434 KANSAS CITY REVIEW OF SCIENCE, 



sand feet before they have had time to feel the heating effect of the land which is 

 here very slight; and the precipitation is thus very^ copious. Descending to 

 lower levels inland they soon become dry and produce a sub-arid climate. 



The most frequent variants of climate are the great differences of altitude in 

 different portions of the west. The mountain tops and summits of the plateaus 

 are always well watered, and in any given latitude the rainfall increases or di- 

 minishes at a fairly definite rate with the altitude. But the variation of rainfall 

 with altitude is by no means a simple ratio. Between 4500 and 6000 feet the 

 difference in rainfall is not great; between 6000 and 7500 feet it is very consider- 

 able; between 7500 and 9000 it is still greater. 



Moreover the rainfall is greater, ceteris paribus, in high latitudes than in low 

 latitudes. In passing from the southern to the northern boundary, if we com- 

 pare localities of equal altitudes along any given meridian, we shall find the rain- 

 fall steadily, though perhaps not uniformly increasing. This is an obvious conse- 

 quence of the theory suggested. 



Although no very great effects upon the general condition of aridity are here 

 attributed to the depletion of moisture by the passage of the winds over mountain 

 ranges, it is still true, no doubt, that highly important local effects are thereby 

 produced. The rainfall at the eastern base of the Sierra Nevada, and for two 

 hundred miles east of it, is most probably reduced very greatly by this cause. 

 In the sink of the Humboldt River, the annual precipitation seldom reaches four 

 inches, and may average not more than three inches. But as we pass eastward, 

 beyond the wake of this range, its effects become gradually less ; and long before 

 the Wasatch is reached they have become inconsiderable. Since the Sierra 

 Nevada is the longest, highest and widest of the individualized ranges of the 

 Rocky S|fstem, its local effect upon the humidity of the plains and valleys lying 

 immediately under its lee is greater than that of any other. But the same kind 

 of effect is preceptible in some other ranges. 



The discussion of the causes of local variations in climate might be almost 

 indefinitely extended. Nothing more is designed here than to advert to one 

 general cause of aridity which prevails over the entire region, and which every- 

 where exists, though it is often obscured, sometimes reversed and sometimes 

 reinforced, by local causes. — American Joiirnal of Science. 



