In the earlier geophysical literature, many schemes were published for the calculation of gravity and magnetic effects. For the most part these were either the curves for the effects of certain definite geometric bodies or various charts and diagrams by which the effects for a body of any shape could be determined graphically. It is probable that these schemes have had comparatively little actual application in the interpretation of magnetic and gravity surveys. This is because of the fact that unless certain controls other than the gravity and magnetic data are available the inherent ambiguities of the physically possible distributions of material which can produce the observed effects make an accurate calculation meaningless, even though the geophysical data may be of any desired precision. Furthermore, it is often possible to calculate, from rather generalized forms, geophysical effects which are in agreement with those observed within the precision of the observations. In fact, unless two conditions are fulfilled, i.e., (1) observed data are of high precision and spaced at distances substantially less than the horizontal dimensions or depth of the disturbing body, and (2) some other control is available, there is little point to using any of the more refined methods of calculation.

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