640 



SCIENCE 



[N. S. Vol. XLV. No. 1173 



dates for planting. Thus, "wlien the silver 

 maples begin to put forth their leaves and the 

 catkins appear on the willows and poplars, na- 

 ture is indicating that the season is right for 

 the planting of such vegetables as lettuce, mus- 

 tard, onion seeds and onion sets, parsley, the 

 round seeded peas, early Irish potatoes, rad- 

 ishes, spinach and turnips." * Ten days later 

 beets, carrots, kohl-rabi and a second sowing 

 of peas can be made. 



CLIMATOLOGY OF THE PERUVIAN ANDES 



Dr. Isaiah Bowman has devoted one sixth of 

 his recent book, " The Andes of Southern 

 Peru" (336 pp.. New York, 1916) to a weU-il- 

 lustrated discussion of the perplexing diversi- 

 ties of Peruvian climates. There are four cli- 

 matic belts: (1) the wet, eastern lowlands, cov- 

 ered with heavy tropical forest; (2) the wet, 

 windward mountain slopes, with mountain for- 

 est extending up to the cold timber line at 10,- 

 500 feet, and in protected valleys down to a 

 dry timber line at 3,000 feet; (3) semi-arid 

 mountains, plateaus and basins, covered with 

 grass, moss and alpine plants; (4) the arid 

 coastal zone of irrigated valleys, barren except 

 along valley floors and on the seaward slopes 

 of low coast ranges. 



On the wet, windward mountain slopes the 

 belt of heaviest rainfall is between 4,000 and 

 10,000 feet. Summer is rainiest, for the force 

 of the trade wind by day is greatly increased 

 by virtue of the greater contrast between the 

 highland and lowland temperatures. In the 

 deep, shut-in valleys of the eastern mountains, 

 conditions of marked aridity are found. The 

 local climates of the semi-arid mountains, 

 plateaus and basins depend on altitude, and 

 thus differ primarily in temperature and winds. 

 The chapter on " Meteorological Records from 

 the Peruvian Andes," adds the daily touch to 

 the preceding general discussion of climate. 

 Extensive diagrams, including daily tempera- 

 ture maxima, minima, variability, and daily 

 rainfall show a tropical steadiness, but, withal, 

 sudden weather changes and considerable dif- 

 ferences between corresponding seasons of dif- 



4 TJ. S. Dept. Agric. "Weekly News Letter, Mar. 

 24, 1915. 



ferent years. The diagrams taken from ther- 

 mograph tracings show vividly the effect on 

 the temperature of changes of wind, the pass- 

 ing of clouds or the inception of storms. The 

 Tale Peruvian Expeditions with the National 

 Geographic Society still maintain some mete- 

 orological stations in Peru. 



The climates of the coast are the most diffi- 

 cult to explain. Widely accepted are the gen- 

 eral explanations of the coastal desert of 

 northern Chile and of Peru: that the deserts 

 are there because the normal trade winds blow f 



over the mountains and on descending are 

 warming, drying winds; and that the cold 

 coastal water intensifies the dryness because ■ 

 any winds thence have little tendency to yield 

 rainfall over a warm land. This cold water is 

 an adjunct of the prevailing offshore " trades," 

 for the warm surface water blown out to sea is 

 replaced by cold abysmal water. In southern 

 Peru, Bowman distinguishes five zones from 

 coast to mountains: (a) zone of coastal ter- 

 races, rain once in many years; (h) zone of 

 fog-covered mountains, rain at intervals of 

 5-10 years; (c) zone of desert plains, rain at 

 intervals of many years; (d) zone of steep val- 

 leys, yearly rains; (e) zone of lofty mountains 

 and plateaus, frequent rains in summer 

 months. 



The sea-breeze is the most important mete- 

 orological feature of the coast. By day the 

 heating of the land on a slope tends to make 

 an up-hill wind; the heating of the land next 

 to cold water tends to make a breeze on-shore. 

 Combined, these two factors make a wind 

 which blows so strongly that shipping opera- 

 tions in the afternoon are hindered or ren- 

 dered impossible. Its coming at or before noon 

 is uncomfortably boistrous and dusty. On the 

 coast the highest temperature occurs just be- 

 fore the sea-breeze arrives. The coast range, 

 where present, makes this wind rise abruptly 

 several thousand feet, which generally causes 

 fog at 2,000 to 4,000 feet elevation, and in win- 

 ter some rainfall. Beyond the coast range, 

 however, the air is warmed, and mixed rapidly 

 by convection with the high dry air so that no 

 more condensation occurs imtil it approaches 

 the western Cordillera. There the topograph- 



