C. Barus — Decay of Ionized Nuclei. 419 



Art. XXXVII. — The Decay of Ionized Nuclei in the Fog 

 Chamber, in the Lapse of Time / by C. Barus. 



1. Introduction. — The attempt was made in an earlier 

 paper to standardize the coronas by aid of the decay curves of 

 radium. The method is apparently very simple 'and requires 

 the knowledge merely of the coronas appearing under given 

 circumstances when the radium tube is in place d on the out- 

 side of the fog chamber, in comparison with the coronas 

 observed under the same circumstances when the radium has 

 suddenly been removed for different lengths of time before 

 condensation. From electrical observations with condensers, 

 the equation 



dn/dt=—bri i or \Jn = l/n' + b (t— i') 



is found to be adequate if n and n' denote the ionizations occur- 

 ring at the times t and t', and the same would appear to be the 

 case with the corresponding nucleations. Moreover, if the 

 relative nucleations for two coronas obtained at a given 

 exhaustion are known (for instance by the earlier method of 

 geometric sequences) the absolute values of the nucleations 

 will follow. With a radium ionization at t and t' seconds after 

 its removal 



£-')w-o- 



But the attempt to carry out this apparently straightforward 

 method leads to grave complications. If n be reckoned in 

 thousands per cubic centimeter, the electrical value of b may 

 be taken as of the order of b = "001 ; while the value of b 

 which I deduce from the decay of ions in the fog chamber, is 

 more than two times as large as this, increasing moreover very 

 rapidly as the nucleation is smaller. True it is possible that 

 the method for finding the nucleations, absolutely, may be at 

 fault. If relative values seem to be trustworthy, absolute 

 data are not to the same degree substantiated ; but even if this 

 were granted, however improbable, the march in the values of 

 b would be unaccounted for and seems to be a new phenome- 

 non. 



2. Data. Exhaustion above the fog limit of air. — In the 

 first series of experiments the adiabatic drop of pressure hp 

 was somewhat larger than the condensation limit of dust free 

 wet air. The initial coronas were small as the radium was 

 weak (10,000X, 100 mg). 



When the values of b were computed from the means of 

 •successive pairs of measurements of nucleation n, at different 



