TEMPERATURE AND MOVEMENTS OF THE DEEP SEA. 
131 
or sometimes as low as 60 degrees. Then a further loss of tem- 
perature would be experienced in going down to 100 fathoms. 
At that depth we came almost invariably to 54 or 55 degrees; 
and whatever was the temperature at 100 fathoms, that it was 
down to the very bottom ; depth there made no difference at 
all ; if it was 55 degrees at 100 fathoms it would be 55 at 1,700 
fathoms; and if it was 56 degrees at 100 fathoms it would be 
the same at the greatest depth. There was a little difference 
in different parts of the area, which can be explained by local 
causes; but, as a rule, whatever the temperature was at 100 
fathoms, that it was at the bottom. 
Now what is the cause of this difference between the Medi- 
terranean and the Atlantic ? In a basin of very great depth, 
like the Mediterranean, why should the temperature be thus 
curiously uniform ? Simply because it is entirely cut off from 
this General Oceanic Circulation, so that the water takes the 
temperature of the crust of the earth at that particular part. I 
will give you some curious evidence that such is the case. 
Thermometers buried deep in the soil in Central Europe are 
found to vary very little indeed during the different seasons. 
At about 20 or 30 feet from the surface they are not deep 
enough to be influenced by what is called the “ internal heat 
of the earth,” which you experience when you go down into a 
deep coal-pit, for instance, or which shows itself in the hot 
water from very deep springs ; and at that depth they are 
covered with a layer of earth which is a sufficiently bad con- 
ductor to prevent their being much influenced by season 
changes ; they therefore take the 'permanent temperature of 
the crust of the earth, and that permanent temperature in 
Central Europe is found to be about 51, 52, or 53 degrees. Now 
I found that ‘there was a cave in a little island which we visited 
between Sicily and the coast of Africa, which has the reputation 
of being “ icy cold.” I was very anxious to visit it, but circum- 
stances did not allow of our doing so ; however, I had afterwards 
the opportunity of learning that the temperature of this cave is 
54° through the whole year. Then a Maltese gentleman, the 
collector of customs at Yaletta, a very intelligent and well- 
informed man, told me that it is the practice among the natives 
to let down their wine to cool it in the deep tanks which they 
have excavated in the rock. I asked him if he happened to 
know the temperature in these deep tanks, and he said, “ Yes, 
it is 54 degrees.” So you see we have several pieces of confirm- 
atory evidence, showing us that the bottom-water of the Medi- 
terranean takes exactly the temperature of the crust of the earth 
on which it rests. 
If, then, it were not for the vertical circulation of the water 
in our great Oceanic basins, the temperature of the bottom 
