CHAP. VIII.] THE GULF-STREAM. 397 
The North Atlantic and Arctic seas form together 
a cul de sac closed to the northward, for there is 
practically no passage for a body of water through 
Behring’s Strait. While, therefore, a large portion 
of the water, finding no free outlet towards the 
north-east, turns southward at the Acores, the re- 
mainder, instead of thinning off, has rather a ten- 
dency to accumulate against the coasts bounding 
the northern portions of the trough. We accordingly 
find that it has a depth off the west coast of Iceland 
of at least 4,800 feet, with an unknown lateral 
extension. Dr. Carpenter, discussing this opinion, 
says: ‘It is to me physically inconceivable that 
this surface film of lighter (because warmer) water 
should collect itself together again—even supposing 
it still to retain any excess of temperature—and 
should burrow downwards into the ‘trough,’ dis- 
placing colder and heavier water, to a depth much 
ereater than that which it possesses at the point of 
its greatest ‘ glory ’"—its passage through the Florida 
Narrows. The upholders of this hypothesis have to 
explain how such a re-collection and dipping-down 
of the Gulf-stream water is to be accounted for on 
physical principles.’ I believe that, as a rule, 
experimental imitations on a small scale are of little 
use in the illustration of natural phenomena; a very 
simple experiment will, however, show that such a 
process is possible. If we put a tablespoonful of 
cochineal into a can of hot water, so as to give it 
a red tint, and then run it through a piece of india- 
rubber tube with a considerable impulse along the 
surface of a quantity of cold water in a bath, we see 
1 Dr. Carpenter’s Address to Geographical Society, op. cit. 
