318 The Farm Woodlot 



This daily movement is often constant for several weeks, 

 showing that there is evidently some connection between 

 them and the course of the sun. For these reasons, and 

 others, the best authorities unite in attributing them to 

 local origin. 



George C. Curtiss describes the process of the production 

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

 ditions 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 cloudless 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 temperature 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 contribute to maintain 

 and feed the current, and gathering strength as the sun 

 mounts higher, the hot wind sweeps over the defenceless 

 prairie. Neither hills nor forests rise in its path to break 

 its power or dispute its sway, and with no enemy save the 

 tardy rain cloud, the fetid blast sucks out the life sap of 

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

 of the states, Kansas, Nebraska and North and South 

 Dakota, develops its own hot winds and cannot charge 

 them to the account of its neighbors." 



Since, then, these hot winds are of such origin, it is 

 clear that windbreaks at frequent intervals on the prairie 

 farms would prevent their formation. The increased 

 humidity of the air in the immediate neighborhood of the 



