384 THE DEPTHS OF THE SEA. [CHAP. VIII. 
to it. But as for the seat of the forces which put 
and keep the Gulf-stream in motion, theorists may 
place them exclusively on one side of the ocean with 
as much philosophical propriety as on the other. 
Its waters find their way into the North Sea and 
Arctic Ocean by virtue of their specific gravity, while 
water thence, to take their place, is, by virtue of its 
specific gravity and by counter-currents, carried back 
into the gulf. The dynamical force which causes the 
Gulf-stream may therefore be said to reside both in 
the polar and in the intertropical waters of the 
Atlantic.” 
According to this view, the tropical water finds its 
way on account of its greater weight towards the poles, 
while the polar water, owing to its less weight, moves 
southwards to replace it. The general result would 
be of course a system of warm under- and cold 
surface-currents, and these we do not find. I merely 
quote the passage as a curious illustration of the 
adage that on most questions a good deal can be 
said on both sides. 
We have already considered the doctrine of a general 
oceanic circulation, which has been so strongly ad- 
vocated of late by Dr. Carpenter, and I have merely 
to advert in this place to the bearing which that 
doctrine has upon our views as to the origin of the 
Gulf-stream ; its bearings on the extension and dis- 
tribution of the current will be discussed hereafter. 
As already stated, Dr. Carpenter attributes all the 
great movements of ocean water to a general con- 
vective circulation, and of this general circulation 
he regards the Gulf-stream as a peculiarly modi- 
fied case. In the passage already quoted (p. 370) of 
