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Proceedings of the Boyal Society 
“warm” areas respectively, but during these early investigations, 
there seems to have been no suspicion that these two areas might be 
separated by a submarine barrier. Two bodies of water, differing 
from one another by 14° Fahr., were, at this early stage of deep-sea 
investigations, even regarded as abutting against one another with- 
out any intervening barrier. Professor Wyville Thomson says : — 
“ In the Faroe Channel 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 Faroe Chan- 
nel. What prevents the cold water from slipping, by virtue of its 
greater weight, under the warm water off the Butt of the Lews 1 
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, com- 
pelling it to follow that particular course ” ( Depths of the Sea , 
p. 395). 
II. Origin and Objects of the “ Knight Errant ” 
Investigations. 
How these early trips of the “Lightning” and “ Porcupine ” in 
1868-69 led to the equipment of the “Challenger” for a circum- 
navigating cruise is now a matter of history. One or two general 
considerations with regard to the movements of ocean water, which 
were established by the “Challenger” observations, may be here 
referred to, as having led to a reinvestigation of the Faroe 
Channel. 
The waters of the ocean are everywhere in a state of movement, 
— not a mere state of oscillation by the tides, not a surface movement 
by shifting winds, — but a steady massive movement, affecting the 
ocean throughout its whole extent and depth. 
The deeper currents are in general so slow that it is impossible 
to detect their movement directly by the current drag, or any other 
instrument which has yet been constructed. By means of the 
thermometer, however, these deep currents can be traced to their 
source, and their depth and direction determined. 
