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 WilUston, 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 

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



ao 



^'f i| 



llllllll 



mm 





1900 



1905 



1910 



1915 



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



