156 NOTES ON MANITOBA. 
sideration, why that from the east should depart, not only, from the 
natural law which would give to it an eastward, in place of a west- 
ward, bend as it rises northward from the Gulf of Mexico, but also 
from that of the western current which follows the natural law and 
bends to the eastward. 
The answer to this question is the key and the solution of almost 
every climatological peculiarity of the North-West. 
The data which we have for the investigation of the question : 
Why does the eastern current of heat proceeding north-westward 
from the Gulf of Mexico bend to the west? are: 
Ist. Recorded observations which show that land of a desert 
character is heated to a greater degree than that without its bounds. 
2nd. Recorded observations which show that currents of air are 
constantly on the move to the spots where the land is most heated. 
3rd. The fact that to the westward of the tract running northward 
from the Gulf of Mexico lies the “Great American Desert,” which, 
from the preceding statements, must exercise an influence on the air 
around it. 
To my mind, no argument is needed to show that the cause of the 
divergence of the eastern thermometric current to the westward is 
solely due to the position and effect produced by the American 
Desert. A confirmation of this inference is offered in the eastern 
hemisphere where the south-east trade winds are drawn out of their 
course by the heated atmosphere of Western Indies, and result in the 
South-West Monsoon, and further by the north-eastern trend of the 
isothermals in Northern Asia. In the transition from summer to 
winter we find the Desert losing its temperature (terrestrial and 
atmospheric), and consequent attractive influence on air currents 
warmer than its own, the first effect of which is that the isothermals 
pass away from their northern altitude and sink southward next, 
when freed from the desert influences, they no longer trend to the 
westward, but to the eastward. On the withdrawal of the southern 
warm currents, other currents from the north and from the west 
follow them up, particularly on the east side of the Rockies, and 
establish the prevailing north-west winter winds, which, being 
affected by the temperature of the Arctic Regions on the one hand, 
and by the Mountains on the other, bring the minimum line of cold 
so far to the south. Were the American Desert an inland sea, the 
summers of our plains would lose their exceptional character, and 
our winters would be like those of Eastern Europe. 
