NEED FOR OBSERVATIONS 27 



simultaneously. Work of this kind attains its highest 

 development in such special organizations as those of 

 the International Committee for the Study of the 

 Sea, or the combined Antarctic expeditions ; but much 

 useful work can be done by ships cruising in areas 

 outside the field covered by these organizations, as 

 in the expeditions of Dr. Wolfenden's " Walwin " and 

 '.' Silver Belle," or in almost any region, by ships taking 

 regular routine observations of a more or less elaborate 

 character, and communicating the results to a central 

 authority, such as the Meteorological Office, for 

 collation with the records of other observers. As 

 examples of what may be done in this way from 

 surface observation alone, reference may be made to 

 the surface temperature charts published officially in 

 this country, the United States, and elsewhere, and 

 the surface salinity map which illustrates this chapter. 

 All these depend on the daily observations made on 

 board liners, tramps, whalers, yachts, and ocean- 

 faring craft of all descriptions. 



The second fundamental fact is, that in all oceans 

 the conditions below a certain depth are very uniform 

 over a considerable horizontal and vertical range, and 

 changes take place with great slowness if they occur 

 at all. Now, observations in the depth must be made 

 from vessels of considerable size, and with somewhat 

 elaborate and expensive equipment ; but the minimum 

 tonnage is well below that common amongst ocean- 

 going steam-yachts, and the cost of the necessary 

 equipment is not of an order of magnitude greater 

 than other outfits in such vessels. And the conditions 

 just explained make observations of this kind valuable, 

 wherever and whenever they are made ; for the great 

 lines of soundings laid down by the deep-sea ex- 

 peditions and the cable ships are separated by vast 



