AEROSTATICS. 239 



If the centesimal thermometer is used,/= (1.376) 100 ' 



DALTON'S New System of Chemical Philosophy, part i. 

 . p. 44. GAY LUSSAC had deduced the same conclu- 

 sion from his experiments. 



When the variations of heat are small, or not exceed- 

 ing the ordinary vicissitudes of heat and cold in the 

 atmosphere, the variations of elasticity and of bulk 

 may be supposed proportional to them. In such 

 cases the expansion of air, or of any other per- 

 manently elastic fluid, calculated from the prece- 

 ding formula, is .004 for a centesimal degree, or 

 .00222 for a degree of FAHRENHEIT. 



In this estimation of the elastic force of fluids, the 

 thing actually measured is the expansion produced 

 by the heat, while the compressing force remains 

 the same. The force that would be required to 

 reduce the fluid into its former dimensions, the 

 temperature being the same, is the direct measure 

 of the increase of elasticity. On the supposition, 

 however, that, when the temperature is given, the 

 elasticity is inversely as the space which the fluid 

 occupies, the absolute increase of the elasticity, pro- 

 duced by an increase of temperature, is proportional 

 to the expansion. This supposition will be shewn to 

 hold of air and other elastic fluids. 



334. Heat is mechanically produced by Percus- 

 sion and Friction. 



This 



