t 



356 HENRY A. EOWLAJSTD 



is only fair, but we must remember that the same specimens of glass 

 were not used in this experiment as in the others, and that for these 

 specimens the agreement is also poor above 100. The values a = 

 .000,000,44 and & = 260 are much better for these specimens, and 

 the seventh column contains the values calculated from these values. 

 These values also satisfy the observations above 100 for the given 

 specimens. 



The table seems to show that between and 100 a thermometer of 

 Choisy-le-Eoi almost exactly agrees with the air thermometer. But 

 this is not at all conclusive. Regnault, however, remarks, 4 that be- 

 tween and 100 thermometers of this glass agree more nearly with 

 the air thermometer than those of ordinary glass, though he states 

 the difference to amount to -1 to -2 of a degree, the mercurial ther- 

 mometer standing below the air thermometer. With the exception of 

 this remark of Eegnault's, no experiments have ever been published 

 in which the direction of the deviation was similar to this. All ex- 

 periments have found the mercurial thermometer to stand above the 

 air thermometer between and 100, and my own experiments agree 

 with this. However, no general rule for all kinds of glass can be 

 laid down. 



Boscha has given an excellent study of Eegnault's results on this 

 subject, though I cannot agree with all his conclusions on this subject. 

 In discussing the difference between and 100 he uses a formula of 

 the form 



T 1= t(lOQ t), 

 ct 



and deduces from it the erroneous conclusion that the difference is 

 greatest at 50 C., instead of between 40 and 50. His results for 

 T t at 50 are 



Choisy-le-Eoi .22 



Verre Ordinaire +.25 



Verre Vert +.14 



Yerre de- Suede +.56 



and these are probably somewhat nearly correct, except the negative 

 value for Choisy-le-Eoi. 



With the exception of Eegnault, very few observers have taken up 

 this subject. Among these, however, we may mention Eecknagel, who 



4 Comptes Rendus, Ixix. 



