202 CLIMATE AND CAUSES 



to the agriculturist, which, I believe, are unsurpassed in any other 

 part of the world. 



"Returning to the course taken by the east and west currents, 

 before their union at the Hand Hills, it is a matter for considera- 

 tion why that from the east departs from the natural law which 

 would give to it an eastward, in place of a western bend, while 

 the western current follows the natural law and bends to the 

 eastward. 



"The answer to this question is the key to almost every 

 climatological peculiarity of the North West. 



"The data which we have for the investigation of the ques- 

 tion: "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 the land or 

 water adjoining. 



2nd. Recorded observations which show that currents of 

 air are constantly on the move to 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." 



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 the Western 

 Indies, and result in the south west "Monsoon," and, further, by 

 the northeastern 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 this is that the isothermals pass away from their 

 northern latitude 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, 



