with the water and is subject to hydrostatic 

 pressure. It has no mercury surrounding the 

 reservoir as does the protected thermometer. 

 Since the thermometer is subject to hydrostatic 

 pressure, it does not give a true temperature 

 reading but gives a reading which increases ap- 

 proximately 1° C. for each 100 meters of depth. 

 The unprotected thermometer, when used with 

 a protected thermometer, is a pressure gage for 

 determining the exact depth of the Nansen 

 bottle at the time of reversal. By pairing a 

 protected and an unprotected thermometer, 

 temperature and temperature-pressure are ob- 

 tained in situ. The water temperature is 

 determined by correcting the readings of the 

 protected thermometer. Corrections for the 

 unprotected thermometer must also be applied. 

 The diflference between the two readings is used 

 to compute the actual depth of the Nansen 

 bottle at the time of reversal. The methods 

 for carrying out these computations are given 

 in chapter 3. 



2-22 Arrangement of Reversing Thermom- 

 eters on the Nansen Bottles. — Because the 

 methods for computing the depths of the Nan- 

 sen bottles require that the readings for the 

 protected thermometers be corrected before 

 those of the unprotected, it is customary to 

 place the protected thermometers in the left- 

 hand tube of the thermometer frame and the 

 unprotected in the right-hand tube. This 

 enables the reading of the thermometers and 

 recording of the data on the log sheet in the 

 proper order for applying the corrections. 

 Thus, errors in computations are reduced (fig. 

 2-7). 



It usually is not necessary to place unpro- 

 tected thermometers on every Nansen bottle 

 to be used in a cast. They should be placed 

 strategically so that the depths of reversal of 

 other bottles in the cast can be readily inter- 

 polated. A protected thermometer generally 

 is substituted for the omitted unprotected. 

 The corrected readings of the two protecteds are 

 averaged to determine the temperature in situ. 



On shallow casts, i. e., those commencing 

 with bottles at the surface, it is best to group 

 the unprotected thermometers on the lower 

 bottles, as this type thermometer will not 

 record accurately at shallow depths. 



On deep casts, i. e., those commencing at 

 depths below those of the shallow casts, it is 

 important that unprotected thermometers be 

 placed on the top and bottom bottles. The 

 remaining unprotected thermometers should be 

 spaced at as nearly equal distances along the 

 wire as possible. 



14 



r 



Figure 2-7. View of reversing therinometers on a 

 Nansen bottle. 



H. O. 607 



