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INTERNAL ENERGY. 
The energy of expansion of U x is to cover this rate, with 
the understanding that the conditions resulting after the change 
are a complete expression of the energy of cohesion in the 
matter present. For, with a new volume at U x a new con 
dition of equilibrium must exist between the half masses now 
acting. Under change the energy stored can be measured in 
the usual way. 
If the particles are not ionized, but remain neutral, no action 
occurs. Or again, if the particles are only slightly ionized, 
so that the reaction occurs slowly, the speed can be influenced 
by the presence of a third set of atoms. 
When the latter, under catalytic action, are able to induce 
locally greater compression, among the acting parts, the inter 
action of these pairs is stimulated. But, in uniting they bind 
only specific amounts of gravitational energy, which are en 
tirely dependent upon their own internal conditions. 
On this account they cannot detract in any way from the 
amount originally held by the third set of particles. These 
latter act then by their presence only, stimulating the rate of 
change. 
If under any of these conditions action does occur and an 
excess of energy is present over that required by the new pair, 
it is freed; or if sufficient energy, for the new condition, is not 
present a lowering of the temperature of the total mass indicates 
the shortage. 
The amount covering the actual cohesion present is still re 
tained, in the material, and it is just that amount we are seek 
ing to measure by the expansion of the material into volumes 
between fixed stations. 
At present we are unable to determine this expansion, or 
even the conditions of cohesion which it represents, except by 
the merest outline. We know that this force is related to the 
acting mass and to the form of the ultimate particle. 
This latter attribute determines the original distance apart 
of these particles, from which they must be driven by ex 
pansion to a neutral position under atmospheric pressure. 
Eventually, however, a law must be determinable from a 
knowledge of the heat energy conditioning the change, and of 
the stresses interacting in the half chemical masses. 
For the present we must be satisfied with a tentative deter