RAIN AND ITS ORIGIN IN THUNDERSTORMS. 



405 



tions given to the air at the splashing of the water are not drawn into the Eber 



instrument, but give up their charges to the sides of the apparatus. 



The results of these experiments may be summed up in the following sentence : 

 When water drops are broken up in the atmosphere a separation of electricity 



takes place, the water becomes positively charged, and the air negatively charged ; 



and further, the amount of separation is independent of any charge previously on the 



drop. 



PART III. -Theoretical Conclusions. 



The consideration of the electricity of thunderstorms, which was the starting point 

 for the experiments just described, will now be resumed. It has been pointed out that 

 if the breaking of the raindrops in the air were accompanied by a separation of 

 electricity, this property might be the cause of the electrical effects observed during 

 thunderstorms, and it now remains to ascertain the extent to which . this suggestion 

 can be developed into a satisfactory explanation of the phenomena of thunderstorms. 



In order that the explanation may be satisfactory it is necessary to show 



(1) that there is a considerable breaking up of raindrops during a thunderstorm. 



(2) That the quantity of electricity which could be developed in this way is sufficient 



to account for the electrical effects observed. 



(3) That the general meteorological conditions which usually accompany thunder- 



storms agree with the explanation. 



Turning now to the first of these requirements, it will be shown that in all probability 

 the rainfall of thunderstorms is accompanied by considerable breaking up of large 

 into small drops. This can best be done by considering Prof. LENARD'S article 

 on " Rain,"* already referred to. 



Prof. LENARD made a number of experiments to determine the final velocity 

 attained by drops of water of different sizes when falling through air. His experi- 

 mental method was to create a vertical current of air and find the velocity of the 

 current which was just able to support drops of a given size. The following table 

 gives the results obtained : 



* LENARD, 'Met. Zeit.,' vol. 21, pp. 249-262, 1904. 



