4713 



HYDROGRAPHIC MANUAL 



Page 402 



The first column may be considered for practical purposes as the observed temperature or temper- 

 ature at time of thermometer reversal. The entries in the three columns under the second heading are 

 the corrections to be applied (algebraically to the observed temperatures) for three different temperatures 

 of air in the thermometer at the time of reading. The National Bureau of Standards determines, by 

 actual comparisons against the standard, only those corrections shown in parentheses; the other cor- 

 rections are computed. The coefficient of expansion of the glass and the volume of the supplemental 

 reservoir to the mark at 0° C, which is furnished in the report of the test, are needed to compute these 

 other corrections. The volume is the amount of mercury contained in the supplemental reservoir 

 below the zero graduation and is expressed in the equivalent number of degrees the mercury would 

 occupy in the capillary tube. This is known as the degree-volume of the thermometer. Computa- 

 tions involving the above data are not required in the field and are explained only for a better under- 

 standing of the National Bureau of Standards report. It is apparent that the magnitude of the 

 corrections in parentheses is an indication of the accuracy of the thermometer. The corrections should 

 be small if the thermometer is accurately graduated and uniform if the size of the capillary tube is 

 uniform. The magnitude of the computed corrections varies with the degree-volume of the ther- 

 mometer and depends on the volume of the supplemental reservoir; if the degree-volume is large, the 

 corrections are large and they will have to be applied to observed temperatures. 



4713. Corrections to Observed Temperatures 



' Thermometer corrections may be conveniently obtained from a graph, as in figure 85, plotted on 

 cross-section paper from the correction values of the National Bureau of Standards report. The 

 temperatures of the enclosed air column when the reversing thermometer is read are plotted as 

 abscissas at convenient divisions of the cross-section paper. The corrections to be applied, minus 

 below and plus above a zero line, are plotted as ordinates. All of the corrections in the report are 



DEEP-SEA THERMOMETER 



MAKERS NO. T28297 . 



INTRINSIC 



ERROR OF 



THERMOMETER 



TEMPERATURE OF AIR COLUMN 

 AT TIME REVERSED THERMOMETER IS READ 



Figure 85. — Example of thermometer correction graph. 



plotted and the points for each corresponding observed temperature connected. These lines will 

 furnish only corrections for the three observed temperatures tabulated, i. e., 0°, 15°, and 35°. The 

 intermediate lines for each 5° should be interpolated between these by subdivision of the intervening 

 spaces. It is to be noted that the calibration curve of a reversing thermometer retains its shape but 

 shifts slightly along the ordinate as the thermometer ages. 



To determine the correction to be applied to an observed temperature, the temperature of the 

 enclosed column of air must be known. This may be determined by several methods. The reading 

 of the thermometer may be deferred until the temperature of the enclosed column reaches the tempera- 

 ture of the atmosphere but this will require from 15 to 20 minutes, depending on the difference in 



