CHAP. viii. J THE GULF-STREAM. 375 



the level of the polar water being reduced, and its 

 density increased by the surface-cold to which it is 

 subjected, whilst a downward motion is also imparted 

 to each stratum successively exposed to it ; and the 

 level of equatorial water being raised and its density 

 diminished by the surface-heat to which it is exposed. 

 (The first of these agencies is by far the more effec- 

 tive, since it extends to the whole depth of the water, 

 whilst the second only affects, in any considerable 

 degree, the superficial stratum.) Thus a movement 

 will be imparted to the upper stratum of oceanic 

 water from the equator towards the poles, whilst a 

 movement will be imparted to the deeper stratum 

 from the poles towards the equator." 



It seems to me that the doctrine here propounded 

 by my distinguished colleague, if I understand it 

 aright, is open to the objection to which I have 

 already referred in connection with the speculations 

 of Captain Maury. 



If the currents flow in the direction and with the 

 permanence accepted by Dr. Carpenter in the Strait 

 of Gibraltar and in the Baltic Sound, if their flow 

 and its direction be due to the causes to which Dr. 

 Carpenter attributes them, and if there be any 

 analogy whatever between the conditions of equi- 

 librium of these inland seas and that of the outer 

 ocean, none of which propositions appear to me at 

 all satisfactorily proved, I should think that the vast 

 equatorial region, the path of the trade-winds and the 

 belt of vertical solar radiation, must, so far as eva- 

 poration is concerned, resemble, or rather greatly 

 exaggerate, the conditions of the Mediterranean. The 

 consequent accumulation of salt, through the whole 



