208 Proceedings of the Ohio Academy of Science 
the place of observation. Then besides the thunderstorm is of 
a very limited duration; it may, at the very most, last twenty- 
four hours, but as a rule a very few hours will exhaust it. It is 
only when this type of storm assumes the character of a tornado 
that knowledge of its approach becomes really important. 
10. The Thunderstorm and Excessive Precipitation. 
Another thing that gives to the thunderstorm economic 
importance is the fact that from 66 to 100 per cent of all 
instances of excessive precipitation in the United States occur 
as the result of or in connection with thunderstorms’. Some 
places, like Bismark, Denver and Sante Fe, excessive precip- 
itation never occurs except in connection with thunderstorms. 
Furthermore, the records will show that practically all cases of 
remarkable downpours of rain or hail occur in connection with 
these storms. 
II. THUNDERSTORMS IN OHIO. 
1. Introduction. 
Needless to say, the thunderstorms of Ohio do not differ 
in any essential respect from those we have been discussing. 
Our chief and perhaps only excuse for referring to them at 
this time and in this manner is to make an occasion to call the 
attention of the Academy to a piece of work accomplished in 
Ohio that, so far as we know, is the only one of its kind in this 
or any other country, namely an intensive study of thunder- 
storms over a limited region through a period of one year. The 
purposes were to determine as far as practicable the origin, 
the distribution, the number, the frequency, the extent of 
territory covered, the attending phenomena, etc., of these 
storms, and if possible, trace the history of each individual 
thunderstorm that entered or originated in the state of Ohio, 
during the year 1917. 
2. The Plan. 
Our plan was to secure at least one observer in each town- 
ship in the State but as the work was to be purely gratuitous 
we were not able to interest one person in each of the 1357 
townships. Our total enlistment was about 730 volunteer 
