616 
ME. J. PRESTWICH ON SUBMARINE TEMPERATIJEES. 
contrary, sea-water gradually increased in weight down to the freezing-point, until it 
actually congealed.” Other experiments led him to fix this point of greatest density at 
22° F. 
Erman* in 1828 fixed the maximum density of sea-water of 1*027 specific gravity at 
25° F., and found likewise that it did not reach its maximum before congelation. Still 
more conclusive were the more elaborate experiments of Despretz j* in 1837. Taking 
distilled water at a temperature of 20° C. and sea-water of the specific gravity of 1*027 
at 20° C., he successfully determined the following important points : — 
Cent. Eahe. 
O O 
Maximum density of freshwater +1 =39*2 
,, sea-water —3*67=25*4 
Point of congelation of sea-water —2*55=27*4 
Temperature of sea-water during congelation . . . —1*88=28*6 
He also showed that the freezing-point and the point of maximum density were pro- 
portionate to the quantity of saline matter in the water, and that both therefore varied 
with the degree of salinity of the sea. 
The effects of pressure and the properties of fresh and salt water were therefore per- 
fectly well understood previous to the date of Ross’s voyage. How, then, the unsup- 
ported opinion of one who, though a most able and enterprising navigator, had not any 
pretensions to an exact knowledge of physical science could have been accepted by 
scientific writers of so much eminence is a singular fact. I can only account for it by 
the circumstance that the subject had not been made in this country one of special 
investigation, and therefore the results of Ross’s work had not been questioned by any 
competent special authority. In fact they had never been discussed. 
The observations of Leez, Hu Petit-Thouaes, and others, combined with the 
researches of physicists, had sufiiciently established the law of the decrease of tempe- 
rature with the depth to 2° to 3° above the zero of Centigrade in the temperate and 
tropical zones of both the great oceans ; and their conclusions could hardly be consi- 
dered as seriously affected by the unsupported though ingenious hypothesis of D’Urville 
and Ross. Lenz had obtained, by means of his bathometer, with corrections for change 
of medium, the low readings given at p. 599 ; and subsequently Du Petit-Thouars by 
means of protected thermometers had obtained directly, without correction J, amongst 
a number of others at lesser depths, the following deep-sea temperatures : — 
* “ Nouvelles Recherches sur le maximum de densite de l’eau salee,” Annales de Chimie, xxxviii. p. 287. 
•f* “ Recherches sur le maximum de densite de l’eau pure et des dissolutions aqueuses,” ibid. Ixx. p. 5. 
J Others of his observations were corrected. On his return his thermometers were found to give too, high 
a reading by -A to -A of a degree Centigrade, so that his observations may require a further slight deduction 
to this extent. 
