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the former. The drops in a thundercloud are, therefore, 

 carriers of small charges of electricity, and by the violent 

 action of the wind undergo disruption at one instant and 

 coalescence at another, which makes for electric separation 

 and accumulation. 



Dr. Simpson was led to this conclusion by an experiment 

 in which drops of distilled water were caused to fall through 

 a vertical blast of air that was sufficiently strong to break 

 up the drops into spray, which gave the following results : — 



1. That 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. 



According to Professor W.J. Humphreys rain cannot fall 

 through air of ordinary density the upward velocity of which 

 is greater than 8 meters per second, and if the raindrops are 

 of such a size as to drop by gravity, or be suspended in the 

 face of such a current, they are so blown to pieces that the 

 spray is carried aloft, and, in this way, there is caused an 

 electrical separation within the cloud. This electrical separa- 

 tion places a heavily-charged positive layer (within the lower 

 portion of the cloud) between the negatively-charged earth, 

 below, and a much higher, heavily-charged negative layer 

 in the upper portions of the cloud. In such a condition of 

 electric tension it is easy to understand why an electric dis- 

 charge, by lightning, should take place, either between 

 respective clouds or between the positively-charged cloud and 

 the earth. 



Formation of Hail. 



When a powerful convection current is established the 

 uprush of warm air may be carried beyond the normal height 

 at which the cumulus cloud usually floats in the atmosphere. 

 According to Humphreys it is only beyond the 4-kilometer 

 level that freezing temperatures are reached. Aqueous 

 vapour, and perhaps the finest spray, form snow or frost, 

 while the liquid drops congeal to ice. Should the upward 

 rush of air slacken, or should the pellets of hail get outside 

 the limits of the rising column of air, they would begin to 

 descend. Reaching lower altitudes they would probably 

 become coated with fresh moisture, and being caught in 

 another furious gust of wind would be once more carried up- 

 ward, together with much rain-spray, to the colder region. 

 Here the hailstone, with its accrued moisture and possible 

 union with the finer spray, gathers an additional coating of 

 snow or ice. Such alternations in movement may occur several 

 times in the development of a hailstone, and is possibly 

 limited only by the increasing weight of the hailstone, which 

 finally brings it down to the ground. 



