Climate of the Canadian West. ou 
and at the summit of the Rockies the atmosphere is almost 
perfectly thin, dry and cold. The eastern slope of the 
Rockies is sparsely supplied with trees, and those of small 
size, while the rivers are scanty, except those fed by the 
glaciers and great snow banks conserved upon the cold 
central heights, and slowly doled out to keep the streams 
running. No great freshets occur, as happens upon the 
Pacific slope. 
Yet the eastern foothills of the Rockies have a milder 
climate, and earlier spring and less snow than the western 
base of the range. Why? Owing to the Chinook winds. 
But what are the Chinook winds? Currents of warm air— 
broad sheets—cataracts—of warm air falling down in mid- 
winter from the top of the Rockies. But why, if the air 
on the crest, where the wide spaces of snow lie, is deadly 
edld, should the breezes decending from those snow-fields 
be comfortably warm in winter? Simply because they do 
descend. 
Here is the reversal of the previous condition. The air 
ascending the western side and at the top of the Rockies is 
cold because it is losing its moisture and becoming rarified ; 
the air descending the eastern slope becomes condensed, 
picks up moisture with every part of its descent, and cor. 
respondingly develops, or gives up, the latent heat which 
invariably accompanies condensation, The Chinook, then, 
is a warm dry wind, manufactured on the spot by the 
condensation of the mountain air as it sweeps down, increas- 
ing in density, absorbing moisture, and yielding up its 
latent heat. In summer the same breeze seems cool in 
comparison with the fierce radiation of the baked plains ; 
but it is equally a Chinook. 
This wind is marvelous in its effect. To it is due the 
pleasing dryness of even the deepest gorges and nooks in 
the rocks in summer, while in winter it clears the plains for 
hundreds of miles away from the mountains of nearly all 
the snow—always scanty in amount—with amazing celerity. 
A northern gale will blow for two or three days, forcing the 
mercury below zero, and bringing all the wide plains under 
