CHAP. VIII. ] THE GULF-STREAM. . 395 
since they give us the depth and volume of the mass 
of water which is heated above its normal tempera- 
ture, and which we must regard as the softener of 
the winds blowing on the coasts of Europe. Refer- 
ring to Fig. 60, in the Bay of Biscay, after passing 
through a shallow band superheated by direct radia- 
tion, a zone of warm water extends to the depth of 
800 fathoms, succeeded by cold water to a depth of 
nearly two miles, In the Rockall channel (Fig. 59) 
the warm layer has nearly the same thickness, and 
the cold underlying water is 500 fathoms deep. Off 
the Butt of the Lews (Fig. 56) the bottom tem- 
perature is 5°2 C. at 767 fathoms, so that there 
the warm layer evidently reaches to the bottom. 
In the Fwroe channel (Fig. 55) the warm water 
forms a surface layer, and the cold water underlies 
it, commencing at a depth of 200 fathoms,—567 
fathoms above the level of the bottom of the warm 
water off the Butt of the Lews. The cold water 
abuts against the warm—there is no barrier between 
them. Part of the warm water flows over the 
cold indraught, and forms the upper layer in the 
Fééroe channel. What prevents the cold water from 
slipping, by virtue of its greater weight, under the 
warm water off the Butt of the Lews? It is quite 
evident that there must be some force at work 
keeping the warm water in that particular position, 
or, if it be moving, compelling it to follow that 
particular course. The comparatively high tem- 
perature from 100 fathoms to 900 fathoms I have 
always attributed to the northern accumulation of 
the water of the Gulf-stream. The amount of heat 
derived directly from the sun by the water as it 
