248 



THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. 



departures from the mean temperature at Bombay were due to the same cause as those at 

 Arequipa and the other stations, but the direct effects of this appear to produce only minor 

 maxima, such as those of 1905 and 1907, while the greatest effects are produced after a delay 

 of a year or so, during which the excess of temperature accumulated farther south is perhaps 

 brought north by ocean currents driven by the monsoons. 



The supposition of a delay of this sort is strengthened by the curves presented in figure 

 84. Here Arctowski has compared the departures from mean temperature at Arequipa with 

 those of a series of stations from Key West along the Atlantic coast to Eastport. Here, just 

 as in the other case, agreement gives place to disagreement when a pronounced disturbing 

 factor is introduced. The curves for Key West, Tampa, and Savannah agree quite closely 

 with that of Arequipa from 1900 to 1905, when the maxima come in winter, but there- 

 after they disagree markedly when the Ai-equipa maximum comes in summer. In this 

 case the factor is not the monsoons, but may be the concentration of warm equatorial 



1900 



1910 



Fig. S3.— Monthly Departures of Temperature in North and South Equatorial 

 liegions, Showing Disagreement, after .\rctowski. 



waters to form the Gulf Stream. North of the West Indies conditions once more change, 

 and New York agrees with i\j-equipa, but with a delay of a few months. This may mean 

 one of two tilings: either the temperature of New York responds directly to the same 

 stimulus as Ai-equipa, perhaps because of its dependence upon a great continent easily 

 warmed, or else (which seems much less hkely) it responds indirectly and wdth a delay 

 approximately equal to the average lapse of time from one Arequipa minimum to the next. 

 This might happen if the variations of the New York temperature were largely dependent 

 on the Gulf Stream, but as a matter of fact they depend more largely upon great interior 

 regions whence come our westerly winds. 



The sun's radiation is distributed equally to all parts of the earth, but the inclination 

 of the axis, the variations of the seasons, the distribution of land and sea, the presence of 

 clouds, the movements of winds and ocean currents, and a host of other accidental cir- 

 cumstances cause it to be concentrated now in one place and now in another. In equatorial 

 regions and in the North Atlantic Ocean there is a permanent concentration, so that the 

 temperature is relatively high. Over the continents a temporary concentration occurs in 

 summer. If the sun's total gift of heat to the earth is thus kregularly distributed, the 

 effect of any variations from the average must be distributed in the same irregular fashion, 

 being concentrated at the equator or over the North Atlantic at all times, over the con- 

 tinents in summer, and in other places according to local cuxumstances. A result of this 

 concentration is perhaps seen in the middle of 1901. At Arequipa (for some reason which 



