The number of know- 

 facts that are rec( 



ciled by the 



BAINS AND RIVERS. 109 



dence and facts whicli seem to call for a crossing of air at tlie calm 

 belts, as represented by the diagram of the winds, Plate I. It 

 remains for those who deny that there is any such crossing — who 

 also deny that extra-tropical rivers of the northern are fed by rains 

 condensed from vapom-s taken up in the southern hemisphere — to 

 show whence come the hundreds of cubic miles of water which these 

 rivers annually pour into the Atlantic and the Arctic Oceans. In 

 finding the " place " of all this water, it is incumbent upon them 

 to show us the winds which bring it also, and to point out its 

 channels. 



287. '' In the greater number of physical investigations some 

 Spirit in which the hypothcsis is requisite, in the fii'st instance, to aid 

 Ihonw b°e'^con.*'^ the imperfcctiou of om' senses ; and when the phe- 

 <*"^'^^'*^- nomena of nature accord with the assumption, we 

 are justified in believing it to be a general law."* 



288. In this spirit this hypothesis has been made. Without 

 oj^any evidence bearing upon the subject, it would be 



. ir^theory as philosopliical to maintain that there is no cross- 

 caim'^beus"" ^^ ^^^ iug at the calm belts as it would be to hold that 

 there is ; but nature suggests in several instances that there must 

 be a crossing. (1.) In the homogeneousness of the atmosphere 

 (§ 237). The vegetable kingdom takes fi'om it the impurities with 

 which respiration and combustion are continually loading it ; and 

 in the winter, when the vegetable energies of the northern hemi- 

 sphere are asleep, they are in full play in the southern hemisphere. 

 iVnd is it consistent with the spirit of true philosophy to deny the 

 existence, because we may not comprehend the nature, of a contriv- 

 ance in the machinery of the universe which guides the impure 

 air that proceeds from our chimneys and the nostrils of all air- 

 breathing creatures in om- winter over into the other hemisphere 

 for re-elaboration, and which conducts across the calm places and 

 over into this that which has been replenished from the plains and 

 sylvas of the south ? (2.) Most rain, notwithstanding there is 

 most water in the southern hemisphere, falls in this. How can 

 vapour thence come to us except the winds bring it, and how can 

 the wmds fetch it except by crossing the calm places ? (3.) The 

 *' sea-dust " of the southern hemisj)here, as Ehrenberg calls the red 

 fogs of the Atlantic, has its locus on the other side of the equator, 

 but it is found on the wings of the winds in the North Atlantic 



* Mrs. Somcrville. 



