EAINS AND EIVERS. 115 



(4.) Parallel fur parallel, the southern hemispliere from the 

 equator to 40° or 45° S., is the cooler. This fact is consistent 

 with the supposition that the heat that is rendered latent and 

 abstracted from that liemisphere by its vapours is set free by 

 their condensation in this. Upon no other hypothesis than by 

 these supposed crossings can this fact he reconciled, for the 

 amount of heat annually received from the sun by the two' 

 hemispheres is, as astronomers have shown, precisely the same.* 

 (5.) Well-conducted observations made with the hydrometer | 

 (§ 285) for every parallel of latitude in the Atlantic Ocean from 

 40° S. to 40° N., show that, parallel for parallel, and notwith- 

 standing the difference of temperature, the specific gravity of 

 sea-water is greater in the southern than it is in the northern 

 hemisphere. This difference as to the average condition of the 



1 to IJ mm. largo, i mm. thick, and weighing 1 J milligrams. Our famous 

 microscopist and naturahst, Professor P. Harting, at Utrecht, told me, after an 

 exact inquiry, ' that this vegetable fragment issued from a leaf of the family 

 Monocotyledon, probably not from a palm-tree, but from a Padanacege or 

 Scitaminese' — consequently, from trees belonging to the tropical regions. Now 

 I am sure it comes fi-om the tropics. I am greatly surprised to perceive that a 

 piece of leaf of this dimension could run off a distance of more than 1200 

 geographical miles in the upper regions of the atmosphere ; for the nearest 

 coast-lines of the two continents, America and Africa, lay at the said distance 

 from the place where this vegetable fragment was caught, by the carefulness of 

 Capt. S. Stapert, one of the most zealous co-operators. There can be no doubt 

 that it comes from South America, because the direction of the trade-winds on 

 the west coast of Africa is too northerly to bring this fragment to the finding- 

 place in 2o° N. and 38° W." — Letter from Lieut. Andrau, of the Dutch Navy, 

 dated Utrecht, Jan. 2, 1860. 



* The amount of solar heat annually impressed upon the two hemispheres is 

 identically the same ; yet within certain latitudes the southern hemisphere is, 

 paralled for parallel, the cooler. How does it become so ? If it be the cooler 

 by radiation, then it must be made so by radiating more heat than it receives ; 

 such a process would be cumulative in its effects, and were it so, the southern 

 hemisphere would be gradually growing cooler. There is no evidence that it is 

 so growing, and the inference that it is seems inadmissible. In fact, the 

 southern hemisphere radiates less heat than the northern, though it receives 

 as much from the sun. And it radiates more, for this reason : there is more 

 land in the northern — land is a better radiator than water — therefore the 

 northern radiates more heat than the southern hemisphere ; the southern has 

 more water and more clouds— clouds prevent radiation— therefore the southern 

 hemisphere radiates less heat than the northern ; still it is the cooler. How is 

 this paradox to be reconciled but upon the supposition that tlie southern sur- 

 plusage is stowed away in vapours, transported thence across the calm belts by 

 the winds, and liberated by precipitation on our side of the equator ? 



t Rodgcrs, in the Vinceunes. Mamy's Saihug Directions, Stli ed., vol. i.,p. 235. 



i2 



