10 THE CYCLONIC DISTRIBUTION OF RAINFALL. 



west, northwest, north or northeast, m the cases studied, but in 

 no instance to the southeast. 



Several features shown in these charts suggest further in- 

 quiries. In the two charts for the semi-arid regions in the south- 

 west and the west, precipitation is most frequent in a crescentic 

 tract on the north side of the central low pressure. To what ex- 

 tent is this characteristic of the cyclones in the west? 



In the two charts representing conditions in the region of the 

 northern part of the central plains, the area of the greatest pre- 

 cipitation has a sigmoid shape. Is this a constant feature for the 

 region, and, if so, what is its cause? 



In the Davenport charts precipitation as well as cloudiness is 

 unexpectedly high in the southernmost tract. Kain and snow are 

 almost as frequent when a low centres three hundred miles north 

 of Lake Superior, as when it lies at Davenport. A study of the 

 conditions which bring about this unexpected precipitation may 

 tlirow some new light on cyclonic conditions in the interior. 



The purpose of this paper is merely to call attention to the 

 method of averaging. It is a truly statistical method which 

 promises a more accurate knowledge of cyclonic conditions than 

 we have had before. Its application will involve a great deal of 

 work. The averages given here pertain only to the conditions for 

 the morning hour. If similar averages could be made for an af- 

 ternoon or for an evening hour, for the same places and periods, 

 it is not unlikely that differences would appear. Again, ii is to be 

 expected that summer and winter cyclones are unlike, and it is be- 

 lieved that there are differences among the cyclones coming along 

 different paths. If this is true, it ought to be shown in such aver- 

 ages as those presented in the above tables. 



A study of all regional, seasonal, and other differences by some 

 such accurate method of averaging can hardly fail to add some 

 important items to our knowledge of cyclonic disturbances. It 

 may be used for any of the elements of the weather. Thus, in the 

 charts which follow, the prevailing wind directions are indicated 



