A new determination of the figure of the Earth from arcs

As part of a broader study on the figure of the Earth, a tentative size is derived based on four arcs: a meridional arc extending from South Africa to Scandinavia, a meridional arc extending from Chile to Canada, a parallel traversing the United States, and a parallel extending from western Europe to Siberia. The first two arcs were completed within the past three years and are the longest of their kind ever available—about 100° in length. The information they supply on the Earth's size is presented here for the first time. The data were applied in two forms: astrogeodetic (free‐air), and isostatically reduced deflections. The solutions assumed a flattening, ƒ = 1/(297 ± 1). The following values were obtained for the semi‐major axis a: free‐air, 6,378,240 ± 100 m; and isostatic, 6,378,285 db 100 m. As a single value, 6,378,260 =b 100 m can be taken. The uncertainty of a is due not only to the data, but also in large measure to the assumed uncertainty in ƒ, and to an uncertainty due to the systematic undulations of the geoid as given by Jeffreys.