160 



SCIENCE 



[N. S. Vol. XLIX. No. 1259 



over cold areas, such as Greenland, Antarctica, 

 etc., and the latter over regions that are warm 

 in comparison with neighboring areas, such as 

 the water southeast of Greenland, the Gulf 

 of Alaska (in the winter), etc. All such cases 

 are readily explained on the principle of 

 thermal convection, and therefore offer noth- 



thermal origin. Presumably, therefore, their 

 circulations are largely driven and their tem- 

 peratures in part mechanically determined. 



As every one knows, the temperature con- 

 trast between the regions of low and high 

 latitudes, respectively, leads to an interzonal 

 circulation of the atmosphere. And because 

 of the rotation of the earth this circulation 



-60° -55" -50" -45° -40' -35' -30° -25' -20° -15° -10" -5* 0' 5* 10° 15* 

 TEMPERATURE 



Fig. 2. Eelation of summer temperatures to barometric pressure. 



The migratory storms, however, at least 

 those of middle latitudes, are quite different. 

 The relation of their temperatures to each 

 other, level for level up to the stratosphere, 

 is just the reverse of that which it would have 

 to be if their circulations were of immediate 



becomes, throiTgh a portion of its course, the 

 prevailing winds from the west, that up to 

 near the base of the stratosphere average 

 stronger, and are more nearly constant in 

 direction, with increase of altitude. Now, 

 whatever the origin of the migratory anticy- 



