Reversing Thermometers 



constricted part 

 of the capillary 

 in a set position 

 and in a reversed 

 position 



To record temperature at any depth 

 three thermometers are attached 

 to a water sampling bottle (right) 

 which closes, and reverses the ther- 

 mometers, as required (page 210). 

 When each protected thermometer 

 is reversed (left), the mercury 

 column breaks at the constriction 

 between the large reservoir and the 

 loop and runs down into the bulb 

 and part of the graduated capillary. 

 The loop traps any mercury forced 

 past the constriction when the tem- 

 perature rises after reversal. An 

 auxiliary thermometer mounted along- 

 side is used to correct for the 

 effect of temperature change 

 between the time of reversal and the 

 time of reading. The thermometer 

 is protected by being enclosed in a 

 strong glass tube, of which the part 

 around the reservoir is filled with 

 mercury to help conduct heat. The 



reading of the unprotected reversing 

 thermometer, which has no strong 

 glass sheath, is increased by the 

 pressure, but this is not so with 

 the protected thermometer; so the 

 difference between the readings of 

 the two types, mounted and reversing 

 together, can be used to determine 

 the depth of reversal, 



protected unprotected 



reversing reversing 



thermometer thermonneter 



Thermostat Salinity Meter 



Developed by R. A. Cox, this meter 

 measures the salinity of sea water to 

 an accuracy of one part in 10,000. 

 It operates on the principle that 

 electrical conductivity is proportional 

 to salinity. The salinity of a 

 sample of sea water is found by com- 

 paring its conductivity with that of 

 "standard" sea water. To minimize 

 temperature effects both samples of 

 water are placed in the same thermo- 

 stat bath (center in photo above). 



Current Meters 



The Ekman current meter shown above 

 consists of three main components: 

 1. a vane which orients the instrument 

 so that it is kept heading into 



the current; 2. a propeller, the 

 revolutions of which are recorded on 

 a dial and measure the current's 

 speed; 3. a special compass that 

 reveals the current's direction. The 

 modified Roberts current meter (at 

 left) has propellers to measure 

 speed, a magnetic compass to measure 

 direction, and a pressure gauge to 

 measure depth. Readings are sent 

 to the ship electrically through 

 the wire holding the current meter. 



257 



