CLIMATOLOGY. 315 



idea of their climatic relations, as influential on agriculture 

 and other industrial pursuits, and on the comfort and well- 

 being of man. 



In enumerating the causes which exercise a disturbing 

 influence on the form of the isothermal lines, I have distin- 

 guished between those which raise and those which depress 

 the temperature. To the first belong, the vicinity of a 

 western coast in the temperate zone; a divided or inter- 

 sected configuration of the land, with projecting peninsulas, 

 and deep re-entering bays and inland seas ; aspect, or the 

 position *of the land relatively to a sea free from ice ex- 

 tending within the polar circle, or to a considerable mass 

 of continental land situated beneath the equator, or at 

 least within the torrid zone; prevalence of southerly and 

 westerly winds on the western side of a continent, in the 

 temperate zone of the northern hemisphere ; chains of 

 mountains acting as screens or protecting walls against 

 winds from colder regions; infrequency of swamps or 

 marshes, which retain the ice in spring and early summer; 

 absence of woods on a dry sandy soil ; constant serenity 

 of sky during the summer months ; and lastly, the vicinity 

 of an oceanic current, bringing water of a higher tempera- 

 ture than that of the surrounding sea. 



Among the cooling causes which modify the mean 

 annual temperature, I consider elevation above the sea level, 

 especially when not forming an extensive table land; the 

 vicinity of an eastern coast in the higher and middle lati- 

 tudes ; the compact and massive form of a continent, having 

 a coast line little varied by indentations ; an extension of 

 the land in the direction of the pole far into the frozen 

 regions (there being no intervening sea free from ice during 



