RECENT PROGRESS IN GEODESY.* 
BY 
Erasmus Darwin Preston. 
[Read before the Society April 30, 1898.] 
I. The Measurement of the Earth. 
Whatever may be the finally adopted size and shape of 
the earth, we are now in a position to modify materially 
some generally accepted notions in regard to it. During the 
course of this paper some recent facts bearing on the shape 
of the geoid will be brought forward, and it will be shown 
that a new theory of the earth’s collapse is thereby strength¬ 
ened. For more than twenty years the argument for a solid 
earth, deduced from the phenomena of precession and nu¬ 
tation, has been abandoned. Astronomers and Geologists 
are now agreed as to the plasticity of at least a thin shell 
next below the external rocks. This being admitted, the 
form assumed by the earth’s shrinking envelope becomes a 
matter of study, and all observations bearing on this point 
should receive their due share of consideration. It is for 
this purpose that attention is now called to three arcs—two 
in Europe and one in the United States—that have been 
measured parallel to the equator in quite recent times. In 
order to fully realize the gigantic strides made since the 
figure of the earth first became a subject of inquiry, let us 
look for a moment at the different steps in the process. Let 
us see how the human mind, first groping in the dark and 
trying to reconcile preconceived ideas with natural appear- 
* Published by permission of the Superintendent of the United States 
Coast and Geodetic Survey. 
37—Bull. Phil. Soc., Wash., Vol. 13. 
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