138 



THE ANDES OF SOUTHERN PERU 



Scale of 



Cloudiness 



1889 

 A S N D J 



1890 

 FMAMJ J A S 



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SR 







1 1 



SUMMER 









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11 



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Gulf of Guayaquil. Such was the case in the phenomenally rainy 



year of 1891. The connection is obscure, but undoubtedly exists. 



The effects of the heavy rains are amazing and appear the 



more so because of the extreme aridity of the country east of 



them. During the winter 

 the desert traveler finds the 

 air temperature rising to 

 uncomfortable levels. Vege- 

 tation of any sort may be 

 completely lacking. As he 

 approaches the leeward 

 slope of the Coast Range, a 

 cloud mantle full of refresh- 

 ing promise may be seen 

 just peeping over the crest 

 (Fig. 91). Long, slender 

 cloud filaments project east- 

 ward over the margin of the 

 desert. They are traveling 

 rapidly but they never ad- 

 vance far over the hot 

 wastes, for their eastern 

 margins are constantly un- 

 dergoing evaporation. At times the top of the cloud bank rises 

 well above the crest of the Coast Range, and it seems to the man 

 from the temperate zone as if a great thunderstorm were rising in 

 the west. But for all their menace of wind and rain the clouds 

 never get beyond the desert outposts. In the summer season the 

 aspect changes, the heavy yellow sky of the desert displaces the 

 murk of the coastal mountains and the bordering sea. 



It is an age-old strife renewed every year and limited to a nar- 

 row field of action, wonderfully easy to observe. We saw it in its 

 most striking form at the end of the winter season in October, 

 1911, and for more than a day watched the dark clouds rise omi- 

 nously only to melt into nothing where the desert holds sway. At 

 night we camped beside a scum-coated pool of alkali water no 



Fig. 90 — Cloudiness at Chosica, July, 1889, 

 to September, 1890. Chosica, a station on 

 the Oroya railroad east of Lima, is situated 

 on the border region between the desert zone 

 of the coast and the mountain zone of yearly 

 rains. The minimum cloudiness recorded about 

 11 a. m. is shown by a broken line; the maxi- 

 mum cloudiness, about 7 p. m., by a dotted 

 line, and the mean for the 24 hours by a heavy 

 solid line. The curves are drawn from data 

 in Peruvian Meteorology, 1889-1890, Annals 

 of the Astronomical Observatory of Harvard 

 College, Vol. 39, Pt. 1, Cambridge, Mass., 1899. 



