JOURNAL 
OF THE 
WASHINGTON ACADEMY OF SCIENCES 
Vou. 13 NovEMBER 19, 1923 No. 19 
GEOPHYSICS.—Density distribution in the Earth. EK. D. Wi1LutAM- 
son and L. H. Apams, Geophysical Laboratory, Carnegie Insti- 
tution of Washington. 
There are four principal sources of information concerning the 
interior of the Earth: (1) the constant of gravitation, from which 
the total mass and average density of the Earth are determined; 
(2) the constant of precession and other astronomic and geodetic data 
from which the moments of inertia of the Earth may be calculated, 
the moment of inertia allowing important inferences to be drawn 
concerning the density distribution within the Earth; (3) seismologic 
data from which the elastic constants of the materials in the interior 
may be computed; and (4) the known flattening of the Earth as 
determined from the data of geodesy with which any assumed dis- 
tribution of materials must harmonize. The first three of these 
sources, together with the values of the elastic constants of various 
rocks previously obtained by the authors,’ provide the basis for the 
present estimate of the density and composition of the Earth at 
various depths. The bearing of the above classes of data on the 
constitution of the Earth’s interior will first be discussed briefly. 
Mean density of the Earth. The constant of gravitation from direct 
experimental observation is known to be 6.66 X 10-* cm'/g-sec’. 
This fixes the average density of the Earth at 5.52, and, as is well 
known, this fact alone allows certain qualitative inferences to be 
drawn concerning the interior. The density of any ordinary rock is 
much less than 5.52; therefore in all probability the density near the 
center must be considerably higher than 5.52 in order to bring the 
1 Received October 19, 1923. 
2 Journ. Franklin Inst. 195: 475-529. 19253. 
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