THE CENTURY'S PROGRESS IN METEOROLOGY 



urationof the continent into peninsulas ; by the existence 

 of open seas to the north or of radiating continental 

 surfaces to the south ; by mountain ranges to shield 

 from cold winds ; by the infrequency of swamps to be- 

 come congealed ; by the absence of woods in a dry, 

 sandy soil ; and by the serenity of sky in the summer 

 months, and the vicinity of an ocean current bringing 

 water which is of a higher temperature than that of the 

 surrounding sea. 



Conditions opposite to these tend, of course, corre- 

 spondingly to lower the temperature. In a word, Hum- 

 boldt says the climatic distribution of heat depends on 

 the relative distribution of land and sea, and on the 

 " hypsometrical configuration of the continents " ; and 

 he urges that " great meteorological phenomena cannot 

 be comprehended when considered independently of 

 geognostic relations " a truth which, like most other 

 general principles, seems simple enough once it is 

 pointed out. 



With that broad sweep of imagination which charac- 

 terized him, Hum bold t speaks of the atmosphere as the 

 "aerial ocean, in the lower strata and on the shoals of 

 which we live," and he studies the atmospheric phe- 

 nomena always in relation to those of that other ocean 

 of water. In each of these oceans there are vast per- 

 manent currents, flowing always in determinate direc- 

 tions, which enormously modify the climatic conditions 

 of every zone. The ocean of air is a vast maelstrom, 

 boiling up always under the influence of the sun's heat 

 at the equator, and flowing as an upper current towards 

 either pole, while an under current from the poles, which 

 becomes the trade- winds, flows towards the equator to 



supply its place. 



M 177 



