Canadian Ar/n'cuUure. 
237 
Macoun. The conditions which determine the climate of the 
vast continental region occupied by the prairie may be most 
conveniently studied as the factors of a physiographical problem 
of national importance. The normal seasons comprise a long, 
severe, but dry winter, a hot summer with abundant rain, a 
short pleasant autumn or " fall," and a still briefer spring, 
which is usually dry and sunny. The opening of spring, as 
marked by the first appearance of spring flowers, is about the 
middle of April, the period being practically the same over the 
entire area. The diurnal temperature rapidly rises, and summer 
heat prevails till the middle of August, about which time a great 
and permanent fall in temperature takes place, and autumn sets 
in ; the closing days of this latter season are often very beautiful, 
and they form the period known as the Indian summer. Winter 
begins within the first fortnight of November, the navigation of 
the Red River being closed simultaneously, though the Peace 
River, much farther north, usually closes later. Unfortunately, 
our English conceptions of the climate of the Canadian prairie 
are based almost exclusively on the readings of the thermometer. 
We hear, for example, of a temperature of 20° below zero on a 
winter day in Manitoba, and shudder at the bare thought of 
such extreme severity, as we try to imagine what suffering such 
a temperature would bring with it in England. But this is 
where the error creeps in, for the bodily sensations accompany- 
ing a temperature of, say, — 20° in England, and those associated 
with the same temperature on the Canadian prairie would be 
quite different. In fact, the thermometer alone is an insufficient 
guide ; besides knowing the temperature of the air, it is also 
necessary to know the amount of moisture it contains, before 
arriving at a conclusion as to the agreeableness or otherwise of 
the atmospheric environment. Dry air is a bad conductor of 
heat ; moist air is a better conductor, the conducting medium 
really being the water vapour or water dust which confers the 
moistness, so that, below the point of saturation, the more 
moisture the atmosphere contains the more freely will it conduct 
away heat from the surfaces of the animal body.* On the other 
hand, the drier the air is, the more completely does it act as an 
insulator, enveloping the animal body in a medium which 
conserves the animal warmth in so far as it offers no facility for 
the escape of the latter by conduction. These simple physical 
facts supply the reason that the winter temperatures of the 
* " Varying amounts of moisture in the air materially affect the health and 
comfort of man. . . . Moist air is a better conductor of heat than dry air, -which 
accounts for much of the discomfort felt in winter when a thaw takes place as 
compared with the feeling of elasticity when the air is dry. In cold weather, 
therefore, moist air cools down the skin and lungs more rapidly than dry air, and 
colds consequently result." — ' On some relations of Meteorological Phenomena to 
Health.' By John W. Tripe, M.D., F.E.Jlet. Soc. 
