398 
Proceedings of the Royal Society 
at a depth of nearly 1000 fathoms, rises to about 700 fathoms be- 
fore it arrives at St Thomas. Again, in the passage north from St 
Thomas to Bermuda, and on to Halifax and New York, the tem- 
perature sections show that after getting out of the region of the 
trade winds, the drifted hot surface water has gradully lost its 
motion and increased in depth. This refers to the great mass of 
ocean water, and not to the comparatively shallow Gulf-Stream. 
For instance, the isotherm of 60°, which at St Thomas was found 
at a depth of only 200 fathoms, was found at a depth of 330 
fathoms for hundreds of miles all round Bermuda, notwithstanding 
a considerable reduction in the temperature of the surface water. 
The temperature sections of the South Atlantic do not illustrate 
these points so well as the temperature sections of the North 
Atlantic, partly because a very large part of the hot surface water 
of the south equatorial current does not return to the South Atlan- 
tic, but is driven into the North Atlantic, and partly on account of 
the great amount of cold surface water of the Antarctic drift, which 
gets mixed up with the return current; and further, the temperature 
sections are not taken at the best places for our present purpose. 
The only two available sections, however, point to the same con- 
clusion as the North Atlantic sections. There is no section of the 
south equatorial current, but we may suppose it to be somewhat 
similar to the section taken between St Paul’s Rocks and Per- 
nambuco, which gives the isotherms of the branch of the south 
equatorial current which passes into the North Atlantic. If we 
compare this section with the part of the stream which has flowed 
southwards, as given in the section taken between Abrolhos Island 
and Tristan d’Acunha, we find that the hot surface water, in flowing 
southwards beyond the region of the south-east trade winds, has 
deepened, notwithstanding a considerable fall in the temperature of 
the surface water. The isotherm of 40° which was found at a depth 
of 300 fathoms off Pernambuco, sunk to a depth of between 400 
and 500 fathoms between Abrolhos Island and Tristan d’Acunha. 
We might have expected that this hot surface water would have 
kept its depth all the way to the Cape of Good Hope. It, however, 
does not do so, probably on account of the cold surface water of the 
Antarctic drift. 
I am aware Dr Carpenter has offered a different explanation of the 
