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



never, in the regions of the storms in which violent and frequent lightning discharges 

 occurred. 



It will sometimes happen that the negatively charged cloud will be carried by the 

 upper winds to some distance from the place where the separation of electricity was 

 effected and will then give rain. In such cases, rain charged with negative electricity 

 would be likely to occur. The frequency with which negative electricity was 

 observed by ELSTER and GEITEL with rain associated with distant thunderstorms 

 might be explained in this way. 



If the ascending current keeps a considerable amount of the highly charged water 

 in suspension, and the negative electricity is held in the cloud above, it is very 

 probable that the main lightning discharges would take place from the accumulated 

 water at the head of the ascending current to the charged cloud above. This 

 would explain the observation that most lightning discharges pass within the 

 thundercloud from base to summit. 



Falls of hail are frequently associated with thunderstorms, and hailstones as has 

 already been pointed out can only form if they are supported during formation 

 by strong ascending currents. Further, the structure of a hailstone indicates that it 

 is often carried up and down past the zero isothermal. Now, a current of air 

 sufficiently strong just to support a hailstone as big as a pea would be more than 

 sufficient to carry up the water it condenses within itself; hence, hailstones would 

 always have a greater downward velocity relative to the ascending current than the 

 water in the current, and there would be a large amount of splashing between 

 the two. There would be, consequently, a much greater amount of separation 

 of electricity than would have taken place without the hailstones, and this 

 might very well account for the great violence of the electrical discharges in hail- 

 storms. 



The observations made by Mr. CLAYDKN* on the formation of thunderclouds seem 

 to me to be in entire agreement with the general disposition of air currents required 

 for the theory here proposed. 



The present discussion is confined to the electrical phenomena of thunderstorms, as 

 I have not yet collected data which are sufficient to allow me to decide whether in 

 steady rain such as accompanies ordinary depression, positive or negative electricity 

 predominates. It is quite conceivable that the charge brought down under such 

 conditions is due to causes entirely different from those which produce the excessive 

 electrical separation in thunderstorms. For similar reasons the electrical phenomena 

 connected with snowstorms have not been considered. Until all these effects have 

 been studied it is not possible to discuss the bearing of my observations on the general 

 problem of atmospheric electricity. 



The investigation of vertical air currents during a thunderstorm would have an 



* Loc. tit,, pp. 109,110. 



