and on Astronomical Refractions. 44 1 



If — = t; 



a.D{0' — e) = BpV {v' — v} = V — V, 



supposing the heat and the volume to vary, the pressure remaining 

 :onstant. 



According to Dulong the following laws obtain, which however, 

 ire not admitted by Dr. Apjohn (see L. & E. Phil. Mag. 183«, 

 rol xiii. p. 339) : 



"1°. Des volumes egaux de tous les fluides elastiques pris a une 

 Heme temperature et sous une meme pression, etant comprim.es 

 )u dilates subitement d'une meme fraction de leur volume, dega- 

 jent ou absorbent la meme quantite absolue de chaleur. 2°. Les 

 •anations de temperature qui en resultent sont en raison inverse 

 le leur chaleur specifique a volume constant."— Mem. de I'Instituf, 

 om. X. p. 188. 



According to the first of these laws the quantity B must be the 

 ame for different vapours; of the second I am unable to offer any 

 atisfactory interpretation. 



In what follows I propose to ascertain how far the equations [1] 

 nd [2] satisfy the best observations on record. The general rela- 

 ion gives 



1 + a 9" = (1 + a 6) JP y --^) , 



ip'^V-E) 



[lliminating E between this equation and that which connects 

 and p\ 



-9) (1+ a S'){p'^-p^) = {5'-^) {l+ocQ"){p"~-''-p~) 



If 1^= /3 



7 



(^)' - 1 (»'- 0) (I + 0" ) 



'rom this equation, knowing 9", 9', 9, p", p',p; /3 may be deter- 

 lined for any gas or vapour. Knowing /3, E may be found from 

 le equation 



E = 



/(^«)-/a-^o 



[To be continued.] 

 Phil. Mag. S. 3. Vol. 16. No. 104. May 1840. 2 G 



