C. Barus — Ions and Nuclei in Dust-free Air. 451 



snpersatnrations and the asymptotes (or maxima) are in every 

 case reached and much higher in value. The range of super- 

 saturation within which the condensations begin and are nearly 

 completed is reduced so that the curves are usually steeper. 

 In case of the new curve for non-energized air (and to the 

 same extent in the others) the relative absence of nuclei in the 

 region of ions is a distinguishing peculiarity. Investigated by 

 the coronal methods, the curves rise, as it were, abruptly from 

 the abscissa, and there is a rise of fog limit. 



Fig. 1. — Charts for Table III, showing the coronal apertures (angular 

 diameter being s/30) in cases of different sirpersatnration (pressure drop on 

 exhaustion dp) in cases of non-energized dust-free air, and of dust-free air 

 energized by radium and the X-rays from different distances, D. The dotted 

 curve corresponds to less rapid exhaustion (Table I). Its intersection with 

 the corresponding curve drawn in full should be noticed. It indicates the 

 presence of a group of larger nuclei present in the former case and absent in 

 the latter. 



5. In connection with the present data, different suggestions 

 made in the earlier paper and diverging from the more usual 

 explanations, may be recalled : The effect of radiation if not 

 too strong, has been shown to be virtually an aggregation 

 of the colloidal nuclei of dust-free air. It seems probable 



