AGRICULTURAL PRACTICE AND CLIMATIC CYCLES. 



267 



(fig. 16) shows five 2-year and two 3-year cycles since 1900, while the record 

 since 1885 shows an almost complete series of 2-year cycles. The Cheyenne 

 graph shows a preponderance of 3-year cycles, and with the exception of a 

 single year (1908), there is a perfect succession of 2-year and 3-year cycles. 

 At Akron the first two cycles are 2-year and the last three are 3-year. At 

 Amarillo the cycles are much less distinct, but the 3-year cycle is fairly well 

 marked, especially in the seasonal rainfall. A comparison of the respective 

 graphs will disclose the regional rainfall balance during a particular year. 

 The year 1905 was excessively wet at Amarillo, Akron, and Cheyenne, but 

 was very dry at Williston, 1906 being the wet year. Likewise, a slightly less 

 wet year (1915) was excessively wet at Amarillo and Akron, only a little above 

 the normal at Cheyenne, and slightly below normal at Williston, the excess 

 falling the next year again. The year 1911 was the driest of the record at 



ao 



Illiillfl 



i M M 1 1 1 M ■ i 



1900 1905 1910 1915 



Fig. 19. — Graph of total and seasonal rainfall at Amarillo, Texas. 



