CHAP. VIII. ] THE GULF-STREAM. 377 
produce any current whatever;' 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;’ 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. 
