accepted as if they were ascertained facts. Of course, if sea-water, like
fresh water, were heaviest at a temperature of 39° F. and got lighter as
it approached 32° F., the water of the bottom of the deep sea could not
be colder than 39°. But one of the first results of the careful
ascertainment of the temperature at different depths, by means of
thermometers specially contrived for the avoidance of the errors produced
by pressure, was the proof that, below 1000 fathoms in the Atlantic, down
to the greatest depths yet sounded, the water has a temperature always
lower than 38° Fahr., whatever be the temperature of the water at the
surface. And that this low temperature of the deepest water is probably
the universal rule for the depths of the open ocean is shown, among
others, by Captain Chimmo's recent observations in the Indian ocean,
between Ceylon and Sumatra, where, the surface water ranging from 85°-81°
Fahr., the temperature at the bottom, at a depth of 2270 to 2656 fathoms,
was only from 34° to 32° Fahr.

As the mean temperature of the superficial layer of the crust of the
earth may be taken at about 50° Fahr., it follows that the bottom layer
of the deep sea in temperate and hot latitudes, is, on the average, much
colder than either of the bodies with which it is in contact; for the
temperature of the earth is constant, while that of the air rarely falls
so low as that of the bottom water in the latitudes in question; and even
when it does, has time to affect only a comparatively thin stratum of the
surface water before the return of warm weather.

How does this apparently anomalous state of things come about? If we
suppose the globe to be covered with a universal ocean, it can hardly be
doubted that the cold of the regions towards the poles must tend to cause
the superficial water of those regions to contract and become
specifically heavier. Under these circumstances, it would have no