22 THE OCEAN WORLD. 
character of its waters would be completely changed—if they were 
fresh in place of salt. ‘“ Let us imagine,” says M. Julien, “that the 
sea, now entirely composed of fresh water, of one uniform tempera- 
ture from the Pole to the Equator, and from the surface to its 
greatest depths; the solar heat would penetrate the liquid beds 
nearest to the Equator ; it would dilate them, so as to raise them. 
above their primitive level ; by the single effect of gravitation, they 
would glide on the surface towards the Polar zones. The absence of 
all solar radiation would tend, on the contrary, to cool and contract 
them without this tendency. An exchange would be established 
from the extremities towards the centre; in other words, a counter 
current of cold and heavy water, calculated to replace the losses 
occasioned by the action of solar radiation, would descend from 
the Poles, but quite maintaining itself beneath the light and warm 
current from the Equator.” 
In a like system of general circulation, the physical properties of 
pure water, which attains its maximum of density 7° 2” F. below 
zero, would produce the most singular consequences. As its tem- 
perature rose above that point, the water would become lighter, 
having consequently a tendency to ascend towards the upper beds. 
After this, the equatorial current, meeting in its progress towards the 
Poles the cold water, would itself be cooled down ; and when its 
temperature had reached 4° below zero, being now heavier than the 
polar current, would change places with it, descending until it reached 
water equally dense, while the polar current would ascend. Hence 
would arise a sort of confusion of currents, which would give to a 
fresh-water ocean the strangest results, disarranging every instant the 
regular circulation of its waters. It could not be so, however, in an 
ocean of salt water, which attains its maximum specific gravity at 
4° 8" below zero. By evaporation at the surface it is concentrated 
and precipitated, and thus rendered denser than that immediately 
below the surface. It consequently sinks, while the lower beds come 
up to replace, in order to modify it, and in turn to be precipitated in 
the same manner. “ In this manner we find established a continually 
ascending and descending movement, which carries down into the 
depths of ocean the water warmed at the surface by the solar rays of 
the Torrid zone. This double vertical current facilitates and pre- 
pares. the grand horizontal current which puts these submarine 
reservoirs of heat in communication with the lower beds of the 
glacial sea. In the Arctic basin the clouds, the melted snow, and 
the great rivers, which have their mouths on the north of both con- 
tinents, produce considerable quantities of fresh water, which, mixing 
