CHAP. viiT.] THE GULF-STREAM. 395 



since they give us the depth and volume of the mass 

 of water which is heated ahove its normal tempera- 

 ture, and which we must regard as the softener of 

 the winds blowing on the coasts of Europe. Refer- 

 ring to Pig. 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 Faeroe 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 

 Faeroe 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 



