6oo 
GEOPHYSICS: R. B. SOSMAN 
Proc. N. a. S. 
General Geophysics. — The physics of the earth considered as a unit 
(the classical "geophysics") is for the most part either covered by other 
Sections of the Geophysical Union or is customarily considered as a part 
of geology. Certain phases of geophysics, however, are not thus assign- 
able and may be mentioned here in order that all of the groups of prob- 
lems of the science may receive attention in this assembly of surveys. 
The form and gravitation relations of our suspended spheroid, its mag- 
netic and electrical properties, its properties as a vibrating body, and the 
physics of its air and water envelopes, are the obvious fields of appropriate 
Sections. Hypotheses of its origin and the logical deductions therefrom 
may confidently be left to the geologists, among whose faults that of nar- 
row-mindedness and lack of a broad outlook in time and space have 
seldom been numbered.^ Its properties as an absorbing and reflecting 
body for external radiation are being well handled by the astrophysicists 
and meteorologists. 
The problem of the earth as a body radiating its own heat into space, 
however, is an example of a problem that may fail of treatment as a unit 
problem by any one of the above-mentioned groups acting alone. We 
are dealing not with a solid homogeneous spheroid of uniform surface 
temperature radiating freely into space, but with a rather heterogeneous 
body blanketed with several kinds of heat insulators whose composition 
varies both with depth and with time. Factors in the problem are: the 
production of heat by shrinkage; the contributions of heat from radio- 
active sources; the earth's present thermal conductivity and thermal 
gradient; the effect of varying carbon dioxide, water, ozone, inorganic 
dust, and clouds, upon the heat loss; and the effects of the possibly very 
different atmospheres with which the earth has been blanketed in past 
ages. The temperature at a given time and at a given distance from 
the center, as for instance at the solid surface of the land, depends upon 
a complex set of factors, and may well have been periodic in its varia- 
tions. 
The earth's volume and shape may have been similarly variable. In 
addition to the variation of temperature, already mentioned, the follow- 
ing are among the factors to be considered : the tides in the solid earth (on 
which extensive experimental work has recently been in progress) and the 
earth's properties as an elastic body; the viscosity of the earth as a whole, 
with relation to long-continued forces, and the existing state and method 
of maintenance of isostatic equilibrium in its surface layer; its breaking 
strength and form of rupture under forces changing too rapidly to cause 
flow; and the lag of elastic and viscous responses to changing forces, as 
in the case of the addition or removal of continental ice sheets. 
Limitations of space forbid more than a sketchy outline of the problems 
set before the Section of Geophysical-chemistry, but it is hoped that the 
