CHAPTER m 



The Température of the Sea. 



The accurate détermination of the température of the sea, not 

 (»nly at the surface, but at varying depths, is one of the chief 

 concerns of oceanographers. 



A combination of readings of température and salinity 

 enables us to détermine the movements of large masses of 

 océan water and in many instances to détermine the extent, 

 distribution, and boundaries of océan currents. 



Observation of surface températures is an easy matter, since 

 it is only necessary to haul in a bucket of water and read the 

 température rapidly but accurately with.a reliable thermometer. 

 Of course, even hère certain elementary précautions are 

 necessary. 



For readings at intermediate depths spécial apparatus is 

 necessary. The Pettersson-Nansen water-bottle (see p. 103) 

 coUects and insulates water samples from any required depth, 

 and within limits gives an accurate reading of the température 

 of the water samples. 



In the Challenger expédition a maximum and minimum 

 thermometer of the Miller-Casella type was used. At the top 

 of the instrument there are two glass bulbs connected by a bent 

 tube, the left-hand bulb being tilled with créosote, the capillary 

 tube containing mercury, the right-hand bulb having a vacuum 

 except for a little créosote. 



When the thermometer is heated the créosote in the left 

 bulb expands and pushes the mercury through the tube, and 

 with it a small index which sticks at the place where the 

 mercury leaves it. When the thermometer cools the créosote 

 contracts, and the créosote vapours on the right drive the 



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