694. T. C CHAMBERLIN 
vibratory and the minutely revolutional phases of energy. These 
speculative suggestions have little value beyond helping to make 
it clear that it is by no means safe to assume that atomic con- 
struction and destruction are not common functions of the interior. 
WHAT AMOUNT OF COMPRESSION IS IMPLIED BY THE MEAN DENSITY 
OF THE EARTH ? 
As already noted, there is no need to push appeal to the organiz- 
ing functions of energy in the interior so far as to assume the building 
up of atoms for the sake of explaining the higher density of the 
earth’s interior; indeed, if there is any constructive work of that 
sort, the increase above the decrease of density cannot go very 
far without making the mean density too great to fit the evidence. 
If we assume that the primitive matter had the meteoric density 
of 3.69 adopted by Farrington, and compare this with 5.53, the 
mean density of the earth adopted by Moulton, the mean increase 
in density due to compacting, reorganization, atomic change, etc., 
is only about 50 per cent. Or if, to assume an improbably low 
figure for the density of the earth’s original matter, we take the 
moon’s mean density, 3.34—assuming that the effects of com- 
pression at the moon’s center are offset by the porosity of its outer 
part—the increase in the earth’s mean density would be only a 
little over 65 per cent. In either case, or on any plausible assump- 
tion, some part of the compacting must be assigned to mechanical 
compression, so that the increase of density assignable to reorganiza- 
tion under the special conditions of the interior is not very large. 
THE INTIMATIONS OF THE DENSITY GRADIENT IN THE ZONE OF 
OBSERVATION 
Geologists have been at great labor to compile thermal data 
from mines and deep borings that they might deduce from these a 
temperature gradient that would throw light on interior conditions, 
but the same line of attack on the rising density of the interior 
seems to have been overlooked. It is to be recognized, of course, 
that neither of these gradients can be projected to the center of the 
earth without reservation, for both curves probably fall off notably 
in the interior, but the density curve is probably as trustworthy a 
