Note 13 — Chapter II · OCEANS-CURRENTS IN RELATION TO THE DISTRIBUTION OF HEAT OVER THE GLOBE.
Reading edition
It is probable that a large proportion of the water constituting the south-eastern branch of the Gulf-stream is never cooled down to 40°; but, on the other hand, the north-eastern branch, which passes into the arctic regions, will be cooled far below 40°, probably below 30°. Hence I cannot be over-estimating the extent to which the water of the Gulf-stream is cooled down in fixing upon 40° as the average minimum temperature.