10 NUCLEATION OF THE UNCONTAMINATED ATMOSPHERE. 



on second exhaustion even after the first coronas have quite dropped 

 out, etc., are all in a measure accounted for. 



Finally, one may note that secondary radiation (the importance of 

 which I at first underestimated) issuing from the top and the bottom 

 of the condensation chamber would accentuate the present effect, or 

 even wholly replace it. 



Thus it seems not unreasonable to infer that nuclei are produced by 

 the impinging X-rays in much the same way in which they are pro- 

 duced by high temperature (ignition), or by high potential; and the 

 question arises whether the nuclei thus put in evidence may not be 

 associated with the electrons to which the cohesions between the 

 molecules may be ascribed. 



11. Absorption of ions at walls of receiver. if the nuclei due to the 

 ionization of air by the X-rays are absorbed at the walls of the receiver * 

 a diffusion gradient will be established, resulting in a decreasing num- 

 ber of nuclei from the axis outward, a distribution the reverse of the 

 preceding. The observed distortion will therefore here be due to a 

 gradation in the numbers of nuclei. 



One difficulty in the present instance seems at first sight to be fatal; 

 for no reason is suggested why the coronas on second and third 

 exhaustion do not eventually show flower-like distortion, which they 

 never do. In other words, it is here tacitly assumed that only the 

 nuclei in the nascent state, as it were, are appreciably:diffusible, while 

 the nucleus is relatively a fixture. It will be shown in Chapter III, 

 however, that on second and third exhaustion all the nuclei have 

 probably been converted into solutional water nuclei by evaporation, 

 so that the difficulty in question is not serious. 



12. Summary. To decide between these hypotheses it is necessary 

 to guide the X-rays by screens, suitably placed both on the inside and 

 the outside of the apparatus; but these experiments will, in the suc- 

 ceeding chapters, lead to results much too diffuse and complicated in 

 character to be summarized at present. 



Here there is room only for a final remark. Whenever nucleation 

 and ionization are associated as the outcome of any process (physical 

 or chemical), the former is generated proportionally to the latter, in 

 such a way that each is produced at its own rate depending on iiici- 



*A number of similar cases have been worked out in Smithsonian Contributions, 

 No. 1309, 1901, "Experiments with ionized air;" and ibid., No. 1373, Chapter V, 1903. 



