4*34^ Mr. Lubbock on the Heat of Vapours 
This difference between the original weight of the remainder 
= 0*7500, which amounts to 0*2705, we may consider as 
carbon. 
Now we calculated the amount of carbon to be 0*71188, 
but as we find only 0*2705 grains of carbon, the difference 
= 0*7118 — 0*2705 = 0*4?4?138 carbon, must have been coun- 
terbalanced by an equal quantity of oxygen to produce oxidum 
ferrosoferricum in the following way ; — 
Oxygen 0*44138 
Iron 1*12268 
Oxidum ferrosoferricum . . 1*26406 
Remaining iron , .... 1*040728. 
The 2*604788 
will be therefore the calculated loss ; the actual loss on the 
contrary was found as before mentioned = 2*64; the difference 
between experiment and calculation amounts only to 0*035212. 
[To be continued.] 
LXIV. — On the Heat of Vapours and on Astronomical Re- 
fractions. By John William Lubbock, Esq.^ Treas. R.S. 
F.R.A.S. a?id F.L.S., Vice-Chancellor of the University of 
London^ 4*^.* 
PREFACE. 
^1 ''HE connexion between the temperature and the pressure 
(or elasticity) of elastic vapours is a desideratum in Phy- 
sics. A knowledge of it is indispensable to an exact theory of 
the Steam Engine, to an exact theory of Astronomical Refrac- 
tions, and to an accurate solution of other important pro- 
blems. The want of it has hitherto been supplied by un- 
satisfactory approximations; but these questions cannot be 
completely investigated without a more careful attention to 
the premises than has hitherto been possible, owing to a want 
of the proper key to these researches, which consists in a know- 
ledge of the mathematical law which connects the tempera- 
ture and the pressure in elastic fluids, and which is required 
in addition to the law of Mariotte and Gay Lussac to com- 
plete their theory. 
If V represent the absolute heat or caloric^ i the latent 
heat, c the sensible heat or that which affects the thermometer.^ 
V= i + 6^. 
* Reprinted, by the obliging permission of the author, from the original me- 
moir lately published, London, 1840. 8vo. 
