The Absolute Determination of the Acceleration Due to Gravity

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Abstract
The place of absolute measurements of gravity in the system of fundamental constants of physics and celestial mechanics is discussed and the history of absolute determinations is summarised. Two classes of method are mainly used at present, the reversible pendulum and the free-motion experiment. The principles of these methods are discussed in detail, particular attention being given to the definition of experimental parameters and to perturbing effects. The results so far obtained are described and experiments still in progress are mentioned. Three of the completed determinations are in Europe - at Leningrad (reversible pendulum), Teddington (reversible pendulum) and at Sèvres (free-fall of line standard) and three are in N. America - at Washington (reversible pendulum), at Ottawa (free fall of graduated scale) and at Princeton (free fall of interferometer component). Comparisons between the results can only be made through measurements of the differences of gravity between the six sites and the problems of obtaining reliable differential results are indicated. It appears that the N. American results are more scattered than the European ones and that they differ from them by more than 2 mgal, an apparently significant amount. It is most likely that the differential measurements have systematic errors but there is a great need for further absolute measurements, especially in North America, to confirm or invalidate this conclusion.

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