Published online by Cambridge University Press: 18 January 2010
The aim of the Duke of Edinburgh's Lectures is ‘to extend the horizons of navigational interest’. I have been able to interpret this literally, for if you extend these horizons far enough, what do you arrive at but the subject of this lecture, the shape of the Earth? It is a subject which has been revolutionized in the past five years by analysis of the orbits of artificial satellites: the two years from 1958 to 1960 saw more progress than the previous 200 years, and since 1960 the pace of progress has shown no sign of slackening.