SSK WILLIAM SIEMENS, F.R.S. 19 



Watt obtained the number 1140 



Regnault 1145 



Dr. Ure 1147 



Desprez, 11 8G, but later li:-2 



Brix 1152 



Gay Lussac and Clement 1170 



Count Rumford 1206 



All of these eminent experimentalists employed essentially the 

 same apparatus, and the differences between their results proves 

 its great liability to error. Brix, of Berlin, was the first to 

 investigate those errors, and to calculate approximately their 

 effect upon the results obtained. 



"While such a large amount of labour and talent has been 

 expended to determine the latent heat in steam of atmospheric 

 pressure, a far more important question seems to have been 

 passed over with neglect, namely, What is the relative amount of 

 heat in steam of various densities ? 



The celebrated Watt justly perceived the importance of this 

 question, but contented himself with one experiment upon which 

 he based his law, "Uiat the sum of latent and sensible heat in 

 steam is the name under all pressures." 



Southern repeated the experiment, and found that steam of 

 greater density contained absolutely more heat than steam of 

 lower pressure, which induced him to adopt the hypothesis that 

 " the latent heat of steam was the same at all pressures" 



Subsequent experiments and general reasoning seemed to be in 

 favour of Watt's law, which enjoyed the general confidence until 

 it was attacked, only a few years since, by Regnault, of Paris, 

 who proved by a series of exceedingly elaborate and carefully 

 conducted experiments, that neither the law of Watt nor that of 

 Southern was correct, but that the truth lay between the two. 

 The apparatus employed by M. Regnault may be said to be a 

 refinement upon those previously employed, and with the 

 advantage of Brix's labours to determine the amount of errors, 

 he seems to have succeeded in measuring the absolute amount of 

 heat in steam of various pressures with surprising accuracy. 



The costly and complicated nature of the apparatus employed 

 by M. Regnault has hitherto prevented other experimentalists 



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