624 
ME. J. PBESTWICH ON SUBMARINE TEMPEEATUEES. 
on the assumption that the entrance of the deeper polar currents into the Straits 
of Gibraltar, where the water at the surface flows in from the Atlantic Ocean from west 
to east, is hindered by the submarine counter-currents, which move from east to west, 
from the Mediterranean into the Atlantic The zones at which occur the 
maxima of the oceanic temperature and of the density (the saline contents) of its waters 
do not correspond with the equator. The two maxima are separated from one another, 
and the waters of the highest temperature appear to form two nearly parallel lines north 
and south of the geographical equator. Lenz, in his voyage of circumnavigation, found 
in the Pacific the maxima of density in 22° north and 17° south latitude, whilst its 
minimum was situated a few degrees to the south of the equator. In the region of calms 
the solar heat can exercise but little influence on evaporation, because the stratum of air 
impregnated with saline aqueous vapour, which rests on the surface of the sea, remains 
still and unchanged.” 
Similar views were adopted by D’Atjbuisson in 1819*. The whole subject of Oceanic 
circulation was again discussed from a fresh point of view by D’Urville f in his account 
of the results of his voyage of 1826. After arguing (p. 62) that in open seas the tempe- 
rature at and below 600 brasses (3198 feet) is nearly constant between 4° C. and 5° C., and 
that perhaps it may be 4°-4 C. (40° P.), he significantly remarks that in the zone 
10° on each side of the equator some particular cause seems to occasion in the water 
“ up to 100 brasses a more sudden and rapid cooling than would have been expected.” 
He afterwards (p. 64) proceeds to say that the mass of the equatorial waters, slowly 
diminished by evaporation, may give rise to a slow and continuous ascensional movement 
of the lower colder waters, and these so displaced make room for other waters coming 
from the polar regions, so that “ it is rather a transport, nearly in mass and very slow, of 
the deep waters of high latitudes towards the equator.” The point of departure he con- 
sidered to be between 40° and 60° lat. ; and he inferred that the deep cold waters (at 
40°) are there directed periodically in two “ insensible currents,” the one towards the 
equator and the other towards the pole. 
AragoJ in 1838, reporting to the French Institute on a scientific expedition then in 
course of preparation to the coast of Africa, thus expresses his opinion : — 
“ La temperature des couches inferieures de l’ocean, entre les tropiques, est de 22° a 
25° centigrades au-dessous du plus bas point auquel les navigateurs aient observe le ther- 
mometre a la surface. Ainsi, cette couche si froide du fond n’est point alimentee par la 
precipitation des couches superficielles. II semble done impossible de ne pas admettre 
que des courants sous-marins transportent les eaux des mers glaciales j usque sous 
l’equateur. 
* Traite de Geognosie (Strasbourg, 1819), p. 450. 
t ‘ Yoyage de 1’ Astrolabe, 5 Sect. Meteorologie, Physique, et Hydrographie, chap. iii. pp. 51 *-85*. Paris, 
1833. 
t “Instructions concernant la Me'teorologie et la Physique du Globe, par M. Arago, Courants Sous-marins,” 
Comptes Eendus, 1838, part 2, tome vii. pp. 212, 213. 
