MR. J. PRESTWICH ON SUBMARINE TEMPERATURES. 
629 
“ 1. The diminution (pointed out) of temperature everywhere up to latitude 60° with 
the increase of depth, in direct opposition to the conditions observed on dry land. 
“ 2. My numerous determinations of the salinity of the ocean have shown that the 
maximum of the salinity does not occur at the equator, but invariably some degrees 
north and south from it (in the Atlantic at 23° N. and 17° S.). I have endeavoured to 
explain this condition from the greater evaporation in these latitudes, which is compre- 
hensible from the cooperation of the trade-wind, in opposition to the region of calms at 
the equator (see Mem. de lAcad. Sc. Math. Ph. et Nat. t. i. p. 507). According to the 
above, I do not, however, doubt that also the slight salinity of the uprising polar water 
in the region of calms contributes materially to this condition. 
“ 3. It is a point which has been determined by Humboldt, John Davy, and others, 
that the water of the ocean is colder at the surface over shallows than at some distance 
from them over very great depths. This phenomenon, the explanation of which hitherto 
has not been found to be satisfactory (Gehler’s New Lexicon, t. vi. 3. p. 1687), is a 
simple consequence of the current of colder water at depths from the pole to the 
equator ; for if this runs against any obstruction, such as a shallow would present, it 
will rise along it as upon an inclined plane, and approach nearer the surface, and in 
this manner the surface will be cooled down.” 
A little later Pouillet*, who does not, however, seem to have been aware of Lenz’s 
researches, remarks : — “ It seems certain that there is in general a surface-current 
carrying towards the polar seas the warm water of the tropics, and a lower current 
bringing back from the poles the cold water of the polar regions ; but these currents 
are modified in their direction and intensity by a number of causes which depend on the 
depth of the sea-basins, their configuration, and the influence of winds and tides.” 
I have already referred to Biot’s criticism of Boss’s work. Beasoning afterwards on 
the different temperatures shown to exist throughout all seas, and on the impossibility, 
in consequence, of any portion of it being in a state of rest, he observes f : — “ The exist- 
ence and the initial direction of these constant currents presupposes three things : first, 
a permanent cause of movement which forces the polar waters towards the equator ; 
secondly, a constant exterior afflux supplying the great polar streams at the origin and 
along their course ; and lastly, some exhausting cause or outflow, preventing the final 
accumulation of their products ” (p. 79). Biot, however, in consequence, apparently, of 
the doubts he felt respecting the accuracy of temperature observations at depths, owing 
to the anomalous results of Boss’s, hesitates to admit “ the inference that the bottom of 
the sea was occupied by a layer of cold water proceeding from the poles and which is 
unceasingly renewed” (p. 71), and attaches more weight as a cause of this circulation 
to the inequality of mean pressure of the atmosphere in different latitudes. 
Buff J gave in 1850 a good general summary of the question as it then stood. 
* Elements de Physique, 5 ed. vol. ii. p. 666 (1847). 
t * Journal des Savans ’ for 1849. 
t ‘ Physics of the Earth,’ translated by Hofmann. London, 1851, pp. 172-74. 
4 p 2 
