202 Dr. Woods’s Remarks on 
But M’m is the attraction which the hollow spheroid exerts on 
any point within it, and aw? is the centrifugal force at the axis of 
symmetry of the fluid mass. Whence we find that at the centre of 
the fluid mass the acting forces counterbalance each other, which 
might have been anticipated from a known theorem in mechanics. 
Gothenburgh, January 7, 1861. 
XXXI. Remarks on Sainte-Claire Deville’s Theory of Dissocia- 
tion. By Tuomas Woops, M.D. 
To the Editors of the Philosophical Magazine and Journal. 
GENTLEMEN, Parsonstown, February 1861. 
N an interesting paper by Sainte-Claire Deville published in 
this Magazine last December, that author gives his views on 
the decomposition of bodies by heat. His idea of the relation 
and behaviour of the constituents forming a compound, towards 
each other, is, physically considered, the same as that which I 
published in this Journal so long ago as January 1852; that is, 
that they act merely as the molecules of a simple body, differing 
in nothing from the latter, except that, beimg diverse, they 
are capable of attaining a greater proximity among themselves, 
and so of causing a greater opposite movement in the particles 
of other bodies. A reference to my paper will show a diagram 
I gave in order to explain this similarity of constitution. The 
paper was therefore the more interesting to me as it brings for- 
ward fresh ideas on a thought-of subject. As Ido not, how- 
ever, yet agree with what is new in it, I beg to offer a few 
remarks on some of its contents; and first with respect to his 
theory of dissociation. 
Sainte-Claire Deville thinks that compound gases and vapours, 
when heated to a certain temperature, as steam at 1000°, undergo 
some such change as a solid body does when it liquefies; that 
the constituent particles being removed from each other, as well 
as the compound particles, the gas loses stability, and that heat 
is rendered latent thereby. This condition he calls the disso- 
ciated state. I do not find he offers any demonstration of this 
state, but that he only ascribes to its influence the production 
of some phenomena previously otherwise explained. For instance, 
to account for the heat of chemical combination, he takes for 
granted, as an example, that the molecules of chlorine and 
hydrogen are double, and, even at low temperatures, in the disso- 
ciated state; and then ascribes the heat produced by their union 
to the latent heat of this particular condition, which he imagines 
is given out when the gases by their combination get ito a state 
of stability. 
Now, if the heat produced in this instance is due to the change 
