404 



DE. G. C. SIMPSON ON THE ELECTRICITY OF 



the air in that period. Drops were then allowed to fall from the tube D on to the jet, 

 and two more readings of the electroscope were taken with intervals of 10 minutes 

 between them, and the number of drops which had fallen in that time was noted. The 

 difference of the results of the two experiments gave the amount of electricity imparted 

 to the air by the breaking of a known number of drops, and from this the amount due 

 to the breaking of a single drop was calculated. Similar experiments were made with 

 the central cylinder of the Ebert apparatus charged both positively and negatively. 

 The results are shown in the following table : 



TABLE XV. 



Now, as the capacity of the Ebert apparatus was 14 els. units 

 The mean negative iouisation caused by the 

 breaking of one drop 



= " = 0'0033 els. unit. 



- = O'OOll els. unit 



The mean positive ionisation caused by the 



breaking of one drop ....... 



Excess of negative ionisation caused by the 



breaking of one drop ....... = 0'0033 O'OOll = 0'0022 els. unit. 



The results of these experiments are interesting, in that they show 



(1) The breaking of drops of water is accompanied by the production of both positive 



and negative ions.* 



(2) That three times as many negative ions as positive ions are released. 



The difference between the negative and positive charges produced should correspond 

 to the charge remaining in the water. Now, it has been shown above that 5 - 5X 10~ 3 

 els. unit of positive electricity is retained by the water of each drop after breaking, 

 and this amount agrees as well as could be expected with the 2'2XlO~ 3 els. unit 

 per drop found in the air ; the difference is no doubt due to the fact that many of the 



* This experiment does not indicate the nature of the ions produced : for instance, the positive ions 

 might be exceedingly fine water drops. Still it shows that something of the nature of ordinary ionisation 

 takes place and that the ions exist long enough to be separated by the Ebert instrument. 



