178 Dr. Marcet, on the specific gravity and temperature 
been favoured with many of those specimens, I have not 
been able to obtain results sufficiently conclusive to enable me 
to form a decided opinion upon the subject. On referring to 
the annexed tables, it will be observed, that, in a variety of 
instances, the water at the surface was much lighter than 
when procured from some depth ; but then it would appear 
that whenever such a result was obtained, it was owing to the 
water at the surface being diluted by the melting of large 
masses of ice ; for under ordinary circumstances (as in the 
case marked No. 5, Table I.), no such difference was obtained 
between waters taken at the surface, or brought up from a 
considerable depth ; and in no instance did the density of the 
water of the Atlantic, from whatever depth it was obtained, 
appear to exceed the mean density of the waters of the ocean. 
The fact however may be, and actually appears to be 
different in the case of particular seas or arms of the ocean, 
in which the influence of currents and other local circum- 
stances is more sensibly felt, and the waters of which do not, 
for obvious reasons, necessarily partake of the uniform salt- 
ness of the ocean. The experiment, as was before observed, 
does not appear to have yet been fairly tried in the Mediter- 
ranean, and indeed from the great depth of that sea, it must 
be extremely difficult, if not impracticable, to raise water from 
the bottom, at least at any considerable distance from the coast. 
In the instance of the sea of Marmora, in which water was 
obtained with certainty from the bottom, by means of my 
machine* (Table IV. Specim. 52 to 55), the result was very 
* It was through the kindness of the British Ambassador at Constantinople, Sir 
Robert Liston, that these specimens were procured. Sir Robert has since told me 
that the use of the machine was not attended with the least difficulty. 
