DAVIS. — CERTAIN THERMAL PROPERTIES OF STEAM. 285 



These average deviations are, of course, very small, but the larger 

 deviations in each group tend to cluster and to approach the limit 

 of accuracy of the measurements, so that the systematic variation may 

 be real. In any case, its amplitude is so small that it deserves but 

 little consideration at this time. 



4. Discussion op the Specific Heat of Superheated Steam. 



It is the purpose of the rest of this paper to collect and revise such 

 useful computations of other thermal properties of steam as are 

 affected by a change in the accepted values of the total heat of 

 saturated steam, together with such other results as are valuable for 

 comparison with them. Section 4 will be concerned with the specific 

 heat of superheated steam. Many papers on this subject have been 

 published during the last ten years, especially in the technical press. 

 They can be roughly classified under the following heads. 



A. Direct experimental determinations. 



B. Indirect experimental determinations and computations from 

 other data. 



a. Throttling experiments. ( 



b. Computations based on characteristic equations or on volume 



measurements. 



c. Computations based on the Joule-Thomson effect. 



d. Computations along the saturation line based on Planck's 



equation. 



e. Other computations. 



C. Resumes and discussions. 



Each of these possible sources of information will be discussed in turn, 

 with the object, not so much of reviewing previous papers, as of getting 

 by each method the best information that the new material in this and 

 in the preceding paper makes possible. 



A. Direct experimental determinations. — Three of the papers that 

 belong in this subsection have already been discussed in Section 2. 

 The conclusion there reached was that of the three, that of Knoblauch, 

 Linde and Klebe was the most reliable. Their results will therefore 

 be used as the point of departure of this section, it being the object 

 of each subsection, either to test the justice of the decision that their 

 work is preferable to Thomas ', or to determine what changes should 

 be made in their curves to bring them nearer to the truth. 



The most famous of all contributions to this subject is Regnault's 

 direct experimental determination of C p in 1862. 33 It seems not to be 



33 Mem. Inst, de France, 1862, 26, 167. 



