RELATION OF VAPOR AND AIR. 175 



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 

 Sciences; 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 Pennsylvania, consisting of Prof. 



v O 



Bache and others, in 1830. The French experiments went as high 

 as 435 of Fahrenheit's thermometer, corresponding to a pressure of 

 CO feet of mercury, or 24 atmospheres. The American experiments 

 were made up to a temperature of 346, which corresponded to 2Y4 

 inches of mercury, more than 9 atmospheres. 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 binominal 1 -f mf , where t is the temperature. The 

 American Institute were led to a sixth power of a like binominal. 

 Other experimenters have expressed their results, not by powers of 

 the temperature, but by geometrical ratios. Dr. Dalton had supposed 

 that the expansion of mercury being as the square of the true tem- 

 perature above its freezing-point, the expansive force of steam increases 

 in geometrical ratio for equal increments of temperature. And the 

 author of the article Steam in the Seventh Edition of the Encyclo- 

 pcedia Britannica (Mr. J. S. Russell), has found that the experiments 

 are best satisfied by supposing mercury, as well as steam, to expand 

 in a geometrical ratio for equal increments of the true temperature. 



It appears by such calculation, that while dry gas increases in the 

 ratio of 8 to 11, by an increase of temperature from freezing to boiling 

 water; steam in contact with water, by the same increase of tempera- 

 ture above boiling water, has its expansive force increased in the pro- 

 portion of 1 to 12. By an equal increase of temperature, mercury 

 expands in about the ratio of 8 to 9. 



Pvecently, MM. Magnus of Berlin, Ilolzmann and Kcgnault, have 

 made series of observations on the relation between temperature and 

 elasticity of steam. 20 



Prof. Magnus measured his temperatures by an air-thermometer ; a 

 process which, I stated in the first edition, seemed to afford the bci-t 

 promise of simplifying the law of expansion. His result is, that the 



89 >ee Taylor's Scientific Memoirs, Aug. 1845, vol iv. part xiv., and Ann. dt 

 Chi nve. 



