90 
NATURE FOR ITS OWN SAKE 
Causes of 
clouds and 
rain. 
Eastern 
storms, how 
produced, 
and it would inevitably fall to earth as a 
shower. 
It is now generally held, I believe, that the 
cause of clouds and rain is largely, if not en- 
tirely, the cooling of air by expansion as it as- 
cends; and that intermingled cold and warm 
air, and the chilling of air by cold bodies such 
as mountain-tops, have little or no effect. Cer- 
tainly the expansion of air is the final but not 
always the most immediate cause. The chill- 
ing produced by warm air driven against cold 
air and its result may be frequently witnessed 
in the winter season along the Atlantic coast of 
North America. When the wind shifts to the 
east we are all quite sure that thirty-six hours 
at least will bring rain, and usually it is not so 
long before the clouds begin to drift inland 
from the sea. It is sometimes thought that 
there is a storm on the ocean, and that it has 
been travelling landward for hundreds of miles. 
Occasionally that is the case, but more often 
the clouds and rain are formed along our own 
coast, and in this way : The sea is much warmer 
than the land, especially in the Gulf Stream 
region. Vast bodies of moist air overhanging 
it are driven in upon the land by the eastern 
winds. This land is ice-locked and very cold. 
