318 



REPORTS ON THE STATE OF SCIENCE. 



of by diflFerence, as is necessarily the case when (as in Holboru and 

 Henning's experiments) the whole internal energy change associated 

 with complete cooling of the gas is measured. 



In view of the great difference in the method of experiment a 

 comparison of Clerk's results with those of Messrs. Holborn and Henning 

 is of great interest. Clerk's measurements extended to 1450° C, but 

 those above 1200° C. were based on the first expansion line after the 

 explosion when the method for getting heat loss would be of doubtful 

 application, and when, moreover, combustion may have been incomplete. 

 It will be better, therefore, to confine the comparison to temperatures 

 of 1200° and below. The following table exhibits the internal energies 

 of the mixed gas with which Clerk experimented calculated from Holborn 



and Henning's figures, together with the energy calculated from Clerk's 

 values for the mean volumetric heat. The energies are, as usual, reckoned 

 from 100° C. ; and the energies of an ideal gas with a constant volumetric 

 heat of 4-9 are added for comparison. 



It will be seen that Clerk's results are throughout about 10 per cent, 

 higher than the others. The diffei-ence between the energy of the real 

 and of the ideal gas, the discovery of which is the true object of these 

 experiments, is about twice as great in the one case as in the other. It 

 does not seem possible to account for so large a discrepancy by ordinary 

 experimental errors. It must be due either to some systematic error 

 inherent in the method of experiment in one or both cases, or to a 

 difference in the conditions of experiment giving I'ise to a real difference 

 of internal energy. 



