Figure 



Reading the reversing thermometers. 



mometer reader, or viewer. Each thermometer 

 actually consists of two parts: one, the reversing 

 thermometer which is called the main; the other, 

 a regular thermometer which is called the 

 auxiliary (fig. 2-6). 



2-18 The Main Thermometer. — The main 

 thermometer is essentially a double ended ther- 

 mometer. In the upright position, it consists 

 of a large reservoir of mercury at the lower end 

 connected by means of a fine capillary to a small 

 bulb at the upper end. The capillary is con- 

 stricted and branched just above the reservoir. 

 This point is called the appendix. Above the 

 appendix, the thermometer is bent in a 360° 

 loop, called the pigtail, from which it continues 

 straight and terminates with the bulb. The 

 thermometer is so constructed that in the up- 

 right position mercury fills the reservoir, the 

 capillary, and sometimes part of the bulb, de- 

 pending upon the temperature. When the ther- 

 mometer reverses, the mercury column breaks 

 at the appendix, descends into the bulb, now 

 at the bottom, thereby filling the bulb and part 

 of the stem, and thus indicates the temperature 

 at the depth of reversal. The mercury remains 

 at this reading until the thermometer is returned 

 to the upright position when the mercury drains 

 from the bulb and rejoins that in the reservoir. 



2-19 The Auxiliary Thermometer.— The 

 auxiliary thermometer is a small, ordinary mer- 

 curial thermometer that is mounted alongside 

 the main thermometer. It is used to obtain the 

 temperature of the reversing thermometer at 

 the time the main is read. Corrections are 

 applied to the reading of the main for changes 

 resulting from differences between the tempera- 

 ture at reversal and at the time of reading. 



2-20 Protected Reversing Thermometers. — 

 The main and auxiliary thermometers are en- 



H. O. 607 



ENLARGED SECTION SHOW- 

 ING PIGTAIL (A) APPENDIX 

 DEAD ARM (B) AND BREAK- 

 OFF POINT (C). 



■H CD- 



ENLARGED SECTION SHOW- 

 ING READINGS ON MAIN 

 STEM (D) AND AUXILIARY 



-GLASS JACKET 



i 



(IN REVERSED POSITION) ^=^ 



PROTECTED UNPROTECTED 



Figure 2-6. Protected and unprotected deep-sea 

 reversing thermometers. 



closed in a heavy glass jacket. When sealed 

 at both ends and the air within partially evacu- 

 ated, it is called a protected thermometer. The 

 area surrounding the reservoir is filled with 

 mercury, wliicli serves as a thermal conductor 

 and gives greater sensitivity to temperature 

 change. The sealed jacket protects the ther- 

 mometer from hydrostatic pressure thereby giv- 

 ing a true reading of the water temperature in 

 situ. 



2-21 Unprotected Reversing Thermome- 

 ters. — An unprotected reversing thermometer 

 is similar to the protected in that the main and 

 auxiliary thermometers are enclosed in a heavy 

 glass jacket. However, the jacket of the un- 

 protected thermometer is open at one end. 

 The reversing thermometer is in direct contact 



13 



