268 PROCEEDINGS OF THE AMERICAN ACADEMY. 



and to remain standard for sixty years. He himself deduced from 

 them the well-known linear formula 



H= 606.5 + 0.305 t calories. 



Others have represented them by second degree formulae with negative 

 second degree terms. 



The more modern experimental work began in 1889 with a measure- 

 ment of L at 0° C. by Dieterici. 3 He was followed by Griffiths, 4 Joly 5 

 and Smith, 6 working at various temperatures between 0° and 100° C, 

 and finally in 1906 by Henning, 7 of the Reichsanstalt, who published 

 an excellent series of values covering the range from 30° to 100° C. 

 The results of all these observers are in excellent agreement and show 

 that Regnault's formula for H gives values which are much too high 

 near 0° and somewhat too low near 100°. 



In 1908 the formula which is the basis of this paper was presented 

 to the American Physical Society 8 and to the American Society of 

 Mechanical Engineers. 9 It was based on the results of certain throttling 

 experiments by Grindley, 10 Griessmann 11 and Peake. 12 These experi- 

 ments were originally undertaken for the purpose of computing, with 

 the help of Regnault's total heats, the variation with pressure and 

 temperature of the specific heat, Cp, of superheated steam. This 

 attempt was unsuccessful, because the total heats entered into the 

 computations in such a way as to cause the errors in them to be 

 tremendously magnified in the results. The desired information about 

 C p has since been obtained in other more direct ways, and the throt- 

 tling experiments have been ignored. It is, however, possible, by 

 reversing the computation processes of Grindley, Griessmann and 

 Peake, to proceed from the recently determined values of C p which 

 were to have been their goal, back to a new determination of the 

 values of H which were their starting point. The very sensitiveness 

 of their procedure to errors in H ensures the insensitiveness of the 



3 Wied. Ann., 1889, 37, 494. 



* Phil. Trans., 1895, 186 A, 261. 



B In an appendix to Griffiths' paper, page 322. 



• Phys. Rev., 1907, 25, 145. 

 » Wied. Ann., 1906, 21, 849. 

 » Phys. Rev., 190S, 26, 407. 

 9 Journal, loc. cit. 



" Phil. Trans., 1900, 194 A, 1. 



11 Zeit. Ver. d. Ing., 1903, 47, 1852, and 1880; also Forschungsarb., 1904, 

 13, 1. 



" Proc. Roy. Soc, 1905, 76 A, 185. 



