Comparison of the acceleration due to gravity at the National Laboratory, Teddington and the Bureau of Standards, Washington, D. C

For many years values of gravity all over the world have been obtained relative to that at Potsdam by observations with invariable pendulums. The value at Potsdam was determined by Kühnen and Furtwängler (1906) by Kater’s method and a standard error of 0.003 cm./sec.2 was claimed for the result. Any error in the Potsdam value would involve an equal error in the related values all over the world. As the acceleration of gravity is involved in all measurements of force with the balance and thus in the unit of electric current and in such quantities as the velocity of anα -particle, it is important to know whether the accepted value at Potsdam has the accuracy claimed for it. A recent absolute determination by Heyl and Cook (1936) at the National Bureau of Standards, Washington, D.C., gave a result 0.020 cm./sec.2 less than that obtained by comparison with Potsdam, whilst one by Clark at the National Physical Laboratory, Teddington gave 0.0138 cm./sec.2 less. The relative gravity connexion between Potsdam and Washington is strong, but those between Teddington and Washington and between Teddington and Potsdam are weak and indirect. Advantage has therefore been taken of the visit of the authors to Washington to attend the recent meeting of the International Union of Geodesy and Geophysics to make a comparison of the values ofg at the places used for the absolute determinations at the National Physical Laboratory and at the National Bureau of Standards. It had been intended also to connect the National Physical Laboratory directly with Potsdam, but the outbreak of war has made it necessary for this to be postponed.