399 
of Edinburgh, Session 1876 - 7 7 . 
rising of the glacial water under the equator. He considers that 
the rising of the glacial water under the Line is due to the meeting 
of the Arctic and Antarctic underflows. That part of the effect is due 
to this cause is very probable, but when we consider the very great 
area of section of the under glacial currents, and the small amount 
of water that can be carried by them, it is evident that their rate 
of motion must be very slow, and it is very doubtful how far the 
whole phenomena can be explained in this way. Our doubts on 
this subject are somewhat confirmed by the consideration of the 
fact that the Arctic underflow is warmer than the Antarctic under- 
flow, and would therefore — other things being equal — tend simply 
to overflow the Antarctic underflow, and not to rise vertically as 
Dr Carpenter supposes. That the wind-driven currents, so long 
as they are increasing in volume, have the power of drawing the 
bottom water upwards cannot be doubted, and I have already said 
was most marked in the experimental illustration. We should not, 
however, expect to find this lifting power so marked in the ocean, 
as the ocean currents are so much deeper and do not so rapidly 
increase in volume as in the experiment. And further, the bottom 
water in the ocean is denser than the surface water, and does not 
rise so easily as the bottom water in the experiment. 
If we take the evidence of the temperature sections of the At- 
lantic on the subject, we shall find that they also point to the wind 
as one of the causes of the rising of the cold bottom water. If we 
take the section between Madeira and lat. 3° N. and long. 15° W, 
we find that the isotherm of 40°, which at Madeira lies at a depth 
of about 900 fathoms, rises to a depth of only 300 fathoms at the 
equatorial position, and further, neither this section nor the section 
between lat. 3° N. and long. 15° W. and Pernambuco, show the 
least evidence of the presence of Antarctic water so far north as 
the equator, in the eastern basin of the Atlantic. This rising , 
then , of the glacial water on the eastern side of the Atlantic cannot 
therefore be due to the meeting of the glacial streams , and in the 
absence of further evidence we may suppose it to be due to the 
wind-driven currents. We thus see, that though the great bulk of 
the wind-driven circulation is a horizontal one, yet there is also 
produced in a comparatively very small degree a modified vertical 
circulation. 
3 g 
VOL. IX. 
