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-point, which is, when kept 

 perfectly still, about -3°-67 C. (25°-4P.), and when 

 agitated -2°-55 0. 



The temperature observations of Sir James Clarke 

 E,oss during his Antarctic voyage in 1840-41, 

 seemed to give support to the theory of a constant 

 temperature of 4°'5 0. for deep water, but these obser- 

 vations have as evidently been made with unguarded 

 instruments, as those of Sir John E-oss 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 OfB.ce 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, 



' Recherches sur le Maximum de Density des Dissolutions aqueusea. 

 Log. cit. 



