C. Bar us — Decay of Ionized Nuclei. 421 



If we combine the first observation with the fourth, etc., as 

 before, and 



Sp/p = x= -27, b = -0038, 

 041, 

 <)57, 

 134, or a mean value of b = '0045 



(when n is reckoned in thousands), if the last observation is 

 ignored. But to ignore this value is here quite inadmissible, 

 as the data for a parallel series where x = "25, viz., 



b = -02 1 

 •177 

 fully show. 



4. Data for weak ionization. Radium at a distance. — 

 In the above work the initial intensity of radiation was the 

 same. It was suggested that the average size of a nucleus 

 might decrease in the lapse of time. Thus a variety of further 

 questions arise ; 1, whether weak radiation produces a smaller 

 average nucleus ; 2, whether a stronger radiation does the 

 reverse ; 3, whether the limit of b decreases as the exhaustion 

 increases and finally approaches b = "001 (counting n in thou- 

 sands), etc. The experiments of the following work show that 

 b varies with the number of nuclei present, no matter whether 

 a given nucleation is due to weak radiation, or to decay from 

 a stronger radiation, or finally to low exhaustion ; or that the 

 nuclei probably break to pieces as a whole. 



The data, moreover, were investigated by the new method of 

 two diffraction sources of light, 8 cm. apart, at a distance It 

 from the fog chamber. The number of nuclei, n, found in the 

 exhausted fog chamber, is corrected by multiplying by the 

 volume expansion. Finally, b was computed from pairs of 

 observations about 20 seconds apart. Water nuclei were 

 always precipitated before each test. "With the exhaustion 

 slightly above the condensation limit of air, the data were 

 constructed, in comparison with cases for stronger radiation 

 and of weaker radiation (by decay) in the above experiments. 

 Together they formed a coherent series of curves, proving 

 that it is the number n present which determines the value of 

 b, no matter whether the small number is due to low exhaus- 

 tion ($%>/]) near the condensation limit), or to decay of ions in 

 the lapse of time (exhaustion t seconds after removing the 

 radium from the fog chamber), or due to lower radiation 

 (radiation at some distance 40 em , from the fog chamber.) 



The results may be otherwise summarized, by giving 

 — b = {dn/dt)/n~ in terms of the nucleation n, from which the 

 decay takes j^lace. The rapidly increasing values of b when n 

 is smaller and their tendency towards constant values when n 



