402 DR. G. C. SIMPSON ON THE ELECTRICITY OF 



rate of 20 volts per minute when a rapid blast of air was produced by the fan. This 

 rate of charging would have been increased if a large amount of fine spray had not 

 been carried from the apparatus by the air current. From the data that the system 

 had a capacity of approximately 180 cm. and the water ran out of the tubes at the 

 rate of 1200 c.c. a minute it will be seen that the charge given to the water was 

 approximately 10 X 10~ 3 electrostatic unit per cubic centimetre, i.e. a charge of the 

 same order of magnitude as that produced when individual drops were broken up 

 violently on a concentrated air jet. 



As the majority of the drops in this experiment after being carried upwards fell 

 back on to a pure water surface, the experiment was not entirely free from the Lenard 

 effect. In order to get over this difficulty the large vessel A fitted round the upper 

 rim of B was insulated from it. This vessel caught a certain amount of the fine 

 spray thrown up by the blast, and as the drops were exceedingly small and were 

 only just beginning to fall when they were caught, they struck the sides of the 

 vessel A without sufficient momentum to cause splashing ; it was therefore concluded 

 that very little separation due to the Lenard effect could take place at the impact. 

 The vessel B was then connected to earth, and A to a Wilson electroscope, and the 

 water and blast set into action. When the electroscope measured a definite potential 

 the blast and water were stopped, and the quantity of water caught in the vessel A 

 was run off and measured. 



The following shows the results obtained in a series of experiments in which rain- 

 water was used and the system was allowed to charge itself up to 9 volts before 

 measuring the water collected in A : 



Amount of water 

 caught in A. 



1st experiment 300 c.c. 



2nd 280 



3rd 290 



4th 230 



5th 265 



Mean 273 



Capacity of system = 135 cm. 



.'. Charge on 273 c.c. of water = ^ -els. units. 

 i.e. Charge per c.c. of water = 15X10~ 3 



Thus the charge per cubic centimetre of water is of the same order of magnitude as 

 that found when single drops were violently broken up on the air jet, and is only 

 slightly smaller in amount. From these experiments it would appear safe to 

 conclude that when pure water is broken up from large to small drops in the air 

 under ordinary conditions of temperature and pressure a ' separation of electricity 

 takes place. 



