60 



S. G. LUSBY. 



not perhaps unreasonable to think that the greater the 

 number of ions in the air at any time, the greater will be 

 the rate of reproduction if those present are removed. In 

 the figure the observations with positive and with negative 

 ions are distinguished by the usual conventional signs. 







F 



igure I. 







100 













*> 



? CO 







+ ♦ 



- 





so 







- 







+ 

 * 











^.0 



♦ 

 " + 











in 



15 20 



Minutes. 



Time 



The relation between intervals of time from the removal of all 

 the large ions and the number of ions, expressed as a percentage 

 of the number originally present, reproduced in the intervals. 



The observations indicate that if all the large ions are 

 removed from the air at any moment, the number per unit 

 volume will gradually increase with time, until after an 

 interval of the order of 22 minutes it will be equal to that 

 of the ions originally present. 



For help with the earlier measures of the mobility I am 

 indebted to Mr. J. Ewing, b.sc. 



