CROLL ON CLIMATE AND TIME. 721 



conveyed and distributed by each cubic foot of water is 1,158,000 

 foot-pounds,' and by the whole volume of Gulf-Stream water there is 

 transferred every day from the equatorial regions 77,470,650,000,000,- 

 000,000 foot-pounds of heat. But these figures convey no definite 

 impression of the vastness of the results. It is equal to one-fourth 

 of all the heat received from the sun by the whole Atlantic Ocean 

 from the Tropic of Cancer to the Arctic Circle, raising the tempera- 

 tui'e of its waters .one-fifth it is equal to about one-half the solar heat 

 Avhich falls upon the entire arctic regions. Under the equator there 

 comes from the sun on each square foot of surface about 83 foot-pounds 

 of heat every second, when the sun is in the zenith. Twenty-two per 

 cent, of this is absorbed by the atmosphere ; the remainder falls as 

 heating-power upon the ocean. Now, the quantity conveyed is equal 

 to all that thus falls upon 1,560,935 square miles of surface. If this 

 source of heat be destroyed or turned away, the area of arctic winter 

 would rapidly extend southward, covering England, both Old and 

 New, with ice which the heat of summer would not remove. 



Nor would any conceivable movements of the atmosphere supply 

 the deficiency of heat. For not only does heated air at the equator 

 rise, and radiate its heat in the cold regions of the upper atmosphere, 

 but the capacity of air for heat is much less than water. So great is 

 the diiFerence in this respect that the Gulf Stream conveys as much 

 heat as a current of air would if 3,234 times as large, of the same 

 temperature, and moving with the same velocity. The heated air, 

 however, which rises at the equator is charged with vapor, and in the 

 opinion of Sir John Herschel this vapor, conveyed by the upper or 

 anti-trades, is condensed in the temperate and arctic regions, greatly 

 modifying their temperature. To the extent that the vapors are thus 

 conveyed, the conclusion of Sir John is correct ; for, as Prof. Tyndall 

 has shown, in the conversion of one pound of aqueous vajDor into water 

 there is given out as much heat as is sufficient to melt five pounds of 

 cast-iron. But Mr. CroU proves that the greater part of the vapor 

 raised in the equatorial regions falls there as rain ; that the upper 

 winds are dry, and gather moisture only when they again reach the 

 earth and become surface-winds in the temperate and arctic zones. 



If all currents of the ocean and atmosphere should cease, no heat 

 could be transferred from the equatorial to the arctic regions, and 

 temperatures would depend on the solar heat falling in the respective 

 latitudes. The equatorial and arctic regions would become uninhab- 

 itable, the mean temperatures rising to 136 Falir. in the one, and 

 sinking to 83 below zero in the other. The present difference of 80 

 would be increased to 218, and only a narrow zone of temperate cli- 

 mate would prevail. 



^ A foot pound is the amount of heat-force expended in raising one pound one foot; 

 772 foot-pounds is the equivalent of the heat that will raise one pound of water one degree 

 of temperature. 



VOL. Til. 46 



