104 Temperature Sections Surveyed. 



isotherms appear almost at the same level from one end of the 

 section to the other in the diagram of Plate 15, the distribution 

 of temperature varies from one station to another. There is a 

 gradual decrease of temperature between ioo fathoms and 500 

 fathoms as we proceed westwards until we arrive at Station 182, 

 which is the coldest, after which the temperatures rise again 

 towards Station 184. The warm surface-stratum above 25 C. 

 is only 10 fathoms deep between the Fiji Islands and the New 

 Hebrides at Stations 175 and 176, a decrease probably due to 

 the influence of a cold current from the southward, perhaps a 

 branch of the cold current flowing northwards along the west 

 coast of New Zealand. Its depth rapidly increases as we enter 

 the Melanesian basin at the New Hebrides, attains a maximum 

 of 55 fathoms at Station 179, falls to 25 fathoms at Station 182, 

 and increases again to 40 and 45 fathoms as we approach Torres 

 Strait. These alterations of level, which represent a difference 

 in the thickness of the warm surface-stratum of over 100 feet, 

 must be caused by warm and cold surface-currents flowing into 

 the basin from the north or south. 



Sections from Torres Strait to Hong-kong, and from 

 Hong-kong to the Admiralty Islands (Plate 16, Table X.). — 

 These sections embrace the numerous seas between Papua and 

 China, and are chiefly interesting as offering several instances of 

 the influence of submarine and surface barriers upon the dis- 

 tribution of temperature, the former interfering with the gradual 

 decrease of temperature between the surface and the bottom, the 

 latter resulting in a superheating of the surface-strata, which 

 in these seas, as well as in others similarly circumstanced, attain 

 a temperature not observed in the open ocean. 



The Arafura Sea.— Following the track of H.M.S. " Chal- 

 lenger," we enter the Arafura Sea through Torres Strait. The 

 soundings taken between the latter and the Arrou Islands prove 

 that the continents of Australia and Papua are bound together 



