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easily see how the air from the western plains will pour down 

 into this barometric trough to equalize the pressure. The data 

 gathered so far is not sufficient to warrant the conclusion that 

 the prolific cause of our tornadoes, during May and June, is the 

 inrush of these western cold, dry currents to the partial vacuum 

 of the barometric trough, yet we have enough data on which to 

 ground such an assumption. But when we come to consider 

 the effect of these winds in the midsummer months, when, in 

 their passage over the arid plains, they have changed their 

 character from cold and dry, to hot and dry, we stand on surer 

 ground. We know that when these winds join with the vapor 

 laden air currents from the south, four effects are produced. 



First — A change of direction of the combined currents from 

 south and west to the northeast. 



Second — A diffusion of the vapor borne on the southern cur- 

 rent among the hungry air from the west. 



Third — A general lifting of the combined currents by the 

 great increase of heat from the western current. 



Fourth — This increase of heat gives the combined current a 

 firmer grip on its moisture and floating higher, as we have seen, 

 enables it to carry this moisture further to the northeast, causing 

 excessive drouths along its route. 



Is there any way to change this condition? 



There is a remedy, simple and practical; but from the nature 

 of the case, immense in its application, and to succeed must de- 

 pend wholly on the intelligent, comprehensive co-operation of 

 the states interested. These western winds must be tempered 

 with moisture. But how? We have seen that their natural 

 base of supply for moisture is the Pacific ocean; that in their 

 passage eastward they leave a great amount of this moisture, in 

 the shape of snow-fall, along the crests of the Rocky mountains. 

 This snow-fall must be utilized for irrigating purposes along the 

 eastern slopes of these mountains. This is 



THE PLAN OF ATTACK. 



on the western side of the arid region. The instrumentality on 



