1908] on tlie Carriers of Positive Electricity. 195 



should be greater than a certain quantity depending only on the force 

 between the systems and their distance apart when nearest together. 

 M is the mass of the ion, M' that of the molecule, and V the relative 

 velocity of the two at the absidal distance. If M' is very large com- 

 pared with M the condition is that M v- should be greater, while if 

 M' were equal to M, the condition is that ^ M v'^ should be greater 

 than the same quantity ; thus in the second case the ion would take 

 twice as much energy to get free as in the first, and so would be more 

 likely to combine with the molecule. 



Nature of Ionization hy Cathode Rays. 



If, as seems most probable, the positively charged particles are 

 produced from the ionization of the gas by cathode rays, the study 

 of the processes by which this ionization is accomplished may be 

 expected to throw considerable light on the nature of the positive 

 rays. When a gas is ionized by cathode rays, secondary cathode 

 rays are generated, and the author has recently shown * that the 

 maximum velocity of the secondary rays is independent of the 

 velocity of the primary rays. A comparison of the velocity of the 

 secondary rays from gases, as determined in my experiments, with 

 those from metals, measured by Fiichtbauer j shows that there is not 

 much difference between the two. The velocity of the rays from 

 gases was that due to a potential-difference of 40 volts, of those 

 from metals that due to a potential-difference of 33 volts ; the 

 difference between these results is not greater than could be explained 

 by errors of experiment. Thus, as far as our present knowledge 

 goes, the velocity of a secondary cathode ray is independent both of 

 the velocity of the primary ray and varies but little with the nature 

 of the molecule from which the secondary ray is projected. The 

 first result shows that the energy of the secondary ray is not acquired 

 by a corpuscle in the primary rays striking against one in a molecule 

 of a gas and imparting to it sufficient energy to force it out of the 

 molecule, for if this were the case we should expect the energy of 

 the secondary ray to vary quickly with that of the primary. Neither 

 does it seem likely that the energy in the secondary ray is due to a 

 general explosion of the molecule of the gas produced by a gradual 

 accumulation of energy in the molecule from impacts with the primary 

 rays, for then we should expect the energy in the secondary rays to 

 depend largely on the chemical nature of the molecules. 



As a working hypothesis to account for these very striking pro- 

 perties of the secondary rays, I would suggest that perhaps the first 

 stage is ionization by cathode rays, may be the separation from the 

 molecule, not of a single corpuscle, but of an electrically neutral 



* Proc. Camb. Phil. Soc. xiv. p. 540, 1908. 

 t Phys. Zeits. vii. p. 748, 1908. 



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