AA On the Depth and Saltness of the Ocean. 
iments, the zone of mean temperature lies between the — 
of 54° and 60° of south lat., not only at the surface, but to 
great a depth as the ocean has been penetrated. Pature trials nr 
the northern hemisphere remains yet to be uinvorehicatt This 
mean temperature is met with both within the polar circles and 
in proceeding towards the equator. In the higher latitudes above 
60°, the ocean in descending increases in temperature until it ar- 
rives at its mean point; while proceeding towards the equator it 
ases from the surface downwards; this decrease beyond the 
tropical circle, is about twenty-three fathoms for every degree of 
latitude. Within the tropics it is 1° for every thirteen fathoms a 
of depth. until 400 fathoms, after which it ap a descent of ¥ 
from 200 to 300 fathoms to effect a like chan 
From the observations of Admiral DUrville, it would appear 
that the waters of the Mediterranean do not follow the rate of 
descent of the Atlantic and Pacific Oceans. He estimated the 
mean temperature of that sea below 200 fathoms, at 55°, and 
this from the fact of his having obtained that temperature at the 
depth of 1000 fathoms. If this be so, it leads to-an interest- 
ing enquiry, as to whether it may not be in consequence of an 
vast internal fires that are known to prevail in ont beanie ee that 
surround it. Hee 
The penetrations of solar light or the depth at wie it be- 
comes totally absorbed, is another subject which claimed 
lar attention during the cruise of the Exploring Expedition. The 
mode of obtaining “results was to let down a pot, bottom upwards, 
painted white, some eighteen inches in diameter, by the deep 
sea line until it was lost sight of, noting the depth at which it 
disappeared, and then again its reappearance, the mean being 
taken for the result; these seldom differed more than a fathom; 
the eye was placed five feet above the surface in the direction 
with the line by which the pot was held. he would appear at 
first that the depth at which an object could be seen would de- 
pend upon the intensity as well as the soa at oe the rays of 
light fell upon the surface of the ocean. ‘They undoubtedly have 
some effect, but seldom made a greater dilicresen’ than 14 fath- 
oms. Under different latitudes and in different temperatures of 
— water, the anomalies far exceeded this, and were indeed too 
in 1 the keen of the waters, affected in a great degree t 
| ssion of the rays of light, or their absorption. — In water | 
: at the temperature of 78° to 80°, the white object described was 
iscernible at a depth of 180 feet, while in water at 36°. ‘it was : 
oa ne of at 40 0 feet. cain. > ct ee ntil 
