4. Reversing thermometer 



Nearly all observations of sea water temperatures below 900 

 feet have been made with reversing thermometers. First introduced 

 in 1874, the reversing thermometer remains today the most reliable 

 and accurate means of measuring sea temperatures, particularly 

 deep ocean temperatures. Also, the differences between the corrected 

 temperature values from paired protected and unprotected reversing 

 thermometers will indicate the depths of the observations. Good revers- 

 ing thermometers can give temperature to ±0.02°C and depth to ± 0.5 

 percent ui the actual value. (A Japanese scientist has built a reversing 

 thermometer accurate to ±0.005°C.) 



However, reversing thermometers give temperature information 

 from discrete depths or points instead of the more desirable continuous 

 record; interpolation often is necessary for comparison of temperatures 

 at standard depths. Nor can reversing thermometers provide an 

 instantaneous record; when the thermometers are back on deck they 

 are read, and the readings are recorded and corrected to obtain the 

 in situ temperature. Reversing thermometers must be calibrated 

 periodically or whenever there is reason to suspect their accuracy. 

 The calibration equipment is also rather elaborate if the pressure 

 factor is to be taken into account. 



5. Other devices 



Oceanographic institutions and laboratories all have at some 

 time or other designed and built one or more different types of electric 

 or electronic temperature-depth measuring devices. However, no single 

 device has withstood the test of time to the extent that it has been 

 generally adopted and used by others. In fact, most of these devices 

 have been discarded by the laboratories of their origin. Two systems 

 recently have shown promise and are discussed in greater detail below. 



Greater success has been achieved in the continuous measurement 

 and recording of sea surface temperatures than in measurement of 

 temperatures at depth because the absence of the pressure factor has 

 made the solution much easier. Surface "thermitows" have been devised 

 that consist essentially of a sensitive resistance thermometer coupled 

 to an automatic recorder. The main difficulty of this system at present 

 is the processing of literally miles of sea surface temperature records 

 that are obtained with this equipment. 



Ill -5 



