142 0. Barus — Nuclei and Ions in Dust-free Air. 



graphs are of the same kind, nearly parallel, and all of them 

 (energized or not) again terminate in the same asymptote or 

 large green-blue-purple corona. 



The alcohol curves differ from the water curves chiefly in 

 three respects : (1) though the graphs both for the non-energized 

 and energized states terminate in a common asymptote, this 

 is not the green-blue-purple corona, but the white-yellow 

 corona lying slightly below it ; (2) the curves as a whole lie with 

 a somewhat larger slope in a region of much, lower exhaustions 

 (8p)', (3) the number of nuclei caught in alcohol vapor is rela- 

 tively very large. The second and third observations have 

 already been discussed. The first deserves especial considera- 

 tion. The question occurs at once why both the energized 

 and the non-energized curves should be limited by the same final 

 corona, irrespective of the size of the nuclei, and why this 

 should be lower for alcohol than for water. For the ionized 

 state one might infer that the total number of ions has been 

 precipitated, as is actually the case at low ionization ; but if 

 under strong ionization this were true for alcohol vapor, it 

 could not be true for water vapor, where the number of ions 

 caught is less than one-half the number in alcohol. In general 

 it is improbable that the terminal corona for ions should in 

 such a case be the same as the terminal corona for colloidal 

 nuclei. 



The explanation which seems plausible to me is this ; each 

 nucleus must drain the air of its supersaturated moisture 

 within a certain radius large as compared with the size of the 

 nucleus and increasing in the lapse of time. 



A limit of the phenomenon will be reached when for an 

 indefinite number of graded nuclei the enveloping spheres free 

 from supersaturation form a s} 7 stem in contact. In case of 

 water vapor the distance between centers would be '014 cm ; 

 in case of alcohol *010 cm , distances which are both enormous 

 as compared with the estimated size of nuclei (V), Table I. At 

 all events, when the limiting number of nuclei has been cap- 

 tured, the apparatus is powerless to produce condensation on a 

 greater number of nuclei, be they relatively large as the ions 

 or small as the colloidal nuclei, however many other (inefficient) 

 nuclei may be present. 



Brown University, Providence, E. I. 



