Hough — Heat Vaporisation of Water, etc. 



R 



/Vx-T'J^ 





< 



= 



uj 

 w',R 







= 



??? I 



m'R 



m 



W — mL 

 W - w'L 







m'K~ 





m 



1 /W 



— 



W'\ 



w7 



where R = ratio of the conductivity 

 capacities of the two 

 cylinders. 



In the second term of the right hand member the two fac- 

 tors alw T ays have opposite signs. The correction is therefore 

 a negative quantity. By reducing the conductivity capacity 

 of the rubbers and increasing that of the cylinder, this correc- 

 tion is reduced to a minimum. Only the ratio of the conduc- 

 tivity capacities is demanded by this formula, not the specific 

 conductivities. This ratio is determined by the method of 

 cooling. 



The advantages of this method are : the measurement of all 

 quantities involved to a high degree of accuracy, depending 

 only on the skill of the mechanician : the elimination of all 

 errors due to thermometry, the calorimeter constant, the water 

 vapor in the steam, radiation and convection : the minimiza- 

 tion and rigorous correction for conduction. 



Preliminary tests of the most rigorous type show that all the 

 factors that enter into this result are entirely within control. 

 A long series of observations are to be made during the coming 

 year, from which it is confidently expected that a value accurate 

 to at least one part in a thousand will be obtained. • 



University of Pennsylvania. 



