II THE PROBLEMS OF THE DEEP SEA 61 



Porcupine in their cruises of 1868 and subsequent 

 years. 



But biology, in the long run, rests upon physics, 

 and the first condition for arriving at a sound 

 theory of distribution in the deep sea, is the 

 precise ascertainment of the conditions of life; 

 or, in other words, a full knowledge of all those 

 phenomena which are embraced under the head 

 of the Physical Geography of the Ocean. 



Excellent work has already been done in this 

 direction, chiefly under the superintendence of Dr. 

 Carpenter, by the Lightning and the Porcupine* 

 and some data of fundamental importance to the 

 physical geography of the sea have been fixed 

 beyond a doubt. 



Thus, though it is true that sea-water steadily 

 contracts as it cools down to its freezing point, 

 instead of expanding before it reaches its freezing 

 point as fresh water does, the truth has been 

 steadily ignored by even the highest authorities 

 in physical geography, and the erroneous con- 

 clusions deduced from their erroneous premises 

 have been widely accepted as if they were 

 ascertained facts. Of course, if sea-water, like 

 fresh water, were heaviest at a temperature of 

 39 F. and got lighter as it approached 32 F., 

 the water of the bottom of the deep sea could not 

 be colder than 39. But one of the first results 

 of the careful ascertainment of the temperature 

 1 Proceedings of the Royal Society, 1870 arid 1872 



