428 Prof. E. M. Wellisch : Experiments on 



emanation decays beyond a certain value. In Table I. the 

 amount of charged gas activity is approximately proportional 

 to the quantity of emanation in the vessel as measured by 

 the saturation current (cf. 2, 16, and 19). If in Table II. 

 we calculate the ratio of the gas activity obtained with 

 1 minute exposure and —160 volts to the saturation current, 

 we obtain for the five successive days the following numbers: 



9-65, 9-74, 7-90, 2'62, -50. 



A careful examination of all the results obtained indicates 

 that the proportion of charged deposit present in the gas 

 contained in the cylindrical vessel without a central electrode 

 remains approximately constant over a wide range ; but 

 when the emanation has decayed until the saturation current 

 obtained when a central electrode is introduced is about 

 5*0 X 10~ 9 ampere, this proportion suffers a sudden diminu- 

 tion in magnitude. A current of 5*0 x 10" 9 ampere implies 

 the production of 3'23 X 10 10 pairs of ions per second in the 

 vessel, and as the volume of the vessel was 326 c.c. the 

 number (q) of ions produced per c.c. per second is approxi- 

 mately 10 8 . If we assume that the value of the coefficient 

 of recombination (a) is unaltered by the presence of the 

 emanation, and take for a the value assigned by Townsend, 

 viz., 3400 Xe, then the number of ions of each sign present 

 per c.c. in the vessel is s/q/a =7*95 x 10 6 . 



When the density of ionization in the gas falls below this 

 amount, there seems to be a rapid diminution in the amount 

 of charged activity in the gas. When the emanation decays 

 still further, the active deposit particles in the gas appear to 

 be uncharged and in amount to be a constant fraction of the 

 total amount of deposit in equilibrium with the emanation. 

 It appears from the results that aggregation of the deposit 

 particles ceases fairly abruptly at the critical stage, but there 

 is also evidence that a considerable fraction of the deposit 

 particles in the gas can still be charged even after they have 

 ceased to aggregate. Aggregation implies a slow rate of 

 diffusion, which is made manifest by the very small amount 

 of deposit collected on a central rod in the absence of an 

 electric field. It is easy to tell, by measuring the propor- 

 tionate activity collected on such a rod, the stage when 

 aggregation practically ceases. As stated before, aggrega- 

 tion ceased fairly abruptly when the saturation current was 

 5*0xl0~ 9 ampere, but evidence at any rate of negatively 

 charged deposit particles in the gas was found even with the 

 current as low as 10" 9 ampere. 



The general effect seems to be that the active deposit 



