598 NOTES TO BOOK X. 



The law of Boyle and Mariotte is not exactly true 

 near the limit at which the air passes to the liquid state 

 in such cases as that just spoken of. The diminution of 

 bulk is then more rapid than the increase of pressure. 



The transition of fluids from a liquid to an airy con- 

 sistence appears to be accompanied by other curious phe- 

 nomena. See Prof. Forbes's papers on the Colour of 

 Steam under certain circumstances, and on the Colours of 

 the Atmosphere, in the Edin. Trans, vol. xiv. 



(TA.) p. 575. To the experiments on steam made by 

 private physicists, are to be added the experiments made on 

 a grand scale by order of the governments of France and of 

 America, with a view to legislation on the subject of steam- 

 engines. The French experiments were made in 1823, 

 under the direction of a commission consisting of some of 

 the most distinguished members of the Academy of Sci- 

 ences; namely, MM. de Prony, Arago, Girard, and Dulong. 

 The American experiments were placed in the hands of a 

 committee of the Franklin Institute of the State of Penn- 

 sylvania, consisting of Prof. Bache and others, in 1830. 

 The French experiments went as high as 435 of Fahren- 

 heit^ thermometer, corresponding to a pressure of 60 feet 

 of mercury, or 24 atmospheres. The American experi- 

 ments were made up to a temperature of 346, which cor- 

 responded to 274 inches of mercury, more than 9 atmo- 

 spheres. The extensive range of these experiments affords 

 great advantages for determining the law of the expansive 

 force. The French Academy found that their experiments 

 indicated an increase of the elastic force according to the 

 fifth power of a binomial 1 + mt, where t is the tempera- 

 ture. The American Institute were led to a sixth power 

 of a like binomial. It does not appear so likely that nature 



