Frequency and Length of Drought 



109 



is unfortunate that we are unable to present closely comparable 

 data for more than the years 1894, >95, '96 and '97, and even for 

 these years only for corn. As for other crops in the different 

 years, they were grown on different soils ; but bringing the yields 

 of dry matter of maize per acre into comparison with the rainfall 

 conditions under which they were produced, we shall have the 

 table which follows : 



Table showing the relation of yields of dry matter per acre to the quantity and 

 distribution of rainfall 



Yield of dry 

 matter per acre Aggregate No. of inches of rainfall 



Year Periods 



/ No. of rainfall periods 



1894 



1895 



1896 



1897 



\ Length 



\ Length 

 /No. of 

 \ Length 

 /No. of 

 \Length 



4 , 



days 



O.OOO 



1.401 



4.145 



3.405 



If the rainfall in 1896 and in 1894 is compared with that in 

 1895, when there was a very much smaller crop, it will be seen 

 that the number of rainfall periods in 1895 is decidedly less, while 

 the length of them is much greater. It was this much longer 

 interval of time intervening between like quantities of rain which 

 determined the small yield ; and it is this character of the rain 

 of humid climates which so seriously cuts down the average 

 yields per acre, and which makes it possible for the methods of 

 irrigation to give such constant and such large yields wherever it 

 is well practiced in arid climates. 



Taking the best year of the four, 1896, it will be seen that 

 the average length of periods of 1 inch of rainfall was 7 days, 

 and there were 26 of them in the six months, making about as 

 uniform distribution of rain as is likely to occur in humid cli- 

 mates ; but there were in this season 1 period of 10 days, 3 

 periods of 11 days, 2 periods of 12 days and 2 periods of 13 days' 

 duration with but 1 inch of rain, which are too long in Wisconsin 



