CHAPTER IX.
CATHODE RAYS AND RADIOACTIVE BODIES Sec.1.THE CATHODE RAYS A wire traversed by an electric current is, as has just been explained, the seat of a movement of electrons.

If we cut this wire, a flood of electrons, like a current of water which, at the point where a pipe bursts, flows out in abundance, will appear to spring out between the two ends of the break.
If the energy of the electrons is sufficient, these electrons will in fact rush forth and be propagated in the air or in the insulating medium interposed; but the phenomena of the discharge will in general be very complex.

We shall here only examine a particularly simple case, viz., that of the cathode rays; and without entering into details, we shall only note the results relating to these rays which furnish valuable arguments in favour of the electronic hypothesis and supply solid materials for the construction of new theories of electricity and matter.
For a long time it was noticed that the phenomena in a Geissler tube changed their aspect considerably, when the gas pressure became very weak, without, however, a complete vacuum being formed.

From the cathode there is shot forth normally and in a straight line a flood within the tube, dark but capable of impressing a photographic plate, of developing the fluorescence of various substances (particularly the glass walls of the tube), and of producing calorific and mechanical effects.

These are the cathode rays, so named in 1883 by E.Wiedemann, and their name, which was unknown to a great number of physicists till barely twelve years ago, has become popular at the present day.
About 1869, Hittorf made an already very complete study of them and put in evidence their principal properties; but it was the researches of Sir W.Crookes in especial which drew attention to them.