C. Barus — Standardization of the Fog Chamber. 89 



With still higher nucleations N — 570,000 the data were 

 Y — -123 volts, V — '90 volts, the field being 1-2 volts per 

 cm, V/V = -137 and 10 10 e = 34 electrostatic units. Thus it 

 follows that both positive and negative ions must have been 

 caught in the fog chamber. 



4. Other Equations. — The available equations if I be the 

 electrical current in the condenser, for which the nucleation 

 in the annular volume v is n, while i\ 7 is the nucleation in the 

 fog chamber without current, h being the coefficient of the 

 decay, are (apart from secondary radiation) 



-n=b(N*-tf)-I/ev, (1) 



1= GV, (2) 

 where Ci$ the capacity of the system, 



1= 27rln UVef(\ogRJB^) (3) 



where F/T^is constant for very small voltages. Hence there 

 would be a second method of reaching e in terms of h, or the 

 reverse, if equation (1), where / is essentially a function of 

 time, were integrable. Nevertheless the equation is available 

 at once if V is laro;e enough to make the current constant. 

 In this case one may write, if JV nuclei are found in the fog 

 chamber without electrical current, while n occur in the con- 

 denser with current, 



e = CVj (300tt {B^-B^lb^-n 2 )). 



Here n must be negligible compared with iV r . Values so 

 obtained (an Exner graduated electroscope suffices) are quite 

 consistent among themselves ; but the data come out 20 to 30 

 too large if h = 1'lXlO" 6 is assumed. 



Installing a plate condenser in the fog chamber, I noticed 

 that for a charge of 100 or 200 volts the coronas between the 

 condenser plates were of about the same character as the 

 coronas without, while the large chamber is filled with ions at 

 the highest voltages. Possibly therefore such ionization as 

 reaches the inside of a condenser by diffusion may account for 

 the excessive currents ; or there may be increased production 

 due to secondary radiation. It is interesting to note that 

 potentials of 100 to 200 volts are sufficient to eject dust par- 

 ticles from the condenser, very small and not numerous it is 

 true, but sufficient to make it possible to catch all the ions 

 only after these dust particles have been precipitated in one 

 or more exhaustions.* 



5. Conclusion. — The good values of e obtained under 

 widely varied conditions in the present very rough experi- 

 ments, show that the present method is not unworthy of 

 development, with a view to the further measurement of this 



*The complicated conditions encountered here will be restated elsewhere. 



