HIGH FREQ UENCY AND HIGH POTENTIAL CURRENTS. 401

—this bombardment being evident from the rapid heating of theglass near the primary. Were the bombardment not at rightangles to the glass the heating could not be so rapid. If thereis a circumferential movement of the molecules constituting theluminous circle, I have thought that it might be rendered mani-fest by placing within the tube or bulb, radially to the circle, athin plate of mica coated with some phosphorescent material andanother such plate tangentially to the circle. If the moleculeswould move circumferentially, the former plate would be ren-dered more intensely phosphorescent. For want of time I have,however, not been able to perform the experiment.

Another observation made by me was that when the specificinductive capacity of the medium between the primary andsecondary is increased, the inductive effect is augmented. Thisis roughly illustrated in Fig. 215. In this case luminosity wasexcited in an exhausted tube or bulb b and a glass tube t slippedbetween the primary and the bulb, when the effect pointed outwas noted. Were the action wholly electromagnetic no changecould possibly have been observed.

I have likewise noted that when a bulb is surrounded by awire closed upon itself and in the plane of the primary, the for-mation of the luminous circle within the bulb is not prevented.But if instead of the wire a broad strip of tinfoil is glued uponthe bulb, the formation of the luminous band was prevented, be-cause then the action was distributed over a greater surface. Theeffect of the closed tinfoil was no doubt of an electrostatic nature,for it presented a much greater resistance than the closed wireand produced therefore a much smaller electromagnetic effect.

Some of the experiments of Prof. J. J. Thomson also wouldseem to show some electrostatic action. For instance, in the ex-periment with the bulb enclosed in a bell jar, I should thinkthat when the latter is exhausted so far that the gas enclosedreaches the maximum conductivity, the formation of the circlein the bulb and jar is prevented because of the space surroundingthe primary being highly conducting; when the jar is furtherexhausted, the conductivity of the space around the primarydiminishes and the circles appear necessarily first in the bell jar,as the rarefied gas is nearer to the primary. But were the in-ductive effect very powerful, they would probably appear in thebulb also. If, however, the bell jar were exhausted to the high-est degree they would very likely show themselves in the bulb