98 



temperature of boiling water. In fact this agrees nearly with 

 Mayer's conclusions made long before. It becomes there- 

 fore for t degrees of the thermomeicr = 1 +,002083 (J — 3'2) 

 It is not probable that the ratio of expansion is sensibly 

 changed at different heights of the barometer within the 

 limits of its usual variation. That is the ratio of the volum&s 

 at 32° and 212° is the same when the barometer is 58t inches 

 as when 30i inches. 



The increase of height in the barometer from the expan- 

 sion of mercury? by increase of temperature may be consi- 

 dered To^o - for every degree of the thermometer. 



Hence 

 m — 1 : m' — 1 : : density of air bar. b and therm, t : density 

 bar. 29,60 and therm. 50° : : b x j i __ (^_50) x ,0001) 



X 1,0375 : 29,60 x ( 1 + ,002083 (f— 32)) 

 Thereforewi— l = (m'— l)x 2^ x (1— (^— 50),000l)x 



1 ,0375 , 



1+,0020«3 (<— 32) 



The quantity (m' — 1) may be deduced from the experiments 

 of Biot and Arago (Mem. Inst. tom. 7) ^^l^o have most 

 carefully repeated the experiments of Ilawksby, or who ra- 

 ther by a different process, have accurately determined the 

 refractive force of air. They have found when the height of 

 barom. = 0,76 metre and centesimal therm. = that is barom. 

 29,93 inches and F. thermometer = 32° that 

 w— 1 = ,0002946. 



