CHAPTER II 

 THE WATER 



BY H. N. DICKSON AND D. J. MATTHEWS.* 



OUR knowledge of the physical geography of the sea, 

 of its depths, the composition and physical conditions 

 of its waters, and their movements, is wholly derived 

 from observations made from the surface. Surface 

 conditions themselves can of course be observed 

 directly from on board ship. Observations in the 

 depth must be made indirectly i.e., by means of 

 instruments, which can be sent to the point at which 

 it is desired to make an observation and caused to 

 record a condition there, or to bring back a sample 

 from which the condition may be inferred. 



The work of the earlier deep-sea expeditions, such 

 as those of the " Challenger/' brought two funda- 

 mental facts to light. It became clear first that the 

 conditions in some regions of the sea vary within 

 certain fairly narrow limits. Some of these variations 

 are periodic, some non-periodic, but a knowledge of 

 their range from season to season and from year to 

 year is of the highest scientific and economic im- 

 portance. Such knowledge is gained by repeated 

 observations from large numbers of vessels, distributed 

 over a wide area, and observing as far as possible 



* Of the joint writers of this chapter, Dr. Dickson has con- 

 tributed the more theoretical part, Mr. Matthews the practical 

 section. ED. 



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