304 THE DEPTHS OF THE SEA. [cHaP. VII. 
There can be no doubt that this view, which of 
late years has received almost universal acceptance, 
is entirely erroneous. It has been shown by M. 
Despretz,' as the result of a series of carefully con- 
ducted experiments which have since been frequently 
repeated and verified, that sea-water, as a saline 
solution, contracts and increases steadily in density 
down to its freezing-poiut, which is, when kept 
perfectly still, about — 3°67 C. (25°4 F.), and when 
agitated — 2°55 C. 
The temperature observations of Sir James Clarke 
Ross during his Antarctic voyage in 1840-41, 
seemed to give support to the theory of a constant 
temperature of 4°°5 C. for deep water, but these obser- 
vations have as evidently been made with unguarded 
instruments, as those of Sir John Ross in 1818 with 
instruments defended from pressure; and although 
I believe they must be taken as proving that in 
high southern latitudes the surface temperature is 
sometimes lower than the temperature of the water 
at a considerable depth beneath, still the amount of 
correction for pressure is uncertain, depending upon 
the construction of the thermometers used, and in 
any case it must reduce the difference considerably. 
A large number of thermometers of the ordinary 
Hydrographic Office pattern were sent out with us, 
as I have already mentioned, in the ‘ Lightning,’ 
and these were of course the instruments used by 
Staff-Commander May for his temperature obser- 
vations. There was an opportunity of testing these 
thermometers, however, on the return of the vessel, 
1 Recherches sur le Maximum de Densité des Dissolutions aqueuses. 
Loc. cit. 
