On the Determination of the Specific Heat of Steam. SSI 



trical experiments) that there is a temperature-level in nature 

 for the incandescence of gases, much lower than that of the low- 

 temperature oxvgen-spectrurn of these pages. Wherefore, if 

 we could artificially produce that kind of ultra-low-temperature 

 illumination, electric probably, we might find that the u (alpha) 

 band in the solar sunset spectrum represented the oxygen, 

 while the A and B bands showed us the nitrogen gas thereof — 

 they two being the mighty gas constituents known so well to 

 every one {except telluric-line solar spectroscopists) to exist in 

 the earth's atmosphere, and in such overpowering quantity as 

 to practically exclude every thing else except watery vapour. 



XL. Eegnault's Determination of the Specific Heat of Steam. 

 By J. Macfablajse Gkat*. 



~D EGKNATJLT'S experiments on the specific heat of vapours 

 JA' have been interpreted by Begnault as giving results 

 not at all in accordance with the deduction from the kinetic 

 theory of gases, that, for matter travelling in single mole- 

 cules, the product of the molecular weight by the specific heat 

 is a constant for all substances. I have been led, by consider- 

 ing the order of temperature-pressures for steam, to conclude 

 that the above deduction is true for steam; and I have no doubt, 

 also for all matter travelling in single molecules. When, in 

 1880, I laid my conclusions before the Physical Society as 

 being corroborated by Eegnault's dynamical experiments, it 

 was objected that Eegnault's direct thermal experiments gave 

 results widely different from my conclusions : and the report 

 on my paper was that that difference proved that, in the cor- 

 roborations I had pointed out, I had been led away by merely 

 numerical coincidence. 



I will now show that Eegnault's thermal experiments have 

 been misinterpreted by Eegnault himself, and that he ought to 

 have read the specific heat of steam, according to his experi- 

 ments, to be exactly in accordance with the deduction of the 

 kinetic theory. 



The method of the experiments was to generate steam at 

 100° C, to superheat it under atmospheric pressure to (say) 

 125° in one set of experiments, condensing it in a calorimeter 

 to ascertain what quantity of heat was given up, down to { < z . 

 In a second set of experiments with the same apparatus, the 

 temperature was raised to (say) 22b c . while the steam was 

 still at atmospheric pressure ; this was also condensed in the 



* Communicated by the Physical Society, havirg been read at the 

 Meeting on February 25, 1882. 



