﻿Expansion of 'Mercury and of Quartz. 655 



Specific volume of water with respect to that at 4°. 

 Variations from the absolute value X 10 G . 



Temperature. 



Obappuis. 

 Verre Dur. 



Chappuis. 

 Platinum-Indium. 







- 1 



• 



-1 



10 



_o 



-3 



20 



~5 



-3 



SO 



— 7 



-4 



40 



-11 



-5 



100 



— 22 





It will now be noticed that there is a systematic difference 

 between the two sets of results. The platinum-iridium bulb 

 (a more isotropic material) shows a better agreement. The 

 glass bulb shows quite sensible differences. If then we can 

 assume that the absolute method is free from systematic 

 error, the only conclusion we can come to is that the 

 expansion of the glass has not been properly allowed for. 

 The linear expansion was, in this case, measured on the bulb 

 itself, and hence should be especially reliable. It is note- 

 worthy that Chappuis' value at 100° agrees well with that 

 obtained by Thiessen, Scheel, and Sell with the weight 

 thermometer, showing that, if the absolute method can be 

 trusted, a similar error has been made in the two cases in 

 allowing for the expansion of the glass. 



The agreement in §5 (p. 415) is satisfactory as determining 

 the fundamental interval for mercury. The values originally 

 given varied from 18194 to 18257, when the expansion of 

 the bulb was allowed for by the linear method. The agree- 

 ment is thus obtained by frankly abandoning this method 

 for the dilatation, and reverting to the absolute method. 

 ChappmV numbers, treated in the same way, lead to a some- 

 what higher value, viz., 18276 ; this should have been 

 included in the list of §5, but it would have somewhat 

 marred its symmetry. 



The experimental evidence so far available thus seems 

 distinctly against the calculation of the cubical from the 

 linear expansion. 



University College, 

 London. 



