THE GULF STREAM. 2OQ 



Herschel does not find an answer to the main objec- 

 tions urged by Maury against the trade- wind theory. 

 Content with urging an apparently unanswerable objec- 

 tion against his opponent's view, he leaves his own to 

 take care of itself. 



In forming an opinion respecting the two theories, 

 one is struck with the immense superiority in the power 

 of Maury's agent. For, if we consider, we shall see that 

 almost the whole of the sun's action upon the ocean 

 goes to produce those variations in temperature and 

 saltness in which Maury sees the origin of the current- 

 system ; but a very moderate portion of the sun's action 

 is called into play in the production of the trade-wind^. 

 Now it is very doubtful whether any large proportion 

 even of the force expended in producing the trade-winds, 

 ever acts on the water. For we know that the north- 

 easterly and south-easterly air-currents of the northern 

 and southern hemispheres, do not wholly merge into 

 northern and southern currents meeting point-blank 

 near the equator, as Herschel's theory seems to imply. 

 On the contrary, there is a wide zone of calms at the 

 equator, and the two systems of trade-winds appear to 

 pass upwards above the calm air, without parting with 

 the whole of their easterly motion. When once they 

 begin to travel polewards, they lose their easterly motion 

 in the same way that they acquired it that is, through 

 the effects of the earth's rotation. And whatever portion 

 is lost in this way which, for aught we know, may be 

 a very considerable portion cannot be taken into 



