HOT WINDS. 45 



that the knowledge we are gaining of the unknown past, as well 

 as the records of more recent years, point to the recurrence of 

 great fluctuations in the annual rainfall of this section, and it 

 seems probable that such changes follow series of years, and that 

 the recedence of our lakes may be followed by periods of higher 

 water. 



But the influence of the cultivation of the soil on water sup- 

 plies must be taken into account in this connection, for it is 

 undoubtedly true that man has changed the conditions of the 

 soil sufficiently to greatly influence the run-off. The breaking 

 up of large areas of prairie sod, with its low rate of evaporation, 

 and the planting of such land to agricultural crops with a rela- 

 tively high rate of evaporation, has resulted in a loss of soil 

 water. Then the cultivated soil takes up more water than the 

 sod-bound prairie slopes, so that it does not have so good an 

 opportunity to collect in lakes and swamps, which often supplied 

 the water of wells. And further, the straightening and cleaning 

 out of water courses', and the draining of swamps in the effort 

 to get arable land, has had a similar effect on subsoil water sup- 

 plies. 



HOT WINDS. 



The hot winds of the plains which so often cause serious 

 injury to farm crops in Kansas, Nebraska and the Dakotas have 

 been ascribed to the arid "staked" plains, whence, taking a north- 

 easterly direction, they draw all the moisture from the vegeta- 

 tion with which they come in contact. The view has also been 

 presented that they have their origin on the Pacific Coast, 

 ascend the Rocky Mountains, lose their moisture and descend 

 on the eastern slopes. But all theories that ascribe their origin 

 to a distant source are inadequate to explain their phenomena. 

 For instance, all who are acquainted with these winds know 

 that they blow only during very dry weather, when the earth is 

 heated very hot, that a good rain speedily brings them to an 

 end, and that they blow only during the daytime, commencing 

 about 9 A. M. and continuing until sundown. This daily move- 

 ment 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 which would require too 



