1836.] 



of the Wet-bulb Hygrometer. 



427 



At any rate it must be conceded that the method itself possesses 

 superior facility to the process of De la Roche and Berard*, also fol- 

 lowed by HAYCRAFTf, or to that more recently followed by my friends 

 Messrs. F. Marcet and De la Rive of GenevaJ. 



It may be as well to recite the conflicting values arrived at by 

 these and other authors, including M. Dulong§, whose mode of in- 

 vestigation by the velocity of sonorous vibrations in the respective 

 gases, was most ingenious in itself, and perhaps better entitled to 

 respect than any other. 

 Tab. XII. — Specific heat of gaseous bodies by volume, under constant pressure. 





By De la Roche 



By Haycraft 



By Marcet 



By DuLong 



By wet-bulb 





and Berard. 





and De la Rive. 





depression. 



Atmospheric air, 



1,000 



1,000 



J, 000 



1,000 



1,000 





976 



1,000 



1,000 



1,000 



— 



Hydrogen, .... 



903 



1,000 



1,000 



1,000 



1,220 





1,000 



1,000 



1,000 



1,000 



— 



Carbonic Acid. . 



1,258 



1,000 



1,000 



1,175 



1,087 



Carburett. Hyd. 



1,553 



1,060 



1,000 



1,531 



— 



Carbonic oxide, 



1,034 



v— 



1,000 



1,000 



— 



Nitrous gas, . . 



1,350 



— 



1,000 



1,160 



— 



Notwithstanding the tendency of my own experiments, every one 

 must feel a prejudice on a view of this table in favor of the conclusions 

 of the English and the Genevese philosophers ; namely, that all 

 the gases have the same specific heat. 



In such case however it will be necessary to assign some other 

 cause for the indubitable results above given, or our judgment must be 

 suspended, until a careful repetition of similar experiments may deter- 

 mine the conditions with other gases, and lead to some definite con- 

 clusions for the whole of this most interesting question. 



§ 5. — A few illustrations of the wet-bulb theory. 



My paper has expanded to such a formidable length, that I am 

 loath to burthen it with many " last words :" yet I cannot refrain 

 from pointing out an instance or two of practical application, and 

 shewing that d and/' are as important elements in the play of mete- 

 orological phenomena as the dew-point itself, and require equally to 

 be studied by naturalists. 



1. The Baron Hugel remarked, that ice was formed in Cashmir 

 with the thermometer at 44° || at an elevation of 15,000 feet : whence 

 he concluded that the freezing point rose as the boiling point fell. 

 This startling paradox is now readily explained : the air of the plains is 

 dry enough at all times in those latitudes : — it becomes relatively drier 

 in expanding on the mountains, while the depression simultaneously 



* Annales de Chiruie, lxxxv. 126. 

 % Ditto 1829, xxxv. 5. 

 || See J. A. S. vol. v. p. 186. 

 3 k 2 



f Annales de Chiniie, xxvi. 298- 

 $ Ditto, x!i. 113. 



