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. ia 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 prevaihng winds, and to the 

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

 ature affects the solubiUty of gases in water, cold water 

 being able to absorb more than warm water, the polar 

 waters contain more oxygen than elsewhere, and the 



