66 ROYAL SOCIETY OF CANADA 



One of the main questions left open in the present investigation is 

 the cause of the decrease in activity of the electrodes in the three dif- 

 ferent gases at the low pressures. 



It seems fair to conclude from the results that in the region of low 

 pressures there was a gradual decrease both in the excess of positively 

 charged deposit particles and also in the total number of the particles 

 present in the space between the electrodes. 



The experiments, however, do not show whether this decrease was 

 due to a falling off in the amount of emanation coming into the space 

 between the electrodes or to the emanation and deposit particles passing 

 directly through this space into the outer chamber of the apparatus. 

 From the fact that at the low pressures as well as the high ones the 

 activity fell away as the distance of the salt from the electrodes was 

 increased it would seem that- the decrease mentioned above was due to a 

 decrease in the amount of emanation entering the space between the 

 electrodes. The matter, however, is not clear and consequently the ex- 

 planation of the decrease must be deferred until the scope of the in- 

 vestigation can be extended. 



In conclusion I desire to thank Professor McLennan for the selec- 

 tion of the subject, and for the yery helpful suggestions he has offered 

 from time to time during the investigation. . 



