108 THE PHYSICAL GEOGRAPHY OF THE SEA. 



Spirit in wiiicii the liypothcsis is requisite, in the first instance, to aid 

 shouM b?^condu"ct- ^^e imperfection of our 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 

 The number of known auv cvidcnce bearing upon the subject, it would be 

 ciied by the theoiy as philosopliical to maintain that there is no cross- 



of a crossing at the . , ^ ^ . ttt iiti 



calm belts. lud: at thc cami 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 hemisphere. 

 And 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 our 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 

 vapor 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 Ehrcnberg calls the red 

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

 but it is found in the winds of the North Atlantic Ocean. If this 

 be so, it must cross one or more of the calm belts.f (4.) Parallel 



* Mrs. Somerville. 



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

 account of the following little tell-tale upon this subject : 



"I found a confirmation of your theory in apiece of vegetable substance caught in 

 a small sack (hoisted up above the tops) between 22°-25° lat. N., and 38°-39^° long. 

 W. This piece is of thc following dimensions: ]4 millim. long, 1 to H mm. large, 

 -1- mm. thick, and weighing 11- milligrams. Our famous microscopist and naturalist, 

 ]'rofessor P. Harting, at Utrecht, told me, after aji exact inquiry, 'that this vegeta- 

 ble fragment issued from a leaf of the family Monocotyledon, probably not from a 

 })alm-tree, but from a Pardanacese or Scitaminese' — consequently, from trees belong- 

 ing to the tropical regions. Now I am sure it comes from the tropics, I am greatly 

 surprised to perceive that a piece of leaf of this dimension could run oif a distance 



