368 THE DEPTHS OF THE SEA. [CIIAP, VIII. 
7 
be true, or neither; but it is logically impossible that 
both of these can, for the simple reason that the 
waters of the equator cannot at the same time be 
both lighter and heavier than the water at the poles.” 
“So long as the two causes continue in action, no 
eurrent can arise unless the energy of the one cause 
should happen to exceed that of the other, and even 
then a current will only exist to the extent by 
which the strength of the one exceeds that of the 
ouher.; 
It seems scarcely necessary to enter further into 
detail in reference to Captain Maury’s theory of ocean 
currents, which is really chiefly remarkable for its 
ambiguity, and for the pleasant popular style in 
which it is advocated; since my friend and _ col- 
league Dr. Carpenter has latterly brought into great 
srominence what appears to be a modification of the 
same view, put in a more definite form. 
Professor Buff, in his excellent little volume on the 
Physics of the Earth, speaking of the layer of cold 
water derived from the Arctic seas which underlies 
the tropical ocean, and its method of transport, says: 
“The following well-known experiment clearly illus- 
trates the manner of the movement. A glass vessel 
is to be filled with water with which some powder 
has been mixed, and is then to be heated at bottom. 
You will soon see, from the motion of the particles 
of powder, that currents are set up in opposite direc- 
tions through the water. Warm water rises from the 
bottom, up through the middle of the vessel, and 
spreads over the surface ; while the colder, and there- 
fore heavier liquid, falls down at the sides of the 
1 James Croll, op. cit. 
