NIND. 
cessive current is formed, to which our coast and inland 
mountains give a north-east direction *” 
Currents of air from the poles naturally, as has been 
observed, assume a north-east direction as they advance 
southwards ; because their diurnal motion becomes less 
than that of the earth. Various circumstances, how 
ever, may change this direction, and cause them to be 
come north, or even north-west, winds. The south 
west winds themselves may often prove sufficient for 
this ; and violent rains, or great heat, by lessening or 
rarefying the atmosphere in any country, will produce 
the same effect in countries to the westwards when 
north winds happen to be blowing. 
In North America, the north-west winds become gra 
dually more frequent as we advance northwards. The 
east coast of this continent, where the observations 
were made from which this conclusion was drawn, is 
alone cultivated; the rest of the country is covered with 
wood. Now cultivated countries are well known to be 
warmer than those which are uncultivated; the earth 
in the latter is shaded from the sun, and never heated 
by his rays. The air, therefore, in the interior parts 
of America, must be constantly colder than near the 
east coast. This difference will hardly be perceptible in 
the southern parts, because there the influence of the 
sun is very powerful; but it will become gradually 
greater as we advance northwards, because the influence 
of the sun diminishes, and the continent becomes 
broader. Hence north-west winds ought to become 
more frequent upon the east coast as we advance north 
wards ; and they will probabty cease to blow so often 
* Franklin's Philosopbical Letters, p. 389. 
Z 3 
357. 
Chep. I.