of Bodies from their Expansion. 253 
Granting that the principles I have assumed are correct, it 
appears that the expansion expresses the real quantity of heat 
necessary to produce a given change of temperature, and the ratio 
of the specific weights of the ultimate particles of bodies being 
known, the absolute quantity of heat in any body might be as- 
_ certained. 
If the expansion do not express the real quantity of heat, to 
what cause is the increase of bulk to be attributed? On the other 
hand, the experiments that have hitherto been instituted for the 
purpose of determining the specific heat of bodies, must be shown 
to be founded on erroneous principles, before the view of the sub- 
ject, now submitted, can be considered correct. To discuss this 
point, it will be necessary to consider the nature of the changes 
produced in bodies by the action of attraction or affinity. 
Solids and fluids, whenever they are exposed to gaseous bodies, 
always absorb a portion of them, and gaseous bodies absorb one 
another; in the same manner as heat is absorbed by all bodies. 
But the portion of gas absorbed varies, as the temperature; con- 
sequently a specific quantity of gas is essential to fluids and so- 
lids in their natural state. 
Now, unless the attraction between the particles of the body 
be less than its attraction for the particles of the one it absorbs, 
no chemical change will take place in the absorbent; but the ab- 
sorption will continue till the forces are in equilibrio. If the 
heterogeneous attraction exceed the homogeneous, then a new 
combination forms, and the bodies unite in definite proportions 3 
and whatever tends to lessen the homogeneous attraction facili- 
tates this change. _ 
Water is the body that has been generally used to obtain the 
specific heat of bodies: but water holds a considerable portion of 
gas in its pores, and the quantity appears to be inversely as the 
temperature. Hence it is that water has a maximum of density, 
which has been considered an anomaly in the law of expansion 
in consequence of having overlooked this circumstance. The 
absorption of gases by other fluids appears in like manner to be 
the cause of the irregularity of their expansion. 
The mean temperature of any mixture will be influenced by 
the same cause, and therefore the specific heats determined by 
such methods will be incorrect. 
If two portions of water of different temperatures be mixed, the 
temperature of the mixture will be nearly an arithmetical mean 
between those before mixture, because the specific gas is the 
same at all temperatures, in the same manner as the specific heat. 
But when any other body is mixed with water of a different tem- 
perature, the specific gas, as well as the specific heat, has an 
influence 
