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, 1 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. (25-4E.), and when 

 agitated -2'55 0. 



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 wal 

 at a considerable depth beneath, still the amount oi 

 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 or din* 

 Hydrographic Office pattern were sent out with us 

 as I have already mentioned, in the 'Lightning, 

 and these were of course the instruments used b; 

 Staff-Commander May for his temperature obser- 

 vations. There was an opportunity of testing thes 

 thermometers, however, on the return of the vessel. 



Recherches sur le Maximum de Densitc des Dissolutions aquei 

 Loe. cit. 



