which the thermometer is made. 

 The X- value is given on the cahbra- 

 tion sheet. 

 An example of correcting an unprotected 

 thermometer is shown as f oUows : 

 Given : 

 7"„= 16.40° C. (Uncorrected main ther- 

 mometer as shown on the A-sheet. 

 <'b=20.7° C. (Uncorrected auxiliary ther- 

 mometer as shown on the A-sheet. 

 From the calibration sheet for this ther- 

 mometer we find : 

 Fo=99°. 



<a=20.7° C.± the auxiliary thermometer 

 index correction (in this case 0.0° C.) 

 = 20.7 C. 

 /iL = 6100. 



/=— 0.01° C. (index correction for the 

 main thermometer at 16.4° C). 

 From the paired protected thermometer we 

 find: 



r„=9.12° C. 

 Find: 



(16.40-1-99) (9.12-20.7) 



C= 



<7= 



6100 

 (115.40) (11.58) 



6100 

 C=-0.22°. 

 Find: 



T„= 16.40°-|- (-0.22°) + (-0.01°). 

 r„= 16.17°. 



3-6 REVERSING THERMOMETER CAL- 

 CULATIONS WITH THE SLIDE RULE.— To 



simplify the calculations of reversing ther- 

 mometer corrections, a special oceanographic 

 slide rule was developed. The type used by 

 the Hydrographic Office is shown in figure 3-2. 

 Printed on the face of the slide rule are four 

 scales marked A, B, C, and D. The A-scale 

 gives the values of Fo+T' or Fo+r'„. The 

 B-scale denotes the K— value for each ther- 

 mometer. The C-scale gives the T'-t orr„-<„. 

 The D-scale gives the value C. 



The reverse side of the slide has a three-place 

 table of cosines for wire angles of 1° to 60°. On 

 the back of the slide rule is a depth conversion 

 table for fathoms to meters. 



3-7 Correcting the PROTECTED Ther- 

 mometer with the Slide Rule. — Corrections for 

 the protected thermometer are made with the 

 slide rule as follows: 



Step 1: Fo-f-T'. Determine this value and 

 locate it on the A-scale. 



Step 2: K. Determine K and set its value on 

 the B-scale under the value for Fq-F 7" on the 

 A-scale. 



32 



Step 3: T'~t. Determine this value and 

 locate it on the C-scale. 



Step 4' C- The answer (C) is read from the 

 D-scale directly below the value T' —t on 

 the C-scale. 



The sign of C is plus when T' is greater than t. 



The sign of C is minus when T' is less than t. 



3-8 Correcting the UNPROTECTED Ther- 

 mometer with the Slide Rule. — Corrections 

 for the unprotected thermometer are made with 

 the slide rule as follows : 



Step 1: Fo-|-7"„. Determine this value and 

 locate it on the A-scale. 



Step 2: K. Determine K and set its value on 

 the B-scale under the value for Fo-|- T"„. 



Step 3: T^—t^. Determine this value and 

 locate it on the C-scale. 



Step 4: C. The answer (C) is read from the 

 D-scale directly below the value Ta—t^ on the 

 C-scale. 



The sign of C is plus when Tu, is greater 

 than <„. 



The sign of C is minus when T„ is less than 



tu. 



3-9 THERMOMETRIC DEPTH DETER- 

 MINATION. — After the reversing thermometer 

 readings have been corrected, the thermometric 

 depth for each Nansen bottle equipped with 

 an unprotected thermometer, e. g., the depth 

 at which the thermometers reversed, can be 

 calculated. Such calculations are possible only 

 when protected and unprotected reversing 

 thermometers are paired on a Nansen bottle. 

 UsuaUy protected and unprotected thermom- 

 eters are not paired on every bottle but only 

 at selected depths. 



There are two methods in general use for de- 

 termining thermometric depth. Although simi- 

 lar, one involves direct use of a formula, while 

 the other uses preconstructed graphs based on 

 the formula. Each unprotected reversing ther- 

 mometer has a unique graph called a depth 

 anomaly (AZ) graph from which the depth cor- 

 rection is read directly. 



3-10 Determining Thermometric Depth by 

 Formula. — The thermometric depth may be de- 

 termined directly by the following formula: 



Z= 



Tu-f. 



where : 



Z=The thermometric depth in-meters. 

 r„=The corrected reading of the unpro- 

 tected reversing thermometer. 

 r„=The corrected reading of the protected 

 reversing thermometer. 



H. O. 607 



