Radiation produced hy slowly moving Cathode Rays. 



373 



that of a uniform positive column reaching right up to the 

 negative glow with no Faraday dark space between them. 

 The second case (fig. 6) is when the tangent at P is not 



Kef. 6. 



horizontal : here the curve must cross the tangent at P, 

 becoming concave to .v, and ultimately reaching the axis. 

 Our equations, however, are not true when X is very small, 

 as we have assumed that the field is strong enough to cause 

 the kinetic energy given to the corpuscles by the field to be 

 large compared with the energy they would possess at the 

 same temperature if not acted on by the electric force; we 

 are not therefore at liberty to follow the curve into the region 

 of very small electric forces. 



The effects near the cathode are probably in practice com- 

 plicated by "the action of the c Entladungstrahlen/ discovered 

 by E. Wiedemann, which are given out by the negative 

 glow and, indeed, by all luminous parts of the discharge. I 

 have shown that these rays possess the power of ionizing a 

 gas through which they pass. These rays would therefore 

 increase the ionization in the gas, and would keep the graph 

 for X~* convex to the axis even though the force falls below 

 the value of X : we might thus, under the influence of these 

 rays, get a graph such as that in fig. 7, and this seems 

 to resemble more closely than fig. 6 the distribution of 

 electric force, observed by Graham (Wied. Ann. lxiv. p. 49) 

 in the neighbourhood of the cathode. The intensity of 

 these rays will diminish as we recede from the cathode, and 

 we shall sooner or later reach a place Q, fig. 7 , where the 

 ionization exceeds the recombinations; here the graph hecomes 

 concave to the axis and continues so until X again reaches 

 the value X at R. Here again there are two cases to be con- 

 sidered : (1) when the tangent at R is horizontal ; in this 

 case the rest of the graph is the horizontal straight line 

 through R, and the case is that of a uniform positive column 

 separated by a Faraday dark space from the negative glow. 



