THE GULF STREAM. 255 
tradewinds in originating the oceanic circulation of the Atlan- 
tic. That winds blowing steadily from one quarter give rise to 
powerful currents is well kow, and it is not difficult | to imagine 
the prominent part the trades must play in setting in motion, 
in a southwesterly and a northwesterly Ten, the mass of 
water over which they sweep so persistently on each side of the 
equator. 
The change 
ing of the monsoons is well known. 
of currents in the Indian Ocean due to the shift- 
How far below the surface 
this action of the winds reaches, is another question.’ Theo- 
retically it has been calculated by Zoeppritz that one hundred 
thousand years is ample time to allow the friction of the parti- 
cles to extend from the surface to the bottom, say to two thou- 
sand fathoms, were the winds to blow without intermission in 
one direction during that time, with the : average power they are 
known to possess.” 
We may imagine the whole of the mass of the Atlantie within 
the belt of the tradewinds to be moving in a westerly direction, 
and impinging upon the continental slope of South Americ: 5 
and. upon the Windward Islands; at which point it is deflected 
either in a southerly or northerly direction, or forces its way 
into the Caribbean. In our present state of knowledge it is 
difficult to trace the path of the equatorial water as it is forced 
into the eastern Caribbean. Commander Bartlett supposes that 
it is warmed. in the Caribbean by circulating round the whole 
basin. The water which is swept into the Caribbean by the 
tradewinds through the passages between the Windward Islands, 
and being then driven into the Old Bahama Channel funnel, 
! The movement arising from the ac- the conditions producing them (acting 
tion of the winds on the surface is trans- 
mitted by frietion from one layer to an- 
other, and communicates 
the upper 
layers in succession. 
the velocity of 
particles to the underlying 
IE this is continued 
of the lowest 
layers will equal within a fraction that of 
the upper layer. 
2 [t is therefore possible that currents, 
long enough, the velocity 
which owe their existence to causes that 
have been modified to a certain extent, 
should still exist in the ocean long after 
from the surface) have ceased to be effee- 
tive by any break of continuity due to the 
interposition of islands or of banks in 
the 
3 Did the Gulf Stream not meet conti- 
track of oceanic currents. 
nental masses, it would simply expand 
north and south, losing its initial velocity, 
the 
poles ; the cold penetrating all the deeper 
find it 
summits that rise 
and gradually cool down towards 
portions of the ocean, 
the 
above the line of perpetual snow. 
just as we 
reaching higher 
