## Abstract

The theory of the application of gravity measurements to geodetic calculations is discussed, and the errors involved in calculating deflexions of the vertical are estimated. If the gravity data are given as free air anomalies from Jeffreys's (1948) formula, so that the second and third harmonics of gravity are assumed known, the orders of magnitude of the standard deviations of the different sources of error are the following: $ \matrix\format\l\kern.8em&\l \\ \text{Single deflexion}\colon \text{neglect of gravity outside}\ 20^{\circ} & 1^{\prime \prime} \\ \text{Difference of deflexions}\colon \text{neglect of gravity outside}\ 5^{\circ} & 0^{\prime \prime}\cdot 5 \\ \text{Calculation of effects of gravity from}\ 0^{\circ}\cdot 05\ \text{to}\ 5^{\circ} & 0^{\prime \prime}\cdot 1 \\ \text{Calculation of effects of gravity within}\ 0^{\circ}\cdot 05 & \text{between}\ 0^{\prime \prime}\cdot 1\ \text{and}\ 0^{\prime \prime}\cdot 5 \endmatrix $ Estimates of the deflexions are made for Greenwich, Herstmonceux, Southampton and Bayeux, and the difference between Greenwich and Southampton is compared with the astronomical and geodetic amplitudes.