Knowledge of the Specific Volumes of Steam. 15 



nault's thermometric scale, which will be denoted as Regnault's 

 calorie. The formula may be incorrect towards 200° by about 

 0*3 per cent, but is quite accurate at 100°, since in this vicinity 

 the corrections are very slight whatever be the thermometric 

 scale. It gives for the mean specific heat between 0° and 100° 

 the value 1-00358. 



Now if Regnault's scale was that of the air-thermometer, 

 this number should agree with the determinations made by 

 other observers who have used that scale or ones not differing 

 essentially from it. Such determinations have been made by 

 Yon Muenchausen,* Rowland, f Henrichsen,J Baumgartner,§ 

 Yelten|| (two series, one by the method of mixtures, the other 

 with the Bunsen ice-calorimeter), Dieterici,!" Ludin,** Joly,ff 

 and Reynolds.:);;); 



Yon Muenchausen's work, which was conducted by the 

 method of mixtures, has been criticised by Rowland on the 

 ground that the experiments were performed in an open 

 vessel. An inspection of his tables reveals great discrepancies. 

 Thus as a mean of row I he finds that the mean specific heat 

 from 26°*70 to 42°*37 is 1-0033 times that from 20°'07 to 

 26 o, 70. This is impossible, for the specific heat reaches a 

 minimum at 32°, by Rowland's experiments, and there would 

 be necessitated a mean specific heat from 32° to 42° of 1*0033, 

 the specific heat at 15°, <? 15 , being the unit. This mean specific 

 heat would indicate for c„ the value 1-0102, an increase of 1*4 

 per cent in ten degrees. Moreover in rows 11 and III he finds 

 that the mean specific heat from say 25°-7 to 42°*7 is 1*0037 

 times that from 17°*3 to 25°'7, an increase over the preceding, 

 whereas according to Rowland's data it should be less. His 

 formula makes c _ 100 equal to 1'015 c 15 . 



The writer has made careful comparisons of a similar nature 

 of the experiments of Baumgartner and Yelten, and finds 

 even worse discrepancies. Baumgartner makes the mean 

 specific heat from 0° to 100° equal to 1*016 <? 15 , while Yelten's 

 two series make it respectively 0*9896 and 0*9929. 



The experiments of Henrichsen were performed with the 

 ice-calorimeter. Dieterici, who is an authority on the use of 

 this instrument, has made a careful comparison of them with 

 those of Yelten carried out by the same method. He says 

 (reference, p. 443) : " The great differences which the experi- 

 ments made with the ice-calorimeter show, make it probable 

 that this instrument is unsuited for this investigation." More- 



*Wied. Ann., i, p. 592, 187?. f Proc. Amer. Academy, 1879-80, p. 120. 



% Wied. Ann., viii, p. 83, 1879. § Ibid., viii, p. 648, 1879. 



|| Ibid., xxi, p. 31, 1884. j[ Ibid., xxxiii, p. 417, 1888. 



** Beiblaetter zu Wied. Ann., xx, p. 764, 1896. 



ff Phil. Trans., clxxxvi a, pp. 322, 323, 1895. \\ Nature, June 3, 1897. 



