Dr Horner on the Specific Gravity of Sea-Water, 163 
the surface^ their extent over waters of the ocean remote from 
each other, and probably, also, their accuracy, give them a de- 
cided claim to the attention of the natural philosopher ; and 
the perseverance with which they were continued, under various 
circumstances, does honour as well to the Naturalist of the Ex- 
pedition, as to the commander, who not only in calms, but in 
some periods, almost daily, afforded the necessary assistance. 
They were all made with Six’s Thermometer, which is a 
good assurance of their accuracy. It is certainly remarkable, 
that an instrument so simple, so convenient in the use, so cer- 
tain in the results, and which has been long known, is not more 
frequently used for this purpose ; so that in the latest scientific 
voyages, much more uncertain thermometers have been used, 
to which only the deep sea clamm of Captain Ross forms an 
exception. 
Our observations fall under two heads : measurements of the 
temperature in different depths, in the same places of the ocean, 
and in statements of the warmth in the usual soundings, from 
sixty to eighty fathoms, in different places. 
The most complete observations on the changes of the tem- 
perature, in increasing depths, are, in the South Sea, of the 
13th and 14th of September 1817, in 36° north latitude, and 
148° west longitude. Besides confirming the general law, that 
the cold increases with the depth, they also afford the follow- 
ing results. 
1. The upper parts of the water show a particular warmth, 
as the temperature, in the first eight fathoms, diminished only 
0°,4 R., but from that depth to twenty-five fathoms, full 6° R. 
From twenty-five fathoms to a hundred fathoms’ depth the de- 
crease of warmth is considerably less, since, in the next twenty- 
five fathoms, it is only 1°,7 R., and in the next fifty fathoms, 
only l°,5 R. ; a decrease which amounts to only the tenth 
part of the preceding. It is still slower between a hundred 
and three hundred fathoms. 
If we compare these observations with those of the 6th of 
June 1816, in 37° north, and in 199° west longitude, conse- 
quently, in the same parallel of- latitude, the influence of the 
season is particularly observable in the temperature on the 
surface, which in June is 13° R., in September 18" R. It, 
I. 2 
