REVIEWS 
Geodetic Operations in the United States 1903-1906. A Report to the 
Fifteenth General Conference of the International Geodetic 
Association. By O. H. Tirrmann and J. H. Havrorp. 
Washington, 1906. Pp. 45. 
While this paper embraces, as indicated, a statement of the principal 
operations of the Coast and Geodetic Survey for 1903-6, its chief contri- 
bution zelates to the figure of the earth. The part of special interest to 
geologists is that which deals with the relation of variations of density 
in the outer part of the lithosphere to the great surface reliefs. The 
investigation bearing upon this point was based wholly on the deflections 
of the vertical, no use being made of determinations of force of gravity. 
The area treated extends over 18° 51’ in latitude and 50° 7’ in longitude. 
Astronomic determinations of the deflection of the vertical to the number 
of 507, all connected by continuous primary triangulation, were used. 
It has long been known that the force of gravity on the surface of the 
earth is not distributed as though the sub-surface material were either 
homogeneous, gravitatively, or symmetrical. The investigation set forth 
in this paper, while fully confirming this, goes much beyond any previous 
inquiry in determining the nature of the inequalities in the distribution 
of gravity and their correlation with topography. It thus constitutes a 
very notable advance in this important line of research. The deflections 
of the vertical that are assignable to variations in the topography, con- 
sidered by itself alone, were first determined in a very comprehensive 
way, the effect of the reliefs within a radius of 4126.4 kilometers being 
computed for each station. The results clearly indicated that the material 
of the protuberances, viewed largely, has less inherent gravity than that 
of the basins—a conclusion in accord with the general tenor of previous 
inquiries in different periods of the world. It remained therefore to deter- 
mine the distribution of the internal inequalities of density thus disclosed. 
The essential feature of the problem was to find out whether the differ- 
ences of density are so distributed that the continental and oceanic columns 
balance one another or not, and, if they do, at what depth the equation is 
established. A series of hypotheses relative to this were adopted as the 
bases of trial solutions. While these hypotheses, so far as they enter 
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