THE HAUNTS OF LIFE 85 



side of a whalebone whale's skeleton preserved in the 

 Museum of Monaco may be a record of the animal's having 

 gone beyond the limit of safety. He recalls Paul Bert's 

 experiment, in which the pressure of the air in the lungs of 

 a dog was reduced by a not very large fraction of an atmo- 

 sphere, with the result that the thorax collapsed with 

 every rib broken. 



(3) Temperature. The sun's heat is lost at about 150 

 fathoms, and the Deep Sea is therefore intensely cold. 

 With relatively little variation (2 or 3 Fahr.) in the year, 

 the temperature remains near the freezing point of fresh- 

 water (32 Fahr.). The bottom temperature may be below 

 30 Fahr. in Polar waters, and over 90 per cent, of the whole 

 sea-floor it may be said that an eternal winter reigns. 

 What a contrast this is to the surface conditions, which 

 may show an annual variation of 50 in one area, and which 

 show such extremes as 26 Fahr. off Nova Scotia and 96 in 

 the Persian Gulf ! The variations and extremes on land 

 are still more marked. 



The coldness of the deep water seems to be mainly due 

 to a flow of cold bottom-water from the Southern and 

 Antarctic oceans towards the equator, and in a less degree 

 to a similar flow from the sub- Arctic region. The causes 

 of this flow are complex, but the oceanographers refer to 

 the great intertropical evaporation, to the action of extra- 

 tropical winds which blow the surface-waters polewards, 

 to ' the head of water ' which is accumulated in high lati- 

 tudes by the action of the prevailing winds, and to the 

 greater density of the water in high latitudes. As temper- 

 ature affects the solubility of gases in water, cold water 

 being able to absorb more than warm water, the polar 

 waters contain more oxygen than elsewhere, and the 



