114 PHYSICAL QEOGllAniX OF THE SJ5A, AND ITH METEOROLOGY. 



these rivers annually pour into the Atlantic and the Arctic 

 Oceans. In finding the "place" of all this water, it is incum- 

 bent upon them to show us the winds ^vhich bring it also, and to 

 point out its channels. 



287. Spirit in wlitcli the sear cli for truth should he conducted. — " In 

 the greater number of physical investigations some hypothesis 

 is requisite, in the first instance, to aid the imperfection of our 

 senses ; and when the phenomena of nature accord with the as- 

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



288. TJie number of known facts that are reconciled by the theory 

 of a crossing at the calm belts. — In this spirit this hypothesis has 

 been made. AVithout any evidence bearing upon the subject, it 

 would be as philosophical to maintain that there is no crossing 

 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 from 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 hemi- 

 sphere. And is it consistent with the spirit of true philosophy 

 to deny the existence, bercause we may not comprehend the 

 nature, of a contrivance in the machiner}^ of the imiverse which 

 guides the impure air that proceeds from our chimneys and the 

 nostrils of all air-breathing creatures in our winter over into the 

 other hemisphere for re-elaboration, and which conducts across 

 the calin places and over into this that which has been re- 

 plenished from the plains and sylvas of the south ? (2.) Most 

 rain, notwithstanding there is most water in the southern hemi- 

 sphere, falls in this. How can vapour thence come to us except 

 the winds bring it, and how can the winds fetch it except 

 by crossing the calm places ? (3.) The " sea-dust " of the 

 southern hemisphere, 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 Ocean. 

 If this be so, it must cross one or more of the calm belts.f 



* Mrs. Somerville. 



t After this had been written, I received from my colleague, Lieut. Andrau, 

 an account of the following httle tell-tale upon this subject : — 



"I found a confirmation of your tlieory in a piece of vegetable substance 

 caught in a small sack (hoisted up above tlie tops) between 22^^-25=' lat. N., and 

 38''-39|° long. W. This piece is of the following dimensions :— 14 millim. long. 



