24 WILLIAM H. ALEXANDER Vol. XXII, No. 1 



features of the thunderstorm. It is always evident in the 

 turbulent cauliflower heads of the cumulus cloud, the parent, 

 presumably, of all thunderstorm. Besides, its inference is 

 compelled by the occurrence of hail, a frequent thunderstorm 

 phenomenon, whose formation requires the carrying of rain- 

 drops and the growing hailstones repeatedly to cold and there- 

 fore high altitudes. And from the existence of hail it is further 

 inferred that an updraft of at least eight meters per second 

 must often occur within the body of the storm, since, as exper- 

 iment shows, it requires approximately this velocity to support 

 the larger drops, and even a greater velocity to support the 

 average hailstone. 



"Experiment also shows that rain can not fall through air 

 of ordinary density w^hose upward velocity is greater than 

 about eight meters per second, or itself fall with greater 

 velocity through still air; that in such a current, or wdth such 

 a velocity, drops large enough, if kept in tact, to force their 

 way dowm, or, through the action of gravity, to attain a greater 

 velocity than eight meters per second with reference to the 

 air, w^hether still or in motion, are so blown to pieces that the 

 increased ratio of supporting area to total mass causes the 

 resulting spray to be carried aloft or left behind, together 

 with, of course, all original smaller drops. Clearly, then, the 

 updraft s within a cumulus cloud frequently must break up at 

 about the same level innumerable drops which, through 

 coalescence, have grown beyond the critical size, and thereby 

 according to Simpson's experiments, produce electrical sep- 

 aration within the cloud itself. Obviously, under the turmoil 

 of a thunderstorm, its choppy surges and pulses, such drops 

 may be forced through the cycle of union (facilitated by any 

 charges they may carry) and division, of coalescence and dis- 

 ruption, from one to many times, with the formation on each 

 at every disruption, again according to experiment, of a corre- 

 spondingly increased electrical charge. The turmoil compels 

 mechanical contact between the drops, whereupon the charges 

 break down the surface tension and insure coalescence. Hence, 

 once started, the electricity of a thunderstorm rapidly grows to 

 a considerable maximum. 



"After a time the larger drops reach, here and there, places 

 below which the up-draft is small — the air can not be rushing 

 up everywhere — and then fall as positively charged rain, 



