74 DKS. J. A. HARKER AND P. CHAPPUIS OX A 



XXX. PRELIMINARY DETERMINATIONS. 

 (a) Measurement of the Capacity of the Thermometric Reservoir. 



Before proceeding to the measurement of the capacity of the therinometric reservoir, 

 we considered it advisable to subject it to a prolonged annealing at the temperature 

 of the boiling-point of sulphur. After thirteen hours' heating we obtained for its 



capacity at 



V = 159*670 cub. centims., 



and after a second exposure of eleven hours we found 



V = 159-642 cub. ceutims. 



This value was a little modified during the operation of mounting the thermometer, 

 as a short piece of the connecting capillary had to be suppressed. Allowing for this 

 we found for the first part of the experiments the value 



V = 159-629 cub. centims. 



(b) Coefficient of Dilatation of Hard Glass. 



The dilatation of " verre dur " was not measured directly on the thermometric 

 reservoir itself, but on a tube of 1 metre length drawn from the same melting ; its 

 linear dilatation was determined by a long series of experiments at temperatures 

 comprised between and 100. These experiments have given for the law of cubic 

 dilatation of glass between and 100 the formula 



V, = V (1 + O'OOO 021 801 t + O'OOO 000 015 536 ?), 



whence, for t = 100, 



V 100 = V (1 + 0-002 335 50). 



During some subsequent experiments on the effect of prolonged heating on glass, 

 we had occasion to control this result by determining the dilatation between and 

 100 of a " verre dur" vessel drawn from the same tube as the thermometric reservoir. 

 From these observations we found 



(1) Before annealing V 100 = V (l + 0'002 357 1), 



(2) After annealing at 445 for 81 hours . . V 100 = V (1 + 0'002 343 6). 



These last measurements furnish no indication of the magnitude of the term in t~, 

 which alone has any influence on the temperature measurements. We have therefore 

 employed, for all the observations relative to the glass reservoir, the expression with 

 two terms indicated above. 



