of sea waters, in different parts of the ocean , &c. 187 
trary, it begins to expand, and continues to do so till it be- 
comes solid, at which moment it undergoes a farther and much 
more considerable expansion.* The question which I was 
desirous of ascertaining was, whether the same, or any ana- 
logous law, prevailed in regard to sea water. 
The mode in which I first attempted to decide this point, 
was simply by cooling sea water, by means of cooling mix- 
tures, till it reached the freezing point, and ascertaining its 
specific gravity, at each degree of temperature, as it ap- 
proached congelation. Researches of this description are 
liable to a variety of practical difficulties, which I could not 
altogether overcome by this method, and the results which I 
obtained, offered slight inconsistencies, which prevented my 
relying upon their strict accuracy. -f Still however they uni- 
formly led me to the conclusion, that the law of greatest spe- 
cific density at 40°, did not prevail in the case of sea water ; 
but that, on the contray, sea water gradually increased in 
weight down to the freezing point, until it actually congealed. 
Soon afterwards I used another method, which afforded 
more precise, and, as far as I am able to judge, decisive re- 
sults. Instead of weighing the water, I measured its bulk, 
under various temperatures, by means of an appropriate ap- 
paratus. A sketch of this instrument ( which was executed 
by Mr. Newman) is given in Plate XII., and an explanation is 
annexed, which supersedes the necessity of any farther de- 
* Philosophical Transactions for 1788, page 143. 
f In experiments of this kind it is always necessary to make an allowance for the 
contraction of the glass vessel, the effect of which is to produce an apparent expansion 
of the fluid contained in it. There are formulae for this purpose, and in particular 
that derived from Roy’s experiments, which was adopted in Gilpin’s Tables. Ac- 
cording to Roy, a vessel of glass of the capacity of 10.000.000, would enlarge, by 
1 degree, to the capacity of 10.000.129. 
