74 BARUS— NUCLEI IN DUST-FREE WET AIR. f April 20, 



increasing with hp/p. Numerically {vjv) — i is not very different 

 from hp/p. 



The charts contain an exhibit both of the older results and of 

 new results. In the former the effect of rise of temperature in 

 increasing the available nucleation to the extent of 5-10 per cent. 

 per degree C, is marked. The earlier results are given in Figures 

 2 and 3. 



In the new series (Figs. 4 and 5) and in case of vapor nuclei, 

 the efficiency of the fog chamber breaks down above the green 

 corona at about 1.5 X lo*^ nuclei per cubic centimeter; Bp/p == .41; 

 £'1/1'= 1.45. Below this, the graph showing distribution and size 

 of nuclei is well given, ascending definitely from about 8p/p = .2>i, 

 vjv=^ 1.30, which may be called the fog limit. Finally the region 

 of ions appears as a well marked feature of the curve, extending 

 from about 8/'//' = .31 to hp/p =-■ .262, z'-i/z' = 1.24, where condensa- 

 tion begins (negative ions) for vapor nuclei. This is definitely be- 

 low Wilson's point 7'yT'=i.25, for negative ions. 



Exposed to the beta and gamma rays of Radium (io,oooX, 

 300 mg.), the limiting ionization observed is below 200,000 nuclei 

 per cubic centimeter; exposed to radium (10,000 X , 700 mg.), it is 

 below 300,000 nuclei per cubic centimeter; but the condensation 

 begins at Bp/p ^ .26, or somewhat below ^'1/7'= 1.23, distinctly 

 below the case for dust-free wet air. 



The X-rays finally lower this condensation limit still further to 

 8/>//> ^ .247, or somewhat below ?:'i/'t^= 1.223, definitely below the 

 point for the weak radium radiation. As compared with the 

 curve for vapor nuclei the steepness of the X-ray curve with strong 

 radiation, its almost sudden ascent is a further feature. It does 

 not however, in my apparatus, get above the large green corona; 

 i. e., about lo*^ nuclei per cubic centimeter are caught at 8/>//' = .29, 

 or vjv^ 1.27. 



One may notice, therefore, that the plug cock fog chamber puts 

 both condensation points as well as the corresponding distribution 

 of vapor nuclei, definitely hcloiv the values obtained by Wilson in 

 his piston apparatus (marked W in the charts 2 and 3, 4 and 5). 

 Moreover the march of the limits of condensation due to a given 



