276 Lieut. Maury on the Probable Relation bettveen^ 



the most excessive, and then again seasons of rains the most 

 destructive ; but so far from this we find for each place a 

 mean annual proportion of both, that year after year is pre- 

 served with remarkable regularity. 



Therefore, seeing reasons why s' and 8" should cross each 

 other in the calms of Cancer, and seeing no reasons why they 

 should not, I was led to the inference, that here probably is 

 a node in the circulation of the atmosphere, where the wind 

 from the north meets the wind from the south, and that each 

 after a pause, continues on its course and returns again to 

 complete his circuit. The fact, it appeared to me, was pro- 

 bable, but the cause a mystery ; that is, did this crossing of 

 currents not take place, here would be a barrier in the atmo- 

 sphere : and we, the inhabitants of the extra tropical regions 

 of the north, would have an atmosphere, between the calms 

 of Cancer and the pole, always to breathe. 



Having thus shewn that there is no reason for supposing 

 that the upper currents of air when they meet over the calms 

 of Cancer and Capricorn, are turned back to the equator ; 

 but having shewn that there is reason for supposing that the 

 air of each current after descending, continues on in the 

 direction towards which it was travelling ; we may go farther, 

 and by a similar train of circumstantial evidence, afforded by 

 the charts and other sources of information, show that the 

 air moved on the surface by the two systems of trade winds, 

 when arrived at the belt of equatorial calms, and having as- 

 cended, continues on thence, each current towards the pole 

 which it was approaching w^hile on the surface. 



There is no reason for supposing that the atmosphere does 

 not pass freely from one hemisphere to another ; on the 

 contrary, many reasons for supposing that it does, present 

 themselves. 



If it did not the proportion of land and water, and conse- 

 quently of plants and warm blooded animals being so different 

 in the two hemispheres, we might imagine that the consti- 

 tuents of the atmosphere in them would, in the course of ages, 

 probably become diiferent, and that consequently, in such a 

 case, man could not safely pass from one hemisphere to the 

 other. 



