462 Analyses of Books. [JuNE, 
action. It is obvious that heat ought to be better reflected by 
the surfaces which have a metallic lustre than by those whi 
want that lustre; because this lustre indicates that the surface 
has little inequality, especially in the smallest parts. But we 
know likewise that the forces of which we are treating are 
transmitted more easily by means of points elevated above a 
surface than by those that form a level surface. Hence we see 
that bodies with a brilliant surface ought not merely to reflect 
more perfectly the external heat which endeavours to penetrate 
-into them, but likewise the internal heat which endeavours to 
escape, as has been proved by the beautiful experiments of 
Leshe and Rumford. According to our principles, those bodies 
which are the least capable of conducting a great quantity of 
electric forces are the most proper to transmit this calorific 
action; for they are most proper for its production, and its 
propagation is merely a continued production. The small 
number of experiments to which we can at present apply this 
principle confirm it ; especially the great facility which we find 
in all the gases for this sort of transmission. It would be requi- 
site to ascertain whether the oils do not possess the same 
property in a higher degree than all other liquids.” 
_ The opposite forces in bodies are disturbed by friction. If one 
of these forces be permitted to make its escape by opening a 
communication with the earth, we have the phenomena of elec- 
tricity ; but when this separation does not take place, nothing 
takes place but an internal change im the equilibrium ; and in 
consequence, the different phenomena of heat. Prof. CErsted 
then shows at considerable length that the evolution of heat by 
friction is inconsistent with the common theory which supposes 
a calorific matter; but that it is perfectly consistent with his 
own theory that heat is the consequence of the union of the two 
electricities in particular circumstances. 
The quantity of the opposite forces which exists in each body 
appears then to be very great. The chemical properties of the 
body depend upon the preponderating force ; but the preponde- 
rating quantity must, in all cases, be very small, when compared 
with that of the forces which are in equilibrio. The dilatation 
of bodies is not owing to the preponderating force, but to the 
expansive property of those forces which are in equilibrium, and 
which produce a dilatation which is greater or less according to 
the intimacy of their combinations ; for a body occupies the less 
volume the more intimately its forces are united, and is the more 
dilated the less intimately they are united. Hence a hot body in 
which the equilibrium of the forces is more disturbed ought to be 
more dilated than a cold body in which the equilibrium is more 
intimate. 
The remainder of this chapter is taken up by our author in 
showing that all the facts respecting heat with which we are 
acquainted follow naturally as consequences from his theory. 
These facts are chiefly the following : 1. That all bodies contam 
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