EASTING OP THE TRADE-WINDS, ETC. 165 



tiTie that K S cany the vapour which, by condensation, is to water 

 with showers the extra-tropical regions of the northern hemi- 

 gphere, Nature, we may be sure, has provided a guide for con- 

 ductino- S T across this belt of calms, and for sending it on in the 

 rio-ht way. Here it was, then, at this crossing of the winds, that 

 I thouo-ht I first saw the footprints of an agent whose character I 

 could not comprehend. Can it be the magnetism that resides in 

 the oxygen of the air ? Heat and cold, the early and the latter 

 rain, clouds and sunshine, are not, we may rely upon it, distributed 

 over the earth, by chance ; they are distributed in obedience to 

 laws that are as certain and as sure in their operations as the 

 seasons in their rounds. If it depended upon chance whether the 

 dry air should come out on this side or on that of this calm belt, or 

 whether the moist air should return or not whence it came — if such 

 were the case in nature, we perceive that, so far from any regularity 

 as to seasons, we should have, or might have, years of drought the 

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

 tive ; but, so far from this, we find for each place a mean annual 

 proportion of both, and that so regulated withal, that year after 

 year the quantity is preserved with remarkable regularity. 

 Having thus shown 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 shown that there is reason for supposing that the air of 

 each current, after descending, continues on in the direction 

 towards which it was travelling before it descended, we may go 

 farther, and, by a similar train of circumstantial evidence, 

 afforded by these researches and other sources of information, 

 show that the air, kept in motion on the surface by the two 

 systems of trade-winds, when it arrives at the belt of equatorial 

 calms and ascends, continues on thence, each current towards 

 the pole which it was approaching while on the surface. In a 

 problem like this, demonstration in the positive way is difficult, 

 if not impossible. We must rely for our proof upon philo- 

 sc phical deduction, guided by the lights of reason ; and in all 

 cases in which positive proof cannot be adduced, it is permitted 

 to bring in circumstantial ' evidence ; and the circumstantial 

 evidence afforded by my investigations goes to show that the 

 winds represented by Q, § 215, do become those represented 

 by K S T U V A, and A B C D E F respectively. In the first 

 place, Q represents the south-east trade-winds—/, e., all the 



