the late Dr. Joule's Thermometers. 



481 



Table I. 



1 



Division. 



Distance from 

 centre of bulb. 



Distance between 

 successive intervals 



Pressure 

 correction in 







of 50 divisions. 



degrees. 







9-2 





00234 



23-3 (zero) 



11-1 





•0284 



50 



134 



4-2 



•0343 



100 



17-7 



4-3 



•0453 



150 



22-2 



4-5 



•0567 



200 



26-7 



4-5 



•0683 



250 



31-4 



4-7 



•0802 



300 



36-1 



4-7 



•0922 



350 



40*8 



4-7 



•1042 



400 



45-6 



4-8 



•1165 



450 



50-6 



5-0 



•1292 



500 



55-7 



5-1 



•1423 



550 



609 



5-2 



•1556 



600 



66-0 



51 



•1686 



650 



71-2 



5-2 



•1819 



700 



765 



5-3 



•1955 



750 



81-8 



5-3 



•2089 



To calculate the pressure correction we require the dis- 

 tances from the centre of the bulb, but there must of course be 

 some uncertainty as to the point which is chosen as centre. 

 The figures in the third column were obtained by direct 

 measurement and are not affected by the same uncertainty. 

 It will be seen that the bore is conical, gradually diminishing 

 in diameter. The mean cross-sections near the two ends of 

 the tube differ by about 20 per cent. 



In addition to the differences in the length of division 

 intended to correct for the changes in the bore, there are also 

 not inconsiderable inequalities which are evidently due to 

 faults of graduation. These irregularities are quite visible 

 with the naked eye, two successive intervals differing occa- 

 sionally by as much as the tenth part of their own length. 

 Owing to this fact the error of a single reading of this 

 thermometer A may amount to 0°*004 C. quite independently 

 of the general errors of calibration. It must be remembered 

 of course that at the time the thermometers were made such 

 a quantity was not considered to be of any importance, so 

 that the divisions were sufficiently accurate for the purposes 

 for which they were originally intended, 



