202 Proceedings of the Ohio Academy of Science 
while it is safe to say that the thunderstorm, in one form or 
another, does occur at some time or other in all parts of the 
earth, yet from what we know of the meteorological conditions 
ordinarily prevailing over the various portions of the earth, we 
are very sure that it is very rare over large areas and may 
never occur in some regions. In the United States®, for exam- 
ple, we find two centers of maximum thunderstorm activity, one 
over Tampa, Florida, and the other over Santa Fe, New Mexico. 
In the ten-year period, 1904-1913, 944 thunderstorms were 
recorded at Tampa and 710 at Santa Fe. Tampa is near sea- 
level and Santa Fe is about 7,000 feet above the sea. 
7. Classification of Thunderstorms. 
One is impressed with the very great variety and many 
variations met with in the study of these storms. This is true 
whether one is considering the attendant circumstances, the 
varying degree of intensity exhibited by them, the frequency of 
occurrence, the resulting effects, the distribution through the 
day, the year, or over the earth’s surface, or whether one is 
considering the factors operating to produce and maintain 
these storms. Variety everywhere! 
At one time, and not so long ago, it was thought that all 
thunderstorms were local phenomena and were therefore not 
subject to any general law. In an important sense the thunder- 
storm is a local phenomenon but the forces operating to pro- 
duce many of them are far from local. It is now known that 
a majority of these storms travel in a definite direction and 
are therefore moving under a general law. In general, with 
respect to the producing causes or conditions out of which 
they grow, thunderstorms may be divided into (1) local or 
‘‘heat’’ thunderstorms, and (2) the cyclonic thunderstorms, or 
‘“‘thundersqualls.’’ Or, if we wish to be a little more exact or 
‘‘scientific,’’ we may follow Professor Humphreys and make 
five classes, namely, (1) the ‘‘heat”’ or local, (2) the cyclonic, 
(3) the tornadic, (4) the anti-cylconic, and (5) the “border,” 
thunderstorm. The significance of this classification will be 
pointed out later in connection with the illustrated portion of 
this lecture but it seems appropriate at this time to refer to 
Durand-Greville’s famous theory of ‘‘the squall zone”’ in con- 
nection with cyclonic thunderstorms. He holds that ‘cyclonic 
thunderstorms’’—and that means all except the ‘“‘local’’ or 
