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XX. Cathode, Lenard, and Rontgen Rays. 

 By William Sutherland *. 



^PO explain the results of his experiments on cathode rays, 

 *- and to account for the Hertz-Lenard apparent passage 

 of cathode rays through solid bodies according to Lenard's 

 wonderfully simple law, J. J. Thomson (Phil. Mag. [5] . 

 xliv., Oct. 1897) proposes the hypothesis, that the matter in 

 the cathode stream consists of atoms resolved into particles 

 of that primitive substance out of which atoms have been 

 supposed to be composed. Before a theory of such 

 momentous importance should be entertained, it is necessary 

 to examine whether the facts to be explained by it are not 

 better accounted for by the logical development of established 

 or widely accepted principles of electrical science. 



The chief facts which Thomson arrives at from his experi- 

 ments are : — That the cathode rays travel at the same speed 

 in different gases such as hydrogen, air, and carbonic dioxide; 

 and that m/e, the ratio of the mass of the particles to their 

 charge, is the same for the cathode streams in all gases, and 

 is about 10 -3 of the ratio of the mass of the hydrogen atom 

 to its charge in ordinary electrolysis. These seeming facts 

 have also been brought out with great distinctness in the 

 experiments of Kaufmann (Wied. Ann. lxi. and lxii.). 

 Whatever proves to be the right theory of the nature of the 

 cathode rays, the quantitative results which these experi- 

 menters have obtained (as did also Lenard), in a region, 

 where, amid a bewildering wealth of qualitative work, the 

 quantitative appeared as if unattainable, must constitute a 

 firm stretch of the roadway to the truth. 



Let us briefly consider the theories used by J. J. Thomson 

 and by Kaufmann to interpret their experiments. For instance, 

 Thomson considers N particles projected from the cathode, 

 each of mass ra, to strike a thermopile, to which they give up 

 their kinetic energy |Nmv 2 measured as W. Each of the 

 particles carries its charge of electricity e, the whole quantity 

 Ne being measured as Q. Thus we have 



±v 2 m/e = W/Q (1) 



But again, the particles, after being projected through a slit 

 in the anode with velocity v, are subjected to a field H of 

 magnetic force at right angles to the direction of motion, so 

 that the actual force tending to deflect each particle is Hev 

 at right angles to H and v. The result is that each particle 

 describes a circular path of radius p with the centrifugal 



* Communicated by the Author. 

 Phil. Mag. S. 5. Vol. 47. No. 286. March 1899. U 



