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 only a small part of the filament reaches out of this tube.  By holding the tube T_1 anywhere in the electrostatic field the filament is rendered incandescent.

[Illustration:  FIG. 34.—­TUBE WITH FILAMENT RENDERED INCANDESCENT IN AN ELECTROSTATIC FIELD.]

[Illustration:  FIG. 35.—­CROOKES’ EXPERIMENT IN ELECTROSTATIC FIELD.]

A more interesting piece of apparatus is illustrated in Fig. 35.  The construction is the same as before, only instead of the lamp filament a small platinum wire p, sealed in a stem s, and bent above it in a circle, is connected to the copper wire w, which is joined to an inside coating C. A small stem s_1 is provided with a needle, on the point of which is arranged to rotate very freely a very light fan of mica v.  To prevent the fan from falling out, a thin stem of glass g is bent properly and fastened to the aluminium tube.  When the glass tube is held anywhere in the electrostatic field the platinum wire becomes incandescent, and the mica vanes are rotated very fast.

Intense phosphorescence may be excited in a bulb by merely connecting it to a plate within the field, and the plate need not be any larger than an ordinary lamp shade.  The phosphorescence excited with these currents is incomparably more powerful than with ordinary apparatus.  A small phosphorescent bulb, when attached to a wire connected to a coil, emits sufficient light to allow reading ordinary print at a distance of five to six paces.  It was of interest to see how some of the phosphorescent bulbs of Professor Crookes would behave with these currents, and he has had the kindness to lend me a few for the occasion.  The effects produced are magnificent, especially by the sulphide of calcium and sulphide of zinc.  From the disruptive discharge coil they glow intensely merely by holding them in the hand and connecting the body to the terminal of the coil.