensified by augmenting the capacity at the end of the lead connected to the terminal.  As a rule, it is not necessary to resort to such means, and would be quite unnecessary with still higher frequencies; but when it is desired, the bulb, or tube, can be easily adapted to the purpose.

[Illustration:  FIG. 26.—­IMPROVED BULB WITH INTENSIFYING REFLECTOR.]

In Fig. 24, for example, an experimental bulb L is shown, which is provided with a neck n on the top for the application of an external tinfoil coating, which may be connected to a body of larger surface.  Such a lamp as illustrated in Fig. 25 may also be lighted by connecting the tinfoil coating on the neck n to the terminal, and the leading-in wire w to an insulated plate.  If the bulb stands in a socket upright, as shown in the cut, a shade of conducting material may be slipped in the neck n, and the action thus magnified.

A more perfected arrangement used in some of these bulbs is illustrated in Fig. 26.  In this case the construction of the bulb is as shown and described before, when reference was made to Fig. 19.  A zinc sheet Z, with a tubular extension T, is slipped over the metallic socket S. The bulb hangs downward from the terminal t, the zinc sheet Z, performing the double office of intensifier and reflector.  The reflector is separated from the terminal t by an extension of the insulating plug P.