8 BULLETIN 297, U. S. DEPAETMENT OF AGKICTJLTURE. 



the latter month being 6.5 miles. The greatest seasonal velocity was 

 recorded in 1911, which was the year of least rainfall and greatest 

 evaporation. The highest average velocity for the entire period was 

 recorded in May of that year, 11.6 miles per hour. The average 

 velocity for both June and July was also unusually high. The low 

 yields in 1911 were due to the combination of very low rainfall, high 

 evaporation, and injury to crops from high winds. The wind for any 

 one day (24 hours) seldom exceeds a total of 500 miles, while for any 

 one day during June and July it is usually much less than 250 miles. 



TEMPERATURE. 



The temperatures at the Belle Fourche Experiment Farm are 

 recorded throughout the year by means of maximum, minimum, and 

 dry-bulb thermometers. A summary of the mean, maximum, and 

 minimum temperatures from April to July, inclusive, for the six years 

 from 1908 to 1913 is presented in Table VI. 



Table VI. — Mean, maximum, and minimum temperatures at the Belle Fourche Experi- 

 ment Farm, by months, from April to July of each year, 1908 to 1913, inclusive. 



[Data (in °F.) from the records of the Biophysical Laboratory of the Bureau of Plant Industry.] 





April. 



May. 



June. 



July. 



3 



Year. 



c 



a'. 



3 



S 



V. 



6 

 3 

 6 

 .3 



i 



a 



3 







C3 

 3 



a 



J 



8 



s 



c 



C3 

 CO 



a - 



3 

 S 

 S 



c3 



a 



3 

 S 



a 



i 



o 



a 



3 



a 



X 



3 



a 



3 

 S 

 = 



C3 



i 



S 



1908 



48 

 38 

 51 

 43 



47 

 48 



89 

 73 

 89 

 88 

 78 

 89 



5 



6 

 24 

 13 

 22 



24 



52 

 52 

 52 

 58 

 55 

 53 



79 

 84 

 81 

 94 

 84 

 95 



29 

 22 

 27 

 23 

 32 

 26 



63 

 66 

 68 

 73 

 66 

 66 



90 

 95 

 108 

 101 

 101 

 98 



39 

 45 

 36 

 43 

 39 

 45 



73 

 70 

 76 

 71 

 70 

 70 



100 

 100 

 109 

 105 

 94 

 101 



43 

 41 

 44 

 41 

 40 

 42 



59 



1909 



56 



1910 



62 



1911 



61 



1912 



60 



1913 



59 









46 



84 



16 



54 



86 



26 



67 



99 



41 



72 



101 



42 



59.5 







Table VI shows that the highest average mean, maximum, and 

 minimum temperatures have been recorded in July, though the maxi- 

 mum and minimum temperatures are only very slightly higher than 

 those recorded in June. During the six years, frost has not occurred 

 in June, the lowest minimum temperature recorded being 36° F. 

 This table shows that the average mean temperature for the growing 

 season for cereals for the six years is 59.5 ° F. The greatest variation 

 from this average in any one year was in 1909. when the seasonal 

 mean was 56° F. 



The temperature of western South Dakota is somewhat higher than 

 that of corresponding latitudes in the eastern part of the State. This 

 is shown in Table VII, in which the mean monthly and annual tem- 

 peratures at Newell, Camp Crook, Aberdeen, Pierre, and Brookings 

 are given. Camp Crook is near the northwestern corner of the State, 



