>(?. Barns — Rate of Decay of Nuclei. 



107 



Art. XV. — The Rate of Decay of Different Sizes of Nuclei, 

 Determined by Aid of the Coronas of Cloudy Condensa- 

 tion '* by C. Barus. 



A series of experiments into which I entered at some length 

 and which, though from the nature of the experiment they 

 cannot lay claim to a high order of precision, nevertheless lead 

 to very definite results, are contained in the following table, 

 which is an example of many similar results. These nuclei 

 were produced by X-rays (of moderate intensity) in an alumi- 

 num-covered fog chamber, with short exposures to the radia- 

 tion. The data show that no persistent nuclei of the usual 

 large type appreciably occur, since these, if present, require 

 almost no supersaturation of moist air, for condensation. 

 Moreover, the vapor nuclei of dust-free wet air are not caught 

 in my fog chamber, in the presence of ions, or else their num- 

 ber is specially determined and small in comparison with the 

 nuclei here obtained by the X-rays. This premised, the table 

 gives the relative drop of pressure hp/jp from p, the lapse of 



Table.— Decay of different sizes of nuclei (radius r), the number n present 

 being determined by the coronas of cloudy condensation, dn/dt = — bn*. 





t 









6 p / p 



Lapse, sec. 



n x 10 -3 



fcxlO 6 



rxlO 1 



•26 







73-8 



43 



•66 





30 



•9 





__ 



-- 



15 



1-3 



-- 



-- 



•28 







484* 



2 



•61 



-- 



30 



15-7 



-- 



-- 



•30 



15 



32-8 



3 



•54 



-- 



60 



6*4 



-- 



-- 



•33 



15 



36-8 



•4 



•48 



.. 



60 



29-7 









30 



29-7 









120 



21-8 









.. 



240 



6-2 







-- 



D. f. air 



4-4 



-- 



-'- 



•35 



15 



55' 



•1 



•43 



.. 



30 



113*5 



__ 







60 



86-7 













120 



55-0 











240 



38-8 







-- 



1). f. air 



31-3 



'- 



-- 



^* Abridged from the Report to the Carnegie Institution of Washington, 

 D. C. 



