§ 288. KAINS AND RIVERS. 109 



for parallel, from tlie equator to 40° or 45° S., the southern hemi- 

 sphere is the cooler. This fact is consistent with the supposition 

 that the heat which is rendered latent and abstracted from that 

 hemisphere by its vapors is set free by their condensation in this. 

 Upon no other hypothesis than by these supposed crossings can 

 this fict be 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 hydrometerf (§ 285) for every parallel of latitude 

 in the Atlantic Ocean from 40° S. to 40° IST., show that, parallel 

 for parallel, and notwithstanding 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 sea on different sides of the line is reconciled by 

 the hypothesis which requires a crossing at the calm belts. The 

 vapor which conveys fresh water and caloric from the southern 

 hemisphere to the northern will in part account for this differ- 

 ence both of specific gravity and temperature, and no other h}^- 

 pothesis will. This hydrometric difference indicates the amount 

 of fresh water which, as vapor in the air, as streams on the land, 



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 our 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 

 cf Africa is too northerly to bring this fragment to the finding-place in 25° N. and 

 38° y^:'— 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 iden- 

 tically the same ; yet within certain latitudes the southern hemisphere is, parallel 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 eifccts, and were it so, the southern hemisphere would be gradually 

 growing cooler. There is no evidence that it is so growing, and the inference tliat 

 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 south- 

 ern has more water and more clouds — clouds prevent radiation — therefore the south- 

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

 paradox to be reconciled but upon the supposition that the southern surplusage is 

 stowed away in vapors, transported thence across the calm belts by the winds, and 

 liberated by precipitation on our side of the equator ? 



"t Rodgers, in the Vincennes. Maury's Sailing Directions, 8th ed., vol. i., p. 235. 



