28 
THE OCEAN WORLD. 
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 occa- 
sioned 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 four degrees below 
zero, would produce the most singular consequences. As its tempera- 
ture 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 four degrees 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 two decrees 
below zero. By evaporation at the surface it is concentrated and°pre- 
cipitated, 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 prepares the grand horizon- 
tal current which puts these submarine reservoirs of heat in com- 
munication 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 continents, produce considerable 
quantities of fresh water, which, mixing with the waves of the Polar 
