274 Mr. Lubbock on the Heat of Vapours 



For oil of turpentine 



p = 1 B - 272 



p' = - & 304 



62^40 0"=330 



30 



P -^ - = [0-2441091]. 



=-1816 y=l-2219 E = -73937. 



And hence for the vapour of aether 

 [2-2601058] 



no i c a 



p~ - -67086 



For the vapour of alcohol 



[2-5396942] 

 p-04025 _ j.57796 



For the vapour of petroleum 



T = [2-6940380] _ ^ 

 p- 6 _ -35294 



For the vapour of oil of turpentine 



T = -04025 - ~~ 4-48. 



^-1816 + .73937 



The temperature being reckoned in Fahrenheit's scale and the 

 pressure in atmospheres. 



Mr. E. Russell has calculated for me the following table, showing 

 how far the above formulae represent the observations of Dr. Ure. 

 The results are exhibited in the plate annexed, and it will be 

 seen that the discrepancies between the theory here suggested and 

 the results of observations are chiefly owing to the irregularities of 

 the latter, which arise doubtless from the great difficulties incidental 

 to such experiments. When the pressures are small, the varia- 

 tion of temperature becomes great for a small variation of pressure, 

 so that the agreement of theory with observation may be considered 

 as complete, even if the absolute amount of the error of the calcu- 

 ated temperature is then more considerable. 



