Facts in Meteorology. 133 
Of Climate, as connected with the Atmospheric and Oceanic Currents. 
The term climate, expresses that particular combination of tem- 
perature and moisture, which exists in the atmosphere of any greater 
or less extent of country. 
The temperature of the sea has an effect upon the winds which 
pass over it, and this temperature being more equable than that of | 
the land, tends to equalize the temperature of an island or a mari- 
time country. The temperature of the ocean, contiguous to any 
country, also depends much upon the position of that country in re- 
lation to the great oceanic currents. 
It is the character of the prevailing winds which chiefly, and more 
‘immediately, affects the climate of any country situate without the 
tropics. ‘The currents of the atmosphere, like those of the ocean, | 
form a system of continued circuits, by which the accumulated 
warmth of one region is often conveyed to another, and by this 
means important modifications of climate are produced 
Mountains also affect climate in more ways than one. By causing 
the condensation of aqueous vapor they occasion copious rains. They 
also afford shelter:from winds ; and by their position modify or con- 
trol the currents of the lower atmosphere, and sometimes occasion 
great diversities in the climate of countries and places near to each 
her. ; 
The climate of the United States and Canada strongly illustrates 
the influence of these causes. The tropical current or trade wind, 
being deflected by the Mexican elevations, enters the great basin of 
the Mississippi and sweeps freely over the extensive country lying 
east of the Rocky mountains. Here, by change of latitude, the 
diurnal motion of the surface becomes less than that of the super- ° 
incumbent fluid, which therefore necessarily assumes the form of 
westerly winds, and passes back to the Atlantic, to be in due time 
again merged in the north-easterly trades. When this tropical cur- 
rent keeps sole possession of the surface, which it often for 
days together, extraordinary heat prevails, extending frequently 
through the entire basin of the St. Lawrence, and sometimes rais- 
ing the thermometer on the borders of that river, at Montreal, to 
98 degrees of Fahrenheit. But in winter, when the locality of this 
great circuit is changed to a more southern region, and when its cur- 
rent is entirely displaced from the surface of the great interior pla- 
teau by the cold winds of the interior, which’ come down from the 
