1821.] Causes of Calorific Capacity, Latent Heat, fyc. 103 



render the experiment so doubtful as not be able to determine 

 from it whether the law of temperature followed the simple or 

 the subduplicate ratio. With either fluid, therefore, it appears 

 that the calorimeter is not susceptible of that accuracy which 

 experiments of this kind require. Indeed it is questionable 

 whether there is any method so simple and conclusive as that of 

 mixtures. The only things it appears necessary to guard against 

 are loss of temperature by radiation, and the contact of air of a 

 different temperature from the mixture, and the influence of the 

 temperature of the vessel in which the mixture is made. But 

 both these things seem to be almost effectually avoided by an 

 apparatus similar to the one i have described in my experiments 

 on the Ratio and Law of Temperature lately read before the 

 Royal Society; or at least their effects so much diminished as 

 to be nearly, if not wholly, insensible. Any other way of 

 obviating such losses, as by calculation after the manner of 

 Crawford, experience has convinced me is liable to errors and 

 inaccuracies, which might be a little diminished, but, I think, 

 cannot be avoided. 



Some philosophers suppose that the law of heat I have un- 

 folded is the same as that some time since propounded by Mr. 

 Dalton ; there is, however, scarcely the least similarity between 

 them. Mr. Dalton thinks the expansions of all fluids are pro- 

 portional to the squares of their temperatures from the points of 

 their greatest density, but these points of greatest density are not 

 here taken into account, nor do 1 even make the rate of the fluid 

 expansions hold any part in my investigations. The theory that 

 I have given, so far as I have yet delivered it, is wholly inde 

 pendent of the law or laws of fluid expansion, and does not even 

 consider whether fluids expand by general or particular lews, 

 nor whether they have points of greatest density or not. Mr. 

 Dalton's theory makes the expansions of all gaseous bodies to 

 follow a geometrical progression, while the temperatures follow 

 an arithmetical; or that the temperatures from some given point 

 are as the logarithms of the expansions ; but, according to my 

 theory, the squares of the true temperatures are as the volumes, 

 and, therefore, the first differences of the volumes, or the 

 increments of expansion, are proportional to the second differ- 

 ences of the corresponding temperatures — a law which differs 

 materially from Mr. Dalton's; for his increments of temperature 

 bear no ratio whatever to any order of the differences of expan- 

 sion. Notwithstanding, however, this wide difference between 

 the two laws, it must be confessed that Mr. Dalton has 

 approached nearer to the ideas \ have developed than any other 

 philosopher 1 know of; and had he applied his views of fluid 

 expansion to Leases, he would have anticipated the general law 

 of temperature I have given. 



(To be continued.) 



