Cathode^ Lenard, and Rbntgen Rays. 217 



depends on its molecular radius, but the data hardly permit 

 of an examination into this point. It should be remarked 

 that, as the electron can probably pass easily between the 

 atoms in a molecule, the absorption due to a compound mole- 

 cule ought to be analysed into the parts due to its atoms ; 

 for instance, in Lenard's table of values for A in such gases 

 as CH 4 , C0 2 , C 2 H 4 , the part due to the carbon, the hydrogen, 

 and the oxygen, ought to be separated out, and then each 

 part ought to be proportional to the atomic mass and inversely 

 proportional to the atomic radius. If this is so, then the 

 agreement in the values of RA/m in our table could not be 

 expected to be perfect. 



A very characteristic property of the Lennrd rays follows 

 from our theory, for when the cathode rays fall on an alu- 

 minium window, such as Lenard used, they have a direction 

 normal to it, whereas the Lenard rays issuing on the other 

 side of the window are uniformly radiated in all directions ; 

 and this is exactly how our stream of small electrons would 

 behave, because after they have threaded their way through 

 the molecular interstices, they will issue with directions 

 uniformly distributed in space, for it is to be presumed that 

 the final directions of the intermolecular passages will be 

 distributed at random. 



As the cathode and Lenard streams are currents of electrons, 

 and therefore form pure electric currents, we might expect 

 a priori that the coefficient of absorption of substances for 

 them would show some decided relation to the electrical 

 resistance of the substances ; but Lenard's law proves that 

 such an expectation would be futile, for the absorption of 

 conductor and insulator alike depends almost entirely on 

 density. This fact throws considerable light on the nature 

 of metallic conduction. It would seem as if in the conduction 

 of electricity in metals, both the positive and negative elec- 

 trons, distributed through the metals, take part in the process 

 of conduction, probably in the method of the Grothuss chain; 

 by a process of exchange of partners both kinds of electron 

 get passed along in opposite directions without anything of 

 the nature of a great rush of one kind of electron at one time 

 and place. When such a rush occurs in a cathode stream, 

 the internal appliances of the best conducting metal can no 

 more facilitate its passage, than can the obstructing appliances 

 of the best insulator hinder it. In metallic conduction we 

 have to do with a property of the metallic atom, whereby, 

 with the aid of electromotive force, the local dissociation of 

 the neutron into electrons is greatly facilitated ; whereas in 

 insulators the reverse is the case. This important field of the 



