Thirty-first Annual Meeting 199 
because of the processes just explained. The negative electrons 
in the meantime are carried up into the higher portions of the 
cumulus, where they unite with the cloud particles and thereby 
facilitate their coalescence into negatively charged drops. 
Hence, the heavy rain of a thunderstorm should be positively 
charged, as it almost always is, and the gentler portions neg- 
atively charged which very frequently is the case. 
‘*Such in brief, is Dr. Simpson’s theory of the origin of the 
electricity in thunderstorms, a theory that fully accounts for 
the facts of observation and in turn is itself abundantly sup- 
ported by laboratory tests and simulative experiments. 
‘Tf this theory is correct, and it seems well founded, it must 
follow that the one essential to the formation of the giant 
cumulus cloud, namely, the rapid uprush of moist air, is also 
the one essential to the generation of the electricity of thunder- 
storms. Hence the reason why lightning seldom if ever occurs 
except in connection with a cumulus cloud is understandable 
and obvious. It is simply because the only process that can 
produce the one is also the process that is necessary and suf- 
ficient for the production of the other.” 
4. Turbulence of the Cumulus Cloud. 
That the large cumulus clouds, especially those that pro- 
duce thunderstorms, are exceedingly turbulent within with 
violent vertical motion, as demanded by the theory just out- 
lined, is evident to even the casual observer. Furthermore the 
testimony of those balloonists who have had the trying ordeal 
of passing through the heart of a thunderstorm confirms the 
facts of observation. Since these are the only clouds, appar- 
ently, characterized by this high degree of turbulence, it may 
be well to pause a moment and ask why these motions— motions 
which, in the magnitude of their vertical components and 
degree of turmoil, are never exhibited by clouds of any other 
kind nor are they met with elsewhere by either manned, sound- 
ing or pilot balloons. Without going into very great detail, it 
may be pointed out, as has been done by von Bezold*, that 
the heat liberated by the sudden condensation from a state of 
supersaturation, and also from the sudden congelation of 
undercooled cloud particles, would cause @n equally sudden 
expansion of the atmosphere, resulting in turbulent motions 
analogous to those observed in the large cumulus clouds. 
