HIGH FREQUENCY AND HIGH POTENTIAL CURRENTS. 327

cent. It also showed another interesting feature, bearing uponthe preceding remarks, namely, when the filament had beenkept incandescent some time, the narrow tube and the space in-side were brought to an elevated temperature, and as the gas inthe tube then became conducting, the electrostatic attraction be-tween the glass and the filament became very weak or ceased, andthe filament came to rest. When it came to rest it would glowfar more intensely. This was probably due to its assuming theposition in the centre of the tube where the molecular bombard-ment was most intense, and also partly to the fact that the indi-vidual impacts were more violent and that no part of the suppliedenergy was converted into mechanical movement. Since, in ac-cordance with accepted views,in this experiment the incandescencemust be attributed to the impacts of the particles, molecules oratoms in the heated space, these particles must therefore, in orderto explain such action, be assumed to behave as independent car-riers of electric charges immersed in an insulating medium ; yetthere is no attractive force between the glass tube and the fila-ment because the space in the tube is, as a whole, conducting.

It is of some interest to observe in this connection that whereasthe attraction between two electrified bodies may cease owing tothe impairing of the insulating power of the medium in whichthey are immersed, the repulsion between the bodies may still beobserved. This may be explained in a plausible way. When thebodies are placed at some distance in a poorly conducting medium,such as slightly warmed or rarefied air, and are suddenly electri-fied, opposite electric charges being imparted to them, thesecharges equalize more or less by leakage through the air. But ifthe bodies are similarly electrified, there is less opportunity af-forded for such dissipation, hence the repulsion observed in suchcase is greater than the attraction. Ilepulsive actions in a gas-eous medium are however, as Prof. Crookes has shown, enhancedby molecular bombardment.

ON CURRENT OR "DYNAMIC ELECTRICITY PHENOMENA.

So far, I have considered principally effects produced by avarying electrostatic force in an insulating medium, such as air.When such a force is acting upon a conducting body of measur-able dimensions, it causes within the same, or on its surface,displacements of the electricity and gives rise to electric currents,and these produce another kind of phenomena, some of which 1