HOT WINDS. 39 



showing that there is evidently some connection between them 

 and the course of the sun. For these reasons and others 

 which would require too much space to give them here, the 

 best authorities unite in attributing- them to local origin. 



Mr. George C. Curtiss describes the process of the produc- 

 tion of a typical hot wind as follows: "The necessary condi- 

 tions are those of the 'warm wave,' namely, a diminishing 

 pressure to the northward, producing southerly winds which 

 initially elevate the temperature above the normal. A cloud- 

 less sky favors an intense insolation, as a result of which the 

 dry ground is soon raised to an extreme temperature, and the 

 air is heated from it by radiation, reflection and conduction. 

 The resulting diminution of density due to the rise of tempe- 

 rature furnishes impetus to previously existing horizontal 

 currents, and by 10 o'clock in the morning the hot wind is 

 fully developed. Hundreds of miles of hot dry earth contrib- 

 ute to maintain and feed the current, and gathering strength 

 as the sun mounts higher the hot wind sweeps over the 

 defenseless prairie. Neither hills nor forests rise in its path 

 to break its power or dispute its sway and with no enemy save 

 the tardy raincloud, the fetid blast sucks out the life-sap of 

 the growing grain. It will be readily seen then that each of 

 tne states, Kansas, Nebraska and North and South Dakota, 

 develops its own hot winds and cannot charge them to the 

 account of its neighbors." 



The local origin of these winds at once suggests the 

 desirability of frequent windbreaks on the prairie farms as 

 offering the most practical way of breaking them up. Irriga- 

 tion of large areas will also undoubtedly do much to prevent 

 them. 



