Correction of the Gas-Thermometer. 



69 



was due to an error in the zero pressure, which had to be 

 determined separately under conditions different from those 



Fig. 1.— Comparison of Chappuis' Observations with Results calculated 

 from Cooling-Effect. 



I 



of the thermometric comparisons. A reduction o£ '025 mm. in 

 the zero pressure* was required to make the curve pass through 

 the origin. This correction had the effect of raising all the 

 observations by nearly '007°, which is a quantity of the same 

 order as the difference between the nitrogen and hydrogen 

 scales. If the circled observations in the figure were depressed 

 by -007°, it is evident that they would be brought into rather 

 better agreement with the Joule-Thomson curve between 

 and 25 o& 0., but that the discrepancy below 0° 0. would be 

 increased. The nitrogen observations are seen to be rather 

 more discordant than the hydrogen, but they were taken Qrst 

 in point of time, and the error of the temporary vise of zero 



* The minuteness of this correction (1 in 40,000 on the zero pressure ) 

 indicates the extreme difficulty of the work, which conld not have been 

 carried out successfully without the highest experimental skill ana the 

 most rehned apparatus. 



