OF ARTS AND SCIENCES. 197 



t 



V. CONCLUDING REMARKS. AND CRITICISM OF RESULTS 

 AND METHODS. 



On looking over the last four columns of Table LIII., which gives 

 the results of the experiments as expressed in terms of the different 

 mercurial thermometers, we cannot but be impressed with the unsatis- 

 factory state of the science of thermometry at the present day, when 

 nearly all physicists accept the mercurial thermometer as the standard 

 between 0° and 100°. The wide discrepancy in the results of calori- 

 metric experiments requires no further explanation, especially when 

 physicists have taken no precaution with respect to the change of zero 

 after the heating of the thermometer. They show that thermometry 

 is an immensely difficult subject, and that the results of all physicists 

 who have not made a special study of their thermometers, and a com- 

 parison with the air thermometer, must be greatly in error, and should 

 be rejected in many cases. And this is specially the case where 

 Geissler thermometers have been used. 



The comparison of my own thermometers with the air thermometer 

 is undoubtedly by far the best so far made, and I have no improve- 

 ments to offer beyond those I have already mentioned in the " Ap- 

 pendix to Thermometry." And I now believe that, with the improve- 

 ment to the air thermometer of an artificial atmosphere of constant 

 pressure, we could be reasonably certain of obtaining the tempera- 

 ture at any point up to 50° C within 0.'°01 C. from the mean of two 

 or three observations. I believe that my own thermometers scarcely 

 differ much more than that from the absolute scale at any point up to 

 40° C, but they represent the mean of eight observations. However, 

 there is an uncertainty of 0.°01 C. at the 20° point, owing to the un- 

 certainty of the value of m. But taking m = .00015, I hardly think 

 that the point is uncertain to more than that amount for the ther- 

 mometers Nos. 61G3, G165, and G1GG. 



As to the comparison of the other thermometers, it is evidently 

 unsatisfactory, as they do not read accurately enough. However, the 

 figures given in Table LIII. are probably very nearly correct. 



The study of the thermometers from the different makers intro- 

 duces the question whether there are any thermometers which stand 

 below the air thermometer between and 100°. As far as I can find, 

 nobody has ever published a table showing such a result, although 

 Boscha infers that thermometers of "Cristal de Choisy-le-Roi " should 

 6tand below, and his inference has been accepted by Regnault. But 

 it does not seem to have beeu proved by direct experiment. My 



