15G NOTES OX MANITOBA. 



sideration, wliy 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 : 



1st. 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 westwai-d of the tract ruftning 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 argiiment is needed, to show that the causa of the 

 divergence of the eastern thermometric current to tlie 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 Noi'thern 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 efiect of which is that the isothermals 

 pass away from their northern altitude and sink southward next, 

 Avhen 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 cui-rents from the north and from the west 

 follow them up, particulaily 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 otlier, bring the minimum line of cold 

 so far to the south. Were the American Desert an inland sea, the 

 sumniei's of our plains would lose their exceptional character, and 

 our winters wjuld be like those of Eastern Europe. 



