36 



The Sea-water and its Physical and Chemical Properties 



Fig. 20. Reversing thermometer (with visible constriction). 



volume of the small bulb and the capillary of the main thermometer until 0°C and 

 expressed in degree units on the capillary scale, 1/6100 = jS being the coefficient of 

 expansion of mercury. The corrections given by the formula are listed in tables to 

 allow quick accurate working (Schumacher, 1923, 1933; Hidaka, 1933; Geissler, 

 1934). Kalle (1953) has given a simple graphical method for the determination of the 

 corrections (C). A calibration correction has to be added to the corrected reading 

 of the thermometer. 



By very careful attention to all the factors involved (continual checking of the re- 

 versing apparatus, accurate readings using a magnifying glass, checking the zero 

 point, proper correction) the mean error in the temperature determination can be 

 kept down to, on the average, ±0-01 °C. This method gives the temperature at single 

 points in the ocean and is of considerable use in series observations at oceanographic 

 stations. For a special purpose, however, it may be desirable to have a continuous 

 record of the temperature at a fixed depth or to obtain quick successive readings of the 

 temperature in a particular layer. A thermograph is usually used for the first purpose 

 (at coastal stations or for continuous recording of the temperature at the surface of 

 the sea from a moving vessel). For greater depths diff'erent types of electrical resistance 

 thermometers have been designed but they have not yet proved very satisfactory in 

 use. For a rapid survey of the upper 150 m of the sea or for a continuous registra- 

 tion of the vertical temperature gradient of this upper layer to about 200 m, Spil- 

 HAUS (1938, 1940) has developed and tested a bathythermograph. This has proved 

 successful and offers considerable advantages where rapid changes of temperature 

 can be expected. For greater depths Mosby (1940) has designed a "thermosounder" 

 that has given useful results. 



3. Salinity and its Determination 



One of the most important properties of water is its ability to dissolve a very large 

 number of solids and gases without chemically reacting with them. As a consequence 



