460 Mr. Herapath on True Temperature, and the [Dec. 



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it appears, that the capacity as we ascend in the scale of tem- 

 perature is decreasing, and that the mean capacity between 122° 

 and 212° is to the mean capacity between 32° and 122° as. 140 

 to 151 ; De-Luc found the ratio to be as 14 to 15 in water, and 

 by my experiments the same ratio holds good in mercury. 



By the theory I have expounded, the capacity, as philosophers 

 call it, of every body ought to diminish with the ascent of tem- 

 perature, provided no corpuscular change takes place in the 

 body ; and taken at the temperatures of water freezing and boil- 

 ing, it ought to have a ratio of 1172*6 to 1000, or of 7 to 6 

 nearly. The experiments of Mr. Dalton, Dr. Ure, De Luc, and 

 myself, confirm the general truth of this law in water and 

 mercury, and the experiments of the two latter the correct ratio. 

 The experiments of MM. Dulong and Petit give a different 

 result. They find the capacity of mercury and a few other 

 bodies to be slightly increasing ; but as these philosophers have 

 not published the details of their experiments, it is impossible to 

 say to what sources of error they may have been exposed. Here 

 are at least four testimonies to one against them ; and I have no 

 doubt, if the experiments are carefully repeated, and no corpus- 

 cular change takes effect, that the results, and even the numeri- 

 cal values, will be as I have stated, and not in one kind of bodies 

 only, but in every kind. 



In the body of the proposition, I have stated that the propor- 

 tion of water to the vapour experimented with ought to have an 

 influence in the resulting quantity of latent heat. In general I 

 find thai, the less the ratio of the water to the vapour, the less 

 comes out the value of the quantity of latent heat. Suppose, for 

 instance, that 1 part of vapour at 243*20° Fahr. or 1200 true tem- 

 perature, be condensed on 9 parts of water at 32° Fahr. or 1000 

 true temperature, then, by our theorem, the latent heat would 

 come out 1027-2° Fahr. ; whereas if the same temperatures were 

 used, and there was only 1 part of vapour to 99 parts of water, 

 the latent heat would not exceed 966*72° Fahr. which is 58-i-° 

 below the other result. Here then is a circumstance of which 

 philosophers have never dreamt, and which is nevertheless 

 fully borne out by phenomena. Thus Dr. Ure, by condensing 

 steam on water in the proportion of 1 to 161*7, finds the latent 

 heat to be 888-i- ; while Count Rumford, by using the propor- 

 tion of 1 to 114, finds it 1018*6°, and with the proportion of 1 

 to 96*1, as much as 1023^°, the experiment being conducted 

 in the same way, and with the same apparatus. We have here 

 not only the testimony of the experiments of two philosophers 

 for the truth of our general position, but what is in this case of 

 infinitely greater consequence, the testimony of experiments 

 made by the same individual with the same apparatus. 



