Page 200 - 4670

for the remaining portion of the earth. While the observational
requirements for these computations appear enormous, the results well
justify the necessary survey work.

Figure 13.4 Products of the gravimetric method

Figure 13.4. shows how the mass surplus of the mountains and

the mass deficiency of the oceans cause the deflections of the vertical
and the undulations of the geoid. A mountain mass attracts the plumb
line from the normal of the ellipsoid. Likewise the mass deficiency of
the ocean does not attract the plumb line. These effects of the mass

anomalies contribute to the deflection of the vertical. However, both
deflections of the vertical and undulation values result from density
variations throughout the earth. In the area of mass surplus, the

observed gravity (reduced to sea level considering only the elevation)
is generally greater than the theoretical value, and the anomalies are
positive. In the areas of mass deficiency, the observed (reduced in the
same manner) is generally smaller than the theoretical value and the

anomalies are negative. Figure 13.5.
The deflections and undulations computed with sufficient gravity
information are considered absolue values referred to an earth-

200