110 PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY. 



Ocean. If this be so, it mnst cross one or more of the calm belts.* 

 (4.) Parallel for parallel, the southern hemisphere from the equator 

 to 40° or 45° S., is the cooler. This fact is consistent with the suppo- 

 sition that the heat that is rendered latent and abstracted h'om that 

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

 Upon no other hypothesis than by these supposed crossings can 

 this fact be reconciled, for the amount of heat annually received 

 jfrom the sun by the two hemispheres is, as astronomers have 

 shown, precisely the same.t (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 notwithstanding the difference of temperature, 

 the specific gravity of sea-water is greater in the southern than it 



* After this liad been wTitten, 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 a piece of vegetable substance caught 

 in a small sack (hoisted up above the tops) between 22^-25^ lat. N., and 380-39Jo 

 long, W. This piece is of the following dimensions : 14 millim, long, 1 to 1| mm. 

 large, i mm. thick, and weighing 1^ milligrams. Our famous microscopist and 

 naturalist, Professor P. Harting, at IFtrecht, told me, after an exact inquiry, ' that 

 this vegetable fragment issued from a leaf of the family Monocotjdedou, probably 

 not from a palm-tree, but from a Padanacese or Scitaminese ' — consequently, from 

 trees belonging 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 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 25° N. and 38° W." — Letter from 

 Lieut. Andrau, of the Dutch Navy, dated Utrecht, Jan. 2, 1860. 



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

 identically 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 effects, and were it so, the southern hemi- 

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

 growing, and tlie 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 nortliern 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 re- 

 conciled but upon the supposition that the southern surplusage is stowed away in 

 vapours, transported thence across the calm belts by the winds, and liberated by ' 

 precipitation on our side of the equator ? 



X Kodgers, in the Vincennes. Maury's Sailing Directions, 8th ed., vol. i., p. 235* 



