C. Bancs — Ions and Nuclei in Dust-free Air. 453 



time the existing nuclei are further aggregated into larger 

 systems. 



Within the fog-chamber it is probable that the radiations 

 whether undulatory or corpuscular, is at any point the same in 

 all directions, for the nuclei in any given case are largely 

 produced by secondary radiation. 



Hence it follows, qualitatively at least, that the inside of the 

 fog-chamber is an ideal Lesage medium. One may argue, 

 therefore, that a corresponding tendency for the preexisting 

 colloidal nuclei of dust-free air to aggregate into ions or larger 

 bodies, should be manifest. Again the ions, conditioned by 

 the presence of radiation, must fall apart when the radiation is 

 withdrawn, and this is the case. One may infer also that the 

 nucleating effect produced by negative corpuscles would be 

 different from that corresponding to the positive residuals. 



Let the kinetic ionization pressure be supposed to increase 

 as the square of the velocity of the corpuscles and as their 

 density of distribution; then if the ionization becomes very 

 intense it is possible that the pressure becomes strong enough 

 to produce permanent union of the loose aggregates, or that 

 the fleeting nuclei eventually become persistent, as is the case. 



If the ionized field is intensely produced by corpuscles issu- 

 ing from within the body itself, as for instance, in combustion, 

 or ignition, etc., one may expect that large nuclei as well as 

 fleeting nuclei should simultaneously appear ; or that nuclea- 

 tion, passing through a transitional stage from fleeting to per- 

 sistent as the electrification is more intense, should be the 

 invariable concomitant of ionization. It is probable that the 

 expulsion of corpuscles takes place whenever persistent nuclei 

 are produced. Thus in the case of the X-rays, the generation 

 of persistent nuclei occurs at an accelerated rate with time for 

 a fixed radiation. If the radiation is cut off, nuclei are spon- 

 taneously generated (secondary generation) for some time after. 



Arguments to the same effect would follow for light pres- 

 sure for wave lengths small enough to be easily scattered. 

 Thus persistent and fleeting nuclei as a simple continu- 

 ous phenomenon are produced by the X-rays (Table II), in 

 the manner identical with the case of ultra-violet light. Simi- 

 larly nuclei grow large in size as the ignition, the potential 

 differences, etc., are larger. 



Finally, although the colloidal nucleation of dust-free air 

 may be conceived to be aggregated both by nndulatory and by 

 corpuscular pressure, it is only in the latter case that the 

 nuclei can be influenced by an electric field because the cor- 

 puscles are themselves actuated. This distinction in fact exists 

 between nuclei otherwise quite identical fleeting or persistent, 

 but produced in one case by ultra-violet light and in the other 

 by the X-rays or the action of radium. 



Brown University, Providence, R. I. 



