368 T. C. CHAM BERLIN 



of the past and give us a new means of forecast of climatic states in 

 the future. 



That the deep-sea circulation is now actuated dominantly by 

 polar agencies is clear from the low temperatures of the abysmal 

 waters, even beneath the tropics. It is a firm inference that cold 

 waters creep slowly along the depths from the polar seas equator- 

 ward, where they gradually rise to the surface and return on more 

 superficial routes. This is not, however, yet a matter of observation, 

 and the courses pursued are unknown. It is perhaps more probable 

 that they are gyratory or spiral and complex than that they are sim- 

 ple and direct. 



The agencies that affect oceanic circulation include at least (i) 

 wind, (2) atmospheric transfer,- (3) differences of sahnity, and (4) 

 differences of temperature, including freezing and thawing. The 

 earth's rotation, of course, modifies the currents, but does not actu- 

 ate them, 



1. The effect of the wind is superficial and familiar, and need 

 only be considered here in so far as it affects the deep-sea circula- 

 tion. Its currents constitute horizontal circuits, and their frictional 

 effect upon the deep currents is probably slight and of a gyratory 

 phase in the main. In so far as they are strictly horizontal, they 

 doubtless favor equally poleward and equatorward movement in the 

 abysmal waters. If there is a component of their sum-total that 

 favors the piling up of waters in the polar regions, it must favor the 

 present deep circulation. If the opposite is true, it must antagonize 

 it. There seems no way at present to measure the relative amounts 

 of these opposing tendencies. It is plausible enough to reason that 

 the cold air from the polar regions would flow more largely at the 

 base of the atmosphere than would the warmer air from the equa- 

 torial regions, and that the polar winds would thus antagonize the 

 present abysmal circulation. But theoretical deductions are rarely 

 sure-footed in these complex subjects. The balance of influence 

 whatever it may be, is probably so slight as to be negligible. 



2. ■ We cannot here attempt to follow empirically the transfers of 

 water by evaporation and precipitation, but general inspection seems 

 to indicate the nature of the average effect. The saturation point of 

 the atmosphere falls progressively from the equator to the poles, and 



