CHAPTER III 



THE TEMPERATURE OF THE SEA. 



THE accurate determination of the temperature of the sea, not 

 only at the surface, but at varying depths, is one of the chief 

 concerns of oceanographers. 



A combination of readings of temperature and salinity 

 enables us to determine the movements of large masses of 

 ocean water and in manv instances to determine the extent, 

 distribution, and boundaries of ocean currents. 



Observation of surface temperatures is an easy matter, since 

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

 temperature rapidly but accumtely with a reliable thermometer. 

 Of course, even here certain elementary precautions are 

 necessary. 



For readings at intermediate depths special apparatus is 

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

 collects and insulates water samples from any required depth, 

 and within limits gives an accurate reading of the temperature 

 of the water samples. 



In the Challenger expedition 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 filled with creosote, the capillary 

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

 except for a little creosote. 



When the thermometer is heated the creosote 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 creosote 

 contracts, and the creosote vapours on the right drive the 



47 



