If — = r; 
9 
and on Astronomical Refractions. 
441 
1 
a D (d' O) ^ B p7 {v’ — v} — V — V, 
supposing the heat and the volume to vary, the pressure remaining 
constant. 
According to Dulong the following laws obtain, which however, 
are not admitted by Dr. Apjohn (see L. Sc E. Phil. Mag. 1838, 
vol. xiii. p. 339) : 
Des volumes egaux de tous lesfluides elastiques pris a une 
ineme temperature et sous une meme pression, etant comprimes 
ou dilates subitement d’une m^me fraction de leur volume, dega- 
gent ou absorbent la meme quantite absolue de chaleur. 2°. Les 
variations de temperature qui en resultent sont en raison inverse 
de leur chaleur specifique a volume constant.” — -Mem. de V Institute 
tom. X. p. 188. 
According to the first of these laws the quantity B must be the 
same for difierent vapours; of the second 1 am unable to offer any 
satisfactory interpretation. 
In what follows I propose to ascertain how far the equations [1] 
and [2] satisfy the best observations on record. The general rela- 
tion gives 
1 + a 3" = (1 + a 8) y -E) , 
(/'“-£) 
Eliminating E between this equation and that which connects 
and p', 
-9) (1+ « d')(p'^-p-^)=={Q'--d) 
If 1:^= /s 
(£)■-! ir - ,) (X ) 
(.■-.) + 
From this equation, knowing 0'', 0', Q, p”, p', p; /3 may be deter- 
mined for any gas or vapour. Knowing /3, E may be found from 
the equation 
/(L.,)-/(±,.) 
^ “ 0' - 0 
[To be continued.] 
Piiil. Mag. S. 3. Vol. 16. No. 104. Map 1840. 2 G 
