Electric Discharges in Rarefied Gases. 71 



stating that the negative rays mark the path of a sheaf of 

 charged particles, and therefore in general it is a spiral in a 

 uniform field. A sheaf of rays normal to a pole of a magnet 

 forms loops and nodes, as shown by Poincare. 



Crookes' theory regards the cathode rays as streams of nega- 

 tively electrified particles driven with great speed away from 

 the cathode. The heating effects are explained by supposing 

 that the kinetic energy of the particles is partly transformed by 

 impact. 



A rapidly moving particle acts like an electric current, and 

 produces round it a magnetic field ; when the particle is stopped 

 the field is destroyed. This rapid change in the field produces 

 rapidly changing electro-magnetic forces, analogous on the 

 electro-magnetic theory to the conditions which accompany 

 ultra-violet light, and therefore phosphoresence. 



The phenomena of the discharge have led us to believe that 

 the molecules are broken up, and that chemical actions essen- 

 tially accompany the passage of electricity through gas. 



We can readily admit that the molecules of gases, which con- 

 sist of two atoms, can be broken up by the current ; but there 

 is a difficulty in the case of mercury vapour, which must be 

 regarded as mon -atomic. 



If, then, the dissociation theory is correct, we must, as War- 

 burg pointed out, suppose that the mon-atomic mercury vapour 

 may also be further analysed, and, by electric discharges, 

 carriers of electricity are produced, which are small in com- 

 parison with the ordinary atom or molecule. 



