Since then, Richardson and J.J.Thomson have examined analogous phenomena.

This emission is a very general phenomenon which, no doubt, plays a considerable part in cosmic physics.

Professor Arrhenius explains, for instance, the polar auroras by the action of similar corpuscules emitted by the sun.
In other phenomena we seem indeed to be confronted by an emission, not of negative electrons, but of positive ions.

Thus, when a wire is heated, not _in vacuo_, but in a gas, this wire begins to electrify neighbouring bodies positively.

J.J.Thomson has measured the mass of these positive ions and finds it considerable, i.e.about 150 times that of an atom of hydrogen.