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



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 aitd 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 



