CATHODE RAYS AND RONTGEN RAYS. 281 



projectiles negatively electrified. Why should they move in a straight 

 line perpendicularly to the surface of the cathode? Because they are 

 repulsed and driven violently by the electric charge of the cathode. 



The electro-metric and electro-magnetic measurements, combined 

 with those of which we have formerly spoken, and which allow the 

 calculation of the number of cathode projectiles in a given space by 

 means of the condensation of a mist have led to surprising results 

 whose accuracy is amazing. By these means the cathode projectile 

 has been found to have a constant mass, equal to the thousandth part 

 of one atom of hydrogen. 



The projectile, then, does not depend upon the cathode, as Crookes 

 had already determined. It is composed of hydrogen, as proved by 

 M. Villard without question. It has its origin necessarily in the 

 breaking up of the atom of hydrogen. This, instead of being the 

 final expression of simplicity and of lightness, as chemists believe, 

 appears to be a quite complex edifice and rather heavy, since the cur- 

 rent of the Crookes tube removes from the stones which represent it 

 but the thousandth part of its mass. These stones are the fragments 

 of atoms, or the atomic corpuscles of J. J. Thomson. The atom is no 

 longer indivisible. Here we shall stop, not pushing the analysis fur- 

 ther, although the state of science would permit it; but we should 

 enter upon the subject of the constitution of matter, a subject which 

 can only be incidentally referred to here. 



III. 



Cathode rays have no practical application. They are produced 

 under extremely peculiar conditions, in a barometric vacuum, in the 

 interior of a bulb from which it is almost impossible to liberate them. 

 We should have no excuse for having entertained our readers so long 

 had this stud} T offered only the interest of pure curiosity and an 

 opportunity of proclaiming the cleverness of our physicists. But it 

 has another bearing. In narrating the history of these rays we hav 

 included that of rays of the same family — Rontgen rays, of which th 

 applications are so numerous, and Becquerel rays, which are but a 

 mixture of the two other kinds. In the second place, the cathode rays 

 are the progenitors and the necessar} 7 generators of the others. The 

 mechanism and the true nature of the latter are better known. 



Moreover, cathode rays (and Rontgen rays as well as those of 

 Becquerel, which accompany them or emanate from them) are not 

 merely the simple results of design on the part of physicists; they con- 

 stitute a natural phenomenon which can not be neglected. Far from 

 being of rare occurrence they are incessantl}' produced. Not a single 

 ray from the sun falls upon a metallic surface, not a flame is ignited, 

 not an electric spark Hashes, not a current of electricity is produced, 

 not a substance becomes incandescent without the appearance of a 



