40 Dr. Forry on the Climate of the United States, S^c. 



tion ; while some, even now, as for instance Lyell, as already 

 quoted, make Europe the exception to the general rule. But 

 when these facts came to be generalized, it was discovered that 

 the eastern coasts of both continents have a lower annual tem- 

 perature and more contrasted seasons than the western in corre- 

 sponding latitudes. These results find a satisfactory explanation 

 in physical causes, thus demonstrating the harmony of the laws 

 of climate throughout the globe. 



Did space allow, it would be easy to show that the rationale 

 of all these laws finds a ready explanation in the phenomena of 

 the polar and equatorial currents, in connection with certain local 

 causes. Suffice it to refer to a single explanation. The winds 

 without the tropics have a prevailing direction from the west, — • 

 a fact which affords a solution of the problem that in extra-trop- 

 ical latitudes, countries lying to the eastward of seas or other 

 great bodies of water, have milder climates than those situated 

 on the eastern portions of a continent. That this westerly breeze 

 prevails with considerable regularity, is apparent from the follow- 

 ing observations made by John Hamilton, during twenty six 

 voyages between Philadelphia and Liverpool from 1798 to 1817, 

 showing that the winds were more than half the time from the 

 west. Thus, out of 2029 days, the wind prevailed 



From northward, .... 208 days. 

 " southward, . . . . 167 " 

 " eastward, . . . . 361 " 

 " westward, .... 1101 " 

 Variable, 192 " 



2029 



We thus perceive at once the principal cause of the rise of the 

 isothermal line on the western coast of continents in extra-trop- 

 ical latitudes ; for there is thus swept from the ocean, which 

 never sinks below the freezing point, a humid atmosphere, which, 

 in its passage over the land, has a constant tendency to establish 

 an equilibrium of temperature, and as its vapor is gradually con- 

 densed, it also evolves its latent heat. As large bodies of water 

 never become so cold in winter or so warm in summer as the 

 earth, the winds that sweep from them have a constant tendency 

 to maintain an equilibrium of temperature. Land winds, on the 

 contrary, must necessarily bear with them the greater or less de- 



