38 AVERAGE TEMPERATURE AND FALL OF RAIN. 



The United States may be divided with reference to the 

 fall of rain into three regions, namely : the region of peri- 

 odical rains, the region of frequent rains, and the region 

 of scanty rains. 



The region of periodical rains comprises the western 

 division of the Pacific slope. 



In that portion of this division south of the 40th parallel 

 of latitude, scarcely any rain falls in summer, and very 

 little in autumn. The quantity in winter somewhat ex- 

 ceeds that- which falls during the spring. 



A much greater quantity of rain falls upon that part of 

 the division north of lat. 40 than south of it ; but, as in 

 the southern division, the largest amount belongs to the 

 winter and spring. 



The region of frequent rains extends from the Atlantic 

 coast westward to about the 100th meridian of longitude. 

 This region, considered as a whole, is exceedingly well 

 watered, the rain being quite equally distributed through 

 the different seasons. 



From an examination of the table, it will appear that 

 along the Atlantic slope, as far south as Washington, very 

 nearly the same annual quantity of rain falls ; and that it 

 is very equally distributed throughout the year. In the 

 Gulf States, and along the Atlantic slope south of Wash- 

 ington, the annual amount of rain is much greater than in 

 the other sections, and the summer rains are much more 

 abundant than those of the winter. In the interior the 



