Geophysical Abstracts 152 January-March 1953

10 GEOPHYSICAL ABSTRACTS 152, JANUARY-MARCH 1953
Practical considerations of the making of such observations and their analysis
and interpretation are considered in this paper. M. C. R.
14194. Cizancourt, Henri de. Sur un mode de calcul des anomalies isostatiques
[On a method of calculating isostatic anomalies]: Acad. Sci. Paris
Comptes Rendus, tome 236, no. 8, p. 835-837,1953.
A method of calculating isostatic anomalies based on the balancing of vertical
tensions induced by topographic loads, in the hypothesis of relaxation, and the
thrust due to the deformation of the adjacent medium, is presented. It defines
the compensating masses without involving arbitrary coefficients and permits
studying the physical nature of isostatic equilibrium or lack of equilibrium.
Author's Abstract, M. O. R.
14195. Lopez Arroyo, Alfonso. Calculo de los errores cometidos en las reduc-
ciones topografica e isostatica [Calculation of the errors associated with
the determination of topographic and isostatic reductions]: Rev.
Geofiisica, v. 11, no. 42, p. 173-178,1952.
The three corrections applied to the gravity measurement when reducing it to
a geoid surface, the free air, topographic, and isostatic corrections, are discussed
and errors in their determination as affected by the procedure used, precision of
available maps, geologic data, results of surveying, and other auxiliary data are
analyzed. The precision of data necessary to attain the desired accuracy of
reductions is also analyzed. In calculating isostatic reductions, auxiliary graphs
are constructed to shorten the procedure. 8. T. V.
14196. Gel'fand, I. S. Pryamyye metody interpretatsii gravitatsionnykh i
magnitnykh anomality ot dvukhmernukh tel [Direct methods of inter­
pretation of gravitational and magnetic anomalies produced by two-
dimensional bodies]: Akad. Nauk SSSR, Ural'skiy filial, Trudy Gorno-
Geol. Inst., vypusk 19, Geofiz. sbornik 1, p. 51-63, 1950.
Formulas for direct interpretation of gravitational and magnetic anomalies,
which give the mass of the disturbing body, position of its center, and other
features, may be made more convenient for use by the simplification in the
computations of pertinent integrals introduced here. (See also Geophys. Abs.
14092). 8. T. V.
14197. Rice, Donald A. Deflections of the vertical from gravity anomalies:
Bull, geod., no. 25, p. 285-312,1952.
Results are reported of an investigation by the U. S. Coast and Geodetic
Survey of the accuracy with which deflections of the vertical can be obtained
from analysis of gravity variations throughout a somewhat limited area. Data
from about 40,000 gravity stations in an area of 800,000 sq mi were used. Agree­
ments of the order of 1 second were obtained between astronomic-geodetic and
gravimetric deflections using gravity fields limited to a radius of 150 km. In
extension of the radius to 500 or 600 km, the gravimetric deflection changed by
1 to 2 seconds and at 600 km the gravimetric deflections appeared to approach
absolute values within about 1 second. Residual differences are attributed to
lack of adequate data outside the central area. Assuming the validity of gravity
representation outside the central area, the latitude datum of the North Ameri­
can 1927 adjustment is about 1 second too large and the longitude datum is
within about 0.3 second of the absolute value. M. C. R.