^CA6. SEA ROUTES, CALM BELTS, ETC. 3-(:7 



dispensed by radiation is very much greater on one side of the 

 equator than the other. The total eifect of the alternate cooling 

 down on each side of the equator causes an accumulation of ice at 

 the pole — when the nights are longest — sufficient, say they, to dis- 

 turb the centre of gravity of the earth, causing it to take up its po- 

 sition on the icy side of the equator. As the ice accumulates, so 

 is the water drawn over from the opposite hemisphere. Such, 

 briefly stated, is the theory which has found very ingenious and 

 able advocates in the persons of MM. Julien- and Adhemar.f 



64:6. This theory is alluded to here, not for the purpose of dis- 

 Are the climates of the cussiou, but for thc purposc of directing attention 

 earth ciianging? ^^ Certain parts of this work in connection with it, 

 as Chapters VII. and XXI., for example, and of remarking upon 

 the stability of terrestrial climates. Though the temperate re- 

 gions be cooler in the southern than in the northern hemisphere, 

 it does not appear certain that the climates of the earth are nov^ 

 changing. Observations upon the subject, however, are lacking. 

 The question is one of widespread and exceeding interest ; and it 

 may be asked if we have not in the strength of the trade-winds a 

 gauge, or in their barometric weight an index, or in the equatorial 

 calm belt a thermometer — each one of the most delicate construc- 

 tion and sensitive character — which would, within the compass of 

 human life, afford unerring indications of a change of climates, if 

 any such change were going on? If the temperature of the S.E. 

 trade-winds, or the barometric pressure upon the N.E. (§ 64:1). 

 were to be diminished, the S.E. trades would force this calm belt 

 still farther to the north, and we might have a regular rainy sea 

 son in w^hat is now the great desert of Sahara ; for where this calm 

 belt is (§ 517) there is the cloud-ring, with its constant precipita- 

 tion. Therefore, if there be any indications that the southern edge 

 of the great desert is gradually approaching the equator, it favors 

 the supposition that the southern hemisphere is growing warmer ; 

 but if the indications be that the southern edge of the desert is 

 receding from the equator, then the fact would fovor the supposi- 

 tion that the southern hemisphere is growing still cooler. Kor 



* Courants et Revolutions de I'Atmosphere et de La Mer, comprenant une theo- 

 rie nouvelle sur les Deluges Periodiques. Par Felix Julien, Lieutenant de Vaisscau, 

 etc. Paris, 1860. 



t Revolutions de La Mer. Deluges Periodiques. Vav J. Adh'mar. Paris, 18G0. 



