Geophysical Surveys and their Utilization

Abstract

AT the Newcastle meeting of the British Association, a discussion on geophysics was held by Section A (Mathematics and Physics), under the chairmanship of Sir Harold Spencer Jones. Mr. B. C. Browne opened the discussion with an account of gravity survey in the British Isles. The acceleration due to gravity is almost the same at all points on the surface of the earth, but accurate measurements show that the value at the equator is about a half per cent less than at the poles. The normal value at any particular latitude is usually assumed to be that given by the international gravity formula. In the British Isles, the mean variation is approximately 1·3 milligals (1·3 X 10^-3 cm./sec.²) per mile. Superimposed on this are local variations arising from changes in height and the attraction of topographic features such as mountains and seas. After allowing for the effect of elevation and topography, the difference between the observed value of gravity and the value given by the international gravity formula is known as the Bouguer anomaly. This represents the attraction of the anomalous masses present within the earth.