274 Mr. W. Sutherland on 



leads in a most natural manner to a theory of the Lenard rays. 

 The cathode stream of electrons, moving with a velocity 

 nearly that of light, possessing inertia, and yet of a size that 

 is small compared to the molecular interspaces in solids, must 

 be able to penetrate a solid that is thin enough, and to emerge 

 on the other side, differing from the original cathode stream 

 only in that the small trace of moving ions has been filtered 

 out. Practically then Lenard rays are cathode rays. This 

 is what experiment has abundantly proved. All the main 

 properties of the cathode rays have been re-observed in the 

 Lenard rays: thus Perrin proves that the cathode stream 

 carries negative electricity, McClelland proves the same for 

 the Lenard rays : Eontgen discovers that where the cathode 

 stream strikes a solid it emits Rontgen rays ; Des Coudres 

 proves that where the Lenard rays strike a solid they also 

 emit Rontgen rays : Goldstein discovered that the cathode 

 stream colours salts, especially haloid salts of the alkalis, in a 

 remarkable way; Des Coudres proves the same for the 

 Lenard stream: and so on with such properties as magnetic and 

 electric deflectability, power of exciting luminescence, and 

 the like. The cathode and Lenard streams are the simplest 

 forms of electric current known to us. Such a power as that 

 of causing certain substances to emit light is only another form 

 of our fundamental principle, that an electron in having its 

 motion arrested imparts energy to the arresting molecules, 

 and of course to their associated electrons. The colouring of 

 salts discovered by Goldstein would be accounted for by the 

 supposition that some of the negative electrons attach them- 

 selves to the electronegative atoms, thereby converting them 

 into free ions, and liberating uncharged atoms of the metal, 

 which cause the coloration. The experiments which have 

 been made, with negative results, to detect the metal or the 

 ion chemically do not decide anything, because of course the 

 amounts produced are too small for ordinary methods of 

 analysis to detect. The fatigue, which some substances show 

 after fluorescing for a while under the influence of the cathode 

 stream, may be' accounted for in a similar manner by the 

 lodgement of free electrons, which produce an opposing 

 electromotive force and diminish the intensity of the cathode 

 stream, while at the same time producing an analogous change 

 to the change of colour in the salts studied by Goldstein, 

 except that the change does not appear as visible colour, but 

 as a lowering of fluorescent power. Fluorescence is known 

 to be very sensitive to the presence of small traces of sub- 

 stances. 



We do not know enough of the relations of atoms and 



