28 o 
Dr. Davy’s observations on the 
variations of specific gravity observed, do not regularly con- 
form to the difference of temperature. 
That the specific gravity of the water of the ocean, in all 
its parts, however remote, should be nearly the same, is easily 
explained ; it is indeed what might be expected from theory. 
It is more difficult, it appears to me, to account for the slight 
variations ; I may remark, they appeared to me greatest when 
the sea was rough and agitated ; and once the specific gra- 
vity of the water seemed diminished by a heavy fall of rain, 
viz. in lat. 4 0 north, and in long. 18 0 13" west, where we 
experienced a quick succession of tropical squalls. 
Whether there is a specific gravity peculiar to the water of 
each zone, as a modern traveller of high authority endeavours 
to prove, I am greatly in doubt. From my own experiments, 
in which I cannot but put some reliance, I feel much in- 
clined to infer the contrary, and especially from those made 
on land, which I know to be perfectly accurate. Several of 
these agree in giving the same specific gravity to specimens 
of water taken from parts cf the ocean very remote from each 
other; for instance, the water from Jat. o° 12" south, and 
22 0 3 6" south, and that from 34,° 25" south, and the water 
that washes the shores of Colombo. 
For ascertaining the temperature of the air and of the 
water of the ocean, I used delicate pocket-thermometers, the 
bulbs of which projected about an inch from the ivory scale. 
In the experiments on the temperature of the ocean, the water 
was tried the instant it was drawn, before it was affected by 
the air. To find the temperature of the air, I always chose 
the coolest part of the ship on deck, and always put the in- 
