90 Canadian Record of Science. 
the coolness of the air increases in pace with its rarification. 
Professor McCleod, in the second lecture of this course, 
made this plain by his diagrams, showing how an increase 
of altitude above the sea is equal to an increase of latitude 
away from the Equator, until, on the tops of very lofty 
mountains truly polar weather exists. The summits of the 
eastern Rockies are not much higher, however, than the 
crests of the Gold and Selkirk ranges; and they are colder 
than their more western compeers, not because they are 
higher, but because they are more inland, and hence receive 
air already dry, rarified and well cooled. 
It is this characteristic of the atmosphere of the eastern 
side of the Rockies—-in the neighborhood of Banff Springs, 
for instance—which gives it such a sanitary value, particu- 
larly in diseases of the lungs and throat, 
Now let us make a hasty review: The winds of British 
Columbia are, broadly speaking, from the west. They are 
warm from the ocean, and loaded with moisture. Condens- 
ing into fog at the coast, they give a uniform, English-like, 
muggy climate along the Pacific coast. Further condensed, 
they are less foggy, but produce a more cloudy sky and 
heavier rainfall on the coast mountains. Raised to the 
elevation of the crest of the Cascades or Coast range, they 
take a flying leap across the interior basin, discharging 
little rain on the Thompson valley,—leaving it subject to 
extreme cold in winter, excessive heat in summer, and 
drought all the time. Condensed again by the Gold Range, 
the moist winds give those mountains rain and heat almost 
equal to that of the Coast Range. Condensed still further, 
by the Selkirks, there is a copious rainfall and snowfall upon 
these mountains, and a further giving up of warmth, which 
greatly tempers the climate; but by the time the Selkirks 
are past, the winds have lost nearly all their moisture and 
warmth, and have been rarified by being forced to an aver- 
age height of seven or eight thousand feet. Hence, when 
they pass to the Rockies they are dry and cool in summer— 
dry and very cold in winter. What little humidity and 
warmth they may retain is almost lost on the western slope, 
