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



200 volts shows the presence of columnar or initial re- 

 combination. The curves of ionization coincide at about 

 600 volts ; the curves for the distribution of activity coincide 

 at about 1000 volts (not shown in the fig.), and thenceforth, 

 no increase of voltage alters perceptibly the percentage of 

 the cathode deposit. Thus there seems to be a definite limit 

 (94*9) to the value of the cathode percentage ; this 

 limiting value for actinium is considerably greater than 

 the value (88 - 2) found by Wellisch for the active deposit 

 of radium. 



The dotted lines in fig. 3 show a number of curves repre- 

 senting the variation with voltage of the ionization current 

 when various amounts of the emanation were in equilibrium 

 with the deposit products. The readings of the ionization 

 current were obtained while the air current was passing, and 

 on this account were not of a high order of accuracy as the 

 amount of emanation present in the vessel was subject to 

 slight variations. Hence a large number of these readings 

 were taken for various voltages and for different arbitrary 

 amounts of emanation used, and a set of average curves was 

 plotted. All the ionization curves in fig. 3 were plotted 

 by changing the scale of ordinates to correspond to a satura- 

 tion value of 94*9. It should be noticed that the ionization 

 current is assumed to attain its saturation value at 600 volts. 

 This is very approximately true ; at any rate the qualitative 

 results that will be drawn from the nature of the ionization 

 and activity curves are not invalidated by this assumption. 

 At 1000 volts ionization, current readings showed no appreci- 

 able difference from the values at 600 volts. 



From an inspection of the curves of fig. 3 it will be seen 

 that for any given amount of emanation the " activity yy 

 curve lies continually below the ionization curve. In other 

 words, the electric field is able to bring to the central 

 electrode a larger proportion of positive ions than of positively 

 charged deposit particles. For smaller voltages this can be 

 easily explained on the supposition that the deposit particles 

 and negative ions contained in the volume of the vessel com- 

 bine much more readily than the negative and positive ions 

 among themselves, i. e., volume recombination takes place at 

 a widely different rate for the two cases. 



The same remarks hold true in the case of columnar re- 

 combination also. The fact that the central electrode receives, 

 even for the higher potentials, a smaller proportion of 

 charged deposit particles than of positive ions shows that the 

 deposit particles are liable to lose their charge by recombina- 

 tion in the columns more readily than the positive ions. The 



