W. Ferret — Relative T< //<j» r><t>' r>.« of 'the Hemispheres. 91 



ocean currents from the equator toward the poles, while in 

 the latter the well-kno .ange of water between 



the equatorial and polar regions, arising from a difference of 

 temperature, conveys a great amount of heat from the former 

 to the latter. iperatnre in the lower latitudes- 



and increasing it in the higher ones. It has been estimated 

 that the heat transferred from the torrid zone to higher lati- 

 tudes by the Gulf Stream alone amounts to about one-twelfth 

 of all the heat received by the earth from the sun between the 

 equator and the tropic of Cancer, and that transferred by the 

 Kuro-siwo to more than twice as much more. If all the heat 

 received by the torrid zone had to be disposed of by radiation 

 back into space, of course the temperature there would be 

 higher, since by the law of radiation, where greater radiation 

 is required, there must be a higher temperature of the radiating 

 surface. On the other hand, if no heat were received in the 

 polar zone, or higher latitudes, except that received directly 

 from the sun, the temperature at which the radiating surface 

 would have to stand to dispose of the heat received would be 

 less. We see the effect upon temperature of this transfer of 

 heat from equatorial to polar regions in the relative mean tem- 

 peratures of land and water in the northern hemisphere. In 

 the lower latitudes mean ocean temperatures are lower, and in 

 the higher latitude <±\-iwu-\\ than on land. And the differences 

 would be still greater, if much of the heat conveyed by ocean 

 currents to the higher latitudes were not transferred to the 

 land by the general eastward motion of the air in those lati- 

 tudes. 



Since the amount of transfer of heat from equatorial to polai 

 regions must be somewhat in proportion to the amount of 

 ocean surface, the amount of this transferrence must be greater 

 in the southern than in the northern hemisphere. Hence the 

 difference between the mean temperature of the equatorial and 

 polar regions must be less in the southern than in the northern 

 v. If the mean temperatures of the two hemispheres 

 are equal, as has been shown, it is readily seen that the effect. 

 of this must be to make the temperature of the lower latitudes 

 colder, and that of the higher latitudes warmer, in the southern 

 hemisphere than in the northern. 



It is well known that the annual amount of heat received 

 from the sun by each hemisphere is precisely the same. A 

 number of hypotheses have therefore been devised to account 

 for the supposed difference of temperature between the two 

 hemispheres. Poisson supposed it was due to the greater heat- 

 absorbing power of land than of water, which, on account of 

 the greater proportion of land in the northern than in the 

 southern hemisphere, would cause the temperature of the 



