298 



ENVIRONMENTAL CONDITIONS. 



features. The northwestern portion of the humid province (values 

 below 30) is less extensive, and the Pacific Slope is here depicted as in 

 the semihumid province. The eastern portion of the humid province 

 appears here about as in the case of plate 53, but it does not extend 

 southward farther than Rhode Island, on the Atlantic coast. The arid 

 province (values above 80) is here shown as smaller than in the pre- 

 ceding case. The great eastern lobe of the semiarid province (values 

 between 50 and 80), reaching nearly to the eastern mountains on plate 

 53, is not present on plate 54, but a large area of values above 80 is 

 shown as extending from St. Louis, Missouri, and Louisville, Ken- 

 tucky, to Key West, Florida. 



Evaporation intensities for the three summer months. (Table 15, 

 plate 55.) — Because we shall wish to compare the Russell evapora- 

 tion data with those obtained by ourselves (to be considered below), 

 and since it is impossible to employ the length of the mean frostless 

 season as duration factor in connection with the latter, it is expedient 

 here to study Russell's data for the period of the three summer months, 

 June, July, and August. For a period approximately comparable to 

 this our own data may be studied. 



