434 Mr. E. H. Griffiths on 



position in which we find ourselves, and our first step should 

 be to apprehend clearly the nature of the difficulties with 

 which we have to contend. 



The first experiments of any accuracy ou this subject seem 

 to have been those of Newman in 1831 *, who found the 

 specific heat of water at boiling-point to be 1*0127 times that 

 at 28°. 



Regnault in 1840 found the " mean thermal unit " to be 

 1-00709 and 1-00890 times that at about 14° C. His prin- 

 cipal experiments, however, were those published in 1850 1, 

 with regard to which Rowland remarks as follows \ : — " It is 

 unfortunate that those experiments were all made by mixing 

 water above 100° with water at ordinary temperatures, it 

 being assumed that ivater at ordinary temperatures changed 

 little, if any. An interpolation formula was then found to 

 represent the results, and it was assumed that the same 

 formula held at low temperatures, even as low as 0° C." 



The assumption thus referred to by Rowland would alone 

 be sufficient to render of little value the conclusions arrived 

 at by Regnault regarding the changes at low temperatures. 



Mr. Macfarlane Gray § has called attention to the fact that 

 there must be some error in the tables given in Regnault's 

 paper, for the columns of data do not agree with the column 

 of results. Wullner || accepts the data columns as correct, 

 and from the re-calculation concludes that the specific heat of 

 water may be taken as constant up to 190° C. Mr. Macfar- 

 lane Gray, however, considers that the error is in the statement 

 of the data, but that Regnault calculated his results from 

 correct data. He is led to this conclusion by the fact that 

 the sum of the weights of the hot and cold water seems in all 

 the doubtful experiments to be greater than the capacity of 

 the calorimeter. On page 452, ibid., is given an account of a 

 careful examination, made by Professor Ryan and Mr. Gray, 

 of Regnault's apparatus which appears to bear out the con- 

 clusions arrived at by Mr. Gray. Whichever view is correct, 

 it is obvious that there is a discrepancy in the numbers as 

 published. Boscha has attempted to correct Regnaultfs results, 

 but, in Comptes Rendus, Regnault has not accepted the cor- 

 rection. 



* Pogg. Ann. xxiii. p. 40. 



t Pogg. Ann. lxxix. p. 241 ; and " De la Chaleur Specifique," Acad, 

 des Sciences, tome xxi. 



X Proc. American Acad., vol. xv. p. 120. 



§ Proceedings Mechanical Engineers. Julv 2, 1889, p. 401. 



|| Expcr. Physic, 1885. 



