TEMPERATURE OF THE SEA. 
345 
temperature of the surface being 30°. The instrument having remained at the 
given depth seventeen minutes, and having been drawn up in five minutes and 
a half, the inclosed thermometer marked 34° ; the temperature of the sea 
at the depth of 100 fathoms being four degrees higher than at the surface. 
On December the 23d he repeated the experiment at the same depth, 
the temperature of the air being 33’, of the surface 32°, the instrument 
having remained down sixteen minutes and been withdrawn in six and a 
half, gave a temperature of 34 i° ; in this instance the temperature of the 
sea at the given depth was 21° higher than at the surface. The experiment 
of Irving* is no less at variance with the result of experiments made when 
the surface has been of a comparatively high temperature ; and his experi- 
ment is the more interesting, as his instrument descended below the ice. 
On August the 4th, 1773, when in 80° 30' N. lat., he sent down an appa- 
ratus to the depth of sixty fathoms, the temperature of the air being 32 ? , 
of the surface 36°, and the instrument being drawn up the inclosed ther- 
mometer stood at 39°, the temperature at the given depth being 3° higher 
than that of the surface. 
These facts show the necessity of further experiments before we can 
frame a due expression of the law regarding the temperature of the sea 
at different depths. Observations in various latitudes and various depths 
must be greatly multiplied before it will admit of precise definition. In 
the present state of information on the subject it may perhaps be legitimate 
to conclude, that the temperature of the sea in all latitudes diminishes in 
proportion to its depth within some limit, when the temperature of its surface 
is much above the freezing point. 
I may venture in this place to remark, that the greater temperature of the 
sea near the poles, at considerable depths, than at the surface, favours the 
opinion of the bottom of the ocean being constantly at a uniform tempera- 
ture. What this temperature may be we do not possess sufficient data to 
determine ; but it is not perhaps unreasonable to conjecture (leaving the 
theory of a central fire out of consideration) that it is at that point where the 
water has the greatest density, a point known to be above that of freezing. 
The zealous naturalist of the French expedition to Terra Australis, in 
endeavouring to establish his favourite propositions, that the temperature 
* Phipps’s Voyage. 
