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Since the very early history of gravity measurements. the relation of gravity to the shape of the earlh and the nature of the earth's crust has been the subject of extensive studies. The variation of gravity with latitude was first noted when pendulum clocks were moved over great distances and their rates found to change. This. of course, results from the variation of gravity with latitude which comes about because of the combination of the effects due to the outward acceleration of the rotating earth and the consequent bulging at the equator and flattening at the poles. The shape of the earth is approximately that of a rotating liquid with a balance between its gravitational attraction on itself, which would make it a perfect sphere, and the centrifugal force due to the rotation which makes the sphere oblate. These relations have been defined by many observations of gravitv over the earth and geodetic analysis to give several formulas for the variation of gravity from the equator to the pole. The 1930 “international formula,” now generally accepted is

γ = 978.049(1 + 0.0052884sin2φ - 0.0000059sin22φ).

This gives γ, the gravity at sea level, as a function of the latitude φ Detailed tables of values of gravity from the equator to the poles are available.

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