184 C. Barus — Distribution of Nuclei. 



The difficulty in the present instance, however, seems to be 

 fatal ; for no reason is suggested why the coronas on second or 

 third exhaustion do not eventually show flowerlike distortion, 

 which they never do. In other words, it is here tacitly assumed 

 that only the ions in the " nascent " state, as it were, are appre- 

 ciably diffusible, while the nucleus is relatively a fixture. 

 Again, the effect of secondary radiation is ignored. 



12. Conclusion. — 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 are still in progress. 



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 propor- 

 tionally to the latter, in such a way that each is produced at 

 its own rate depending on incidental conditions. This is best 

 worked out with water nuclei. The subsequent life-history of 

 the nucleation and the ionization is distinct, nuclei being sur- 

 prisingly persistent, ions by "contrast characteristically fleeting. 

 Hence it seems to me to be best in keeping with all the data in 

 hand, to regard the nucleation as the product which owes its 

 growth or origin to the expulsion of the corpuscles represent- 

 ing the concomitant ionization. Ignition and high potential 

 nuclei, X-ray and radiation nuclei in general, phosphorus and 

 water nuclei, produced throughout in strictly dust-free air, all 

 admit of this account of their occurrence and properties. 

 There is no observable case of a process producing ionization 

 without nucleation, although there are many cases of nucleation 

 free from ionization. 



It should be noticed that to produce the condensation on the 

 X-ray air nuclei here in question, less than a twofold super- 

 saturation is needed ; whereas in case of condensation on ions 

 the supersaturation prescribed is three to fourfold. The two 

 views are not, therefore, mutually exclusive. Moreover, if 

 initially, i. e., for short exposures and nuclei in the extreme 

 state of fineness antedating growth, the nucleus is supposed to 

 have ejected but one electron per nucleus (an assumption 

 which in one form or another must be made in any explana- 

 tion), the present view is in no way incompatible with J. J. 

 Thomson's method of measuring the charge of one electron. 

 Finally if a nucleus like that of phosphorus shows a tendency 

 to grow continuously until it finally appears as part of a visi- 

 ble smoke, there may be continuous ejection of electrons 

 within certain limits, as the growth matures. Electric conduc- 

 tion through a gas freighted with these nuclei would obey 

 Ohm's law, as is actually the case for phosphorus. 



Brown University, Providence, E. I. 



