766 Dr. A. N. Lucian on the Distribution of the 



the potential was applied and the air current regulated to 

 the desired pressure. This method was followed in all the 

 experiments, and evidently insured a perfectly dry and dust* 

 free stream of emanation flowing into a dust- and moisture- 

 free vessel. The electrode and the vessel were thus exposed 

 to a steady flow for a period long enough for the emanation 

 to get into equilibrium with its subsequent products. This 

 period of activation was usually three hours, and never less 

 than two and a half hours. 



When equilibrium was established, measurements were 

 taken of the ionization current passing through the vessel, 

 first with the potential (y) used in the particular experiment 

 and then with a standard potential, which was 600 volts in 

 ail cases. These ionization currents are designated by I v and 

 I 60 o respectively. These operations in general disturbed the 

 activity distribution : hence after the ionization readings 

 ample time was allowed for this distribution to be restored. 

 Then the actinium tube was removed, the electric field was 

 switched off, and a strong current of dry air allowed to flow 

 for a minute in order to drive out the emanation and deposit 

 particles remaining in the vessel. Time was measured from 

 the instant of the removal of the actinium tube. 



The amounts of deposit which settled on the case and the 

 central electrode were measured by the ionization current to 

 which they gave rise, with an applied potential of +200 volts 

 on the case. Although this potential was not sufficient to 

 afford saturation current, later experiments showed that the 

 ratio of the activities thus measured was the same as that 

 obtained by using higher potentials. To measure the case 

 activity, the ebonite plug P containing the central electrode 

 was removed, care being taken that the electrode did not 

 touch the sides of the vessel, the gauze bottom was removed 

 and a clean flat bottom was screwed on, to avoid spurious 

 effects due to deposit particles collected by the cotton-wool. 

 Then a fresh electrode held in a stiff brass rod, without the 

 ebonite plug, was introduced into the vessel and held as usual 

 by the brass clip H ; and a series of readings of ionization 

 current were taken at definite intervals after the zero of 

 time. It is to be noticed that by avoiding the use of ebonite 

 the ionization current could be measured with great precision. 

 As the case activities were in general small, their exact value 

 was of relatively greater importance than those of the central 

 electrode ; hence a greater number of readings were taken 

 with and without the capacity C in order to check the results. 

 It might be mentioned that almost all the readings were 

 taken with the capacity added to the system. From these 



