278 Mr. W. Sutherland on 



relations of electrons and atoms must be nearly ready for 

 important developments. 



Two more of Lenard's facts are of special importance, 

 namely, that cathode rays, when passed through a window 

 from the vacuum-tube in which they are generated, travel as 

 Lenard rays through gas of such a density as would prevent 

 the formation of the cathode rays, if it prevailed in the tube, 

 whether that density is great, as in the ordinary atmosphere, 

 or very small, as in a vacuum so high as to insulate under the 

 electric forces in the tube. These facts are explained by our 

 theory : the properly exhausted tube furnishes a requisite 

 facility for splitting up the neutrons and getting a supply of 

 electrons to be set swiftly in motion ; once that is accomplished, 

 nothing will stop them until it offers enough resistance to 

 destroy the momentum of the electrons, and ordinary lengths 

 of dense or rare air in Lenard's experiments failed to do this. 

 The action of the tube in generating the cathode rays may be 

 likened in this connexion to a Gifford's Steam Injector. 



In the logical development of the present line of thought, 

 an attempt at an explanation of the cause of the Rontgen 

 rays must find a place. Already J. J. Thomson, in his paper 

 on a Connexion between Cathode and Rontgen Rays (Phil. 

 Mag. [5] xlv., Feb. 1898), has worked out in some detail the 

 electromagnetic effect of suddenly stopping ions moving with 

 high velocity, the main result being that thin electromagnetic 

 pulses radiate from the ion. He believes that these pulses 

 constitute the Rontgen rays, in agreement with a surmise of 

 Stokes. Thomson's reasoning would apply to our free 

 electrons just as to his ions, but there would be this important 

 distinction, that while Thomson's hypothesis involves the 

 condition that the greater part of the energy of the cathode 

 stream consists of the kinetic energy of the atoms, in our 

 hypothesis the energy belongs almost entirely to the moving 

 electrons, and when these are stopped the energy appears as 

 heat at the place of stoppage. Thus Thomson's electromag- 

 netic pulses appear only as subsidiary phenomena in con- 

 nexion with the conversion of the kinetic energy of the 

 electrons into heat ; indeed, we cannot be sure that they 

 exist, because their existence has been suggested only in 

 accordance with the particular assumptions in Thomson's 

 hypothesis which correspond to only a limited portion of the 

 complete electrodynamics of such an action as is contemplated 

 in this paper, causing the conversion of all or almost all the 

 kinetic energy of an electron into heat. Moreover, in tracing 

 the relation of Lenard rays to cathode rays we have been led 

 to picture the stoppage of the moving electrons as nothing 



