DEEP-SEA REVERSING THERMOMETERS 237 



Normally, a shift ot zero point should be reflected equally in the scale corrections throughout the 

 whole range of a conventional thermometer, and this holds good also for protected reversing thermo- 

 meters. Correction graphs for each calibration of all the thermometers listed in Table i have been 

 drawn and, with only a few exceptions, there is a considerable similarity in the general trend of the 

 correction curve at each calibration of individual thermometers. Those made by Richter and Wiese 

 show, in general, less variation in the scale corrections required over the whole range, and over the 

 years but, despite the larger and sometimes more irregular scale corrections required to a number of 

 the thermometers made by Negretti and Zambra (possibly because of a slightly more irregular bore 

 in the glass tubing), there is a more marked similarity in the trend of the various calibration curves for 

 each instrument. Since it is easier to demonstrate the change of zero and scale corrections graphically, 



-g. Of CORRECTION 



N° 86} Ri K 



Fig. I 



Fig. 2 



typical correction graphs for two German and three British thermometers have been selected and 

 appear as Figs. 1-5. Each comprises the correction curves for the various calibrations, with the 

 actual scale correction plotted against the scale range. 



Effect of the Volume of Mercury (F,,)* 

 Of the thirteen German-made thermometers listed in Table i three (nos. 863, loii and 1257) have 

 been extensively used, especially no. 1257 with which 459 observations were made between 1928 and 

 1939. Four others were used to a lesser degree, whereas the remaining six appear to have had little 

 or no use. Unfortunately the early history of these thermometers is obscure as notes on their per- 

 formance were not regularly kept. We cannot say, therefore, whether they are reliable, or whether 

 they had been used and found erratic. 



On the other hand the stock of reversing thermometers carried in the ships has always been well in 

 excess of immediate demands. Once in use a good working set of thermometers remained so until 

 individual instruments were lost, or broken, or became erratic in their action. In these circumstances 



* F„ is the volume of mercury, in degrees, reversed at 0° C. It is determined for each thermometer by the maker. It is not, 

 so far as we are aware, re-determined at any subsequent re-cahbration, 



2 D X.\I,\ 



