132 LIGHT SCIENCE FOR LEISURE HOURS. 



heat upon the equatorial waters. He argues thus : 

 Granting that these waters become lighter and expand 

 in volume, yet they can only move upwards, down- 

 wards, or sideways. There can be nothing to cause 

 either of the two first forms of motion; and as for 

 motion sideways, it can only result from the gradual 

 slope caused by the bulging of the equatorial waters. 

 He proceeds to show that this slope is so slight that 

 we cannot look upon it as competent to form any 

 sensible current from the equatorial towards the polar 

 seas. And even if it could, he says, the water thus 

 flowing off would have an eastward instead of a 

 westward motion, precisely as the counter-trade-winds, 

 blowing from equatorial to polar regions, have an east- 

 ward motion. 



It is singular how completely the supporter of each 

 rival view has succeeded in overthrowing the argu- 

 ments of his opponent. Certainly Maury has shown 

 with complete success that the inconstant trade- winds 

 cannot account for the constant Gulf current, which 

 does not even flow before them, but, in places, exactly 

 against their force. And the reasoning of Sir John 

 Herschel seems equally cogent, for certainly the flow 

 of water from equatorial towards polar regions ought 

 from the first to have an eastward, instead of a west- 

 ward motion ; whereas the equatorial current, of which 

 the Gulf Stream is but the continuation, flows from 

 east to west, right across the Atlantic. 



Equally strange is it to find that each of these emi- 

 nent men, having read the arguments of the other, 



