Ox THE MECHANICAL EQUIVALENT OF HEAT 387 



Taking the average of the two, it would seem that No. 6163 stood 

 about -015 higher than the mean of 7334 and 7316 at the 20 point, 

 or 6163 has a higher value of ra by -000045 than the others. 



These differ about -17 from the air thermometer at 40, which gives 

 the value of m about -000104. Whence m for 6163 is -00015, as we 

 have found before by direct comparison with the air thermometer. 



I am inclined to think that the former value, -00018, is too large, 

 and to take -00015, which is the value found by direct comparison, as 

 the true value. As the change, however, only makes at most a differ- 

 ence of 0-01 at any one point, and as I have already used the previous 

 value in all calculations, I have not thought it worth while to go over 

 all my work again, but will 'refer to the matter again in the final 

 results, and then reduce the final results to this value. 



m. CALOKIMETKY 

 (a) Specific Heat of Water 



The first observers on the specific heat of water, such as De Luc, 

 completed the experiment with a view of testing the thermometer; and 

 it is curious to note that both De Luc and Flaugergues found th tem- 

 perature of the mixture less than the mean of the two equal portions 

 of which it was composed, and hence the specific heat of cold water 

 higher than that of warm. 



The experiments of Flaugergues were apparently the best, and he 

 found as follows : " 



3 parts of water at and 1 part at 80 R. gave 19 -86 K. 

 2 parts of water at and 2 parts at 80 R. gave 39 -81 R. 

 1 part of water at and 3 parts at 80 R. gave 59 -87 R. 



But it is not at all certain that any correction was made for the 

 specific heat of the vessel, or whether the loss by evaporation or radia- 

 tion was guarded against. 



The first experiments of any accuracy on this subject seem to have 

 been made by F. E. Neumann in 1831. 21 He finds that the specific 

 heat of water at the boiling point is 1-0127 times that at about 28 C. 

 (22 R.). 



The next observer seems to have been Regnault, 22 who, in 1840, 



M Gehler, Phys. Worterbuch, i, 641. 

 "Pogg. Ann., xxiii, 40. 

 22 Ibid., li, 72. 



