300 Barus — Groups of Efficient Nuclei in Dust-Free Air. 



tation are at once restored. Again air left without interference 

 for days shows a maximum of this nucleation for the given 

 conditions of exhaustion when all foreign nucleation must have 

 vanished. Indeed the molecules themselves may be treated as 

 a continuous part of the nucleation in question, the frequency 

 of occurrence being a maximum for the molecular dimensions. 



Furthermore in the presence of radium the character of the 

 phenomenon is the same, only the nuclei are larger. If with- 

 drawn by precipitation, they are at once restored. They are 

 an essential part of the air in the new environment. 



It is natural to compare the particular nuclear status intro- 

 duced in the latter case by a particular kind of radiation (7 

 rays), with the former case of dust-free air in the absence of 

 recognized radiation. In other words, quite apart from the 

 details of the mechanism, chemical agglomeration might be 

 considered referable to an unknown radiant field, but be other- 

 wise essentially alike in kind to the much coarser nucleations 

 observed in the known radiant fields of the above experiments. 

 But the effect of radium, however distant, is always virtually 

 an increase of the size of the air nuclei and a decrease of their 

 number. Hence if we were to fancy that the nucleation (not 

 the ions, of course) of non-energized dust-free air responds to 

 its own radiant environment, this radiation would have to be 

 special in kind. 



Returning to the case of the gamma rays, fig. % (or of the 

 X-rays coming from a distance,) let me recall that the effective 

 radiation within the fog chamber is everywhere the same and 

 the same in all directions. Hence whether the radiation be 

 corpuscular or (in other cases) undulatory, the interior is noth- 

 ing less than an ideal Lesage medium ; and there must there- 

 fore be a tendency at least to agglomerate the colloidal nuclei 

 of dust-free air into fleeting nuclei or ions, so long as the 

 radiation lasts. When it ceases the ions are free to fall apart, 

 so far as external influence goes, as they actually do. Further- 

 more since the pressure so obtained would increase with the 

 number of corpuscles per cubic cm. and with the square of 

 their velocity, it is conceivable that with increasing electrifica- 

 tion this pressure would become strong enough to bring about 

 permanent union of the aggregates, corresponding to the 

 observed continuous transition of the ions into persistent 

 nuclei, produced by the X-rays. Again a different nucleus 

 would presumably correspond to the bombardment of the 

 negative corpuscles as compared with the residual positive 

 quantities. Finally, if any physical or chemical process like 

 combustion or ignition or electric charge, or the case of phos- 

 phorus, etc. is accompanied by intense ionization, one would 

 for the same reason anticipate the presence of nuclei in such a 

 field. 



Brown University, Providence. 



