CHAP, vm.] THE GULF-STREAM. 377 



produce any current whatever ; l but in this view he 

 does not certainly receive universal support. I am 

 myself inclined to believe that in a great body of 

 salt water at different temperatures, with unequal 

 amounts of evaporation, under varying barometric 

 pressures, and subject to the drift of variable winds, 

 currents of all kinds, great and small, variable and 

 more or less permanent, must be set up ; 2 but the 

 probable result appears to be reduced to a minimum 

 when we find that causes, themselves of doubtful 

 efficiency, actually antagonize one another ; and that 

 we are obliged to trust for the final effect to the 

 amount by which the least feeble of these exceeds 

 the others in strength. Speaking in the total ab- 

 sence of all reliable data, it is my general impres- 

 sion that, if we were to set aside all other agencies, 

 and to trust for an oceanic circulation to those con- 

 ditions only which are relied upon by Dr. Carpenter, 

 if there were any general circulation at all, which 

 seems very problematical, the odds are rather in 

 favour of a warm under-current travelling north- 

 wards by virtue of its excess of salt, balanced by a 

 surface return-current of fresher though colder arctic 

 water. 



With regard, then, to this question of a general 

 circulation caused by difference in specific gravity, 

 for the present I cordially endorse the opinion ex- 

 pressed by the late Sir John Herschel in a cautious 



1 James Croll, op. cit. 



2 On the Distribution of Temperatures in the North Atlantic. 

 An Address delivered to the Meteorological Society of Scotland at 

 the General Meeting of the Society July 5th, 1871, by Professor 

 Wyville Thomson. 



