CLIMATOLOGY OF THE PERUVIAN ANDES 



133 



shows that 95 per cent of the winds with strength over 10 miles per 

 hour blew from a southerly direction. Yet during this season the 

 coast is generally clearest of fog and cloud. The explanation ap- 

 pears to lie in the exceedingly delicate nature of the adjustments 

 between the various rain-making forces. The relative humidity 

 of the air from the sea is al- 



June, July- 



Dec, Jan. 



9 a.m. 



3 p.m. 



9 p.m. 



ways high, but on the im- 

 mediate coast is slightly less 

 so in summer than in win- 

 ter. Thus in Mollendo the 

 relative humidity during the 

 winter of 1895 was 81 per 

 cent; during the summer 78 

 per cent. Moreover, the 

 temperature of the Coast 

 Range is considerably higher 

 in summer than in winter, 

 and there is a tendency to 

 reevaporation of any mois- 

 ture that may be blown 

 against it. The immediate 

 shore, indeed, may still be 

 cloudy as is the case at Cal- 

 lao, which actually has its 

 cloudiest season in the sum- 

 mer, but the hills are com- 

 paratively clear. In conse- 

 quence the sea-air passes 

 over into the desert, where 

 the relative increase in tem- 

 perature has not been so 

 great (compare Mollendo and La Joya in the curve for mean 

 monthly temperature), with much higher vapor content than in 

 winter. The relative humidity for the winter season at La Joya, 

 1895, was 42.5 per cent; for the summer season 57 per cent. The 

 influence of the great barrier of the Maritime Cordillera, aided 



—.Completely 

 iz4a Overcast 



Scale o£ Cloudiness 



C3 Clear EM 0-2.5 E23 2.5-7.5 ^9.5-10 



Fig. S4 — Cloudiness at Callao. Figures 

 are drawn from data in the Boletin de la 

 Sociedad Geografica de Lima, Vols. 7 and 8, 

 1898-1900. They represent the conditions at 

 three observation hours during the summers 

 (Dee., Jan.) of 1897-1898, 1898-1899, 1899- 

 1900 and the winters (June, July) of 1898 and 

 1899. 



