In the spring of 1916, the University of Cambridge received a reprint of “The General Theory of Relativity” from Leiden, the Netherlands—a country of neutrality in the War. Foreign Member of the British Royal Astronomical Society, Dutch astronomer De Sitter (1872–1934) had just received the reprint from Einstein. De Sitter immediately put on stamps and mailed it to England. A perusal of Einstein’s new work convinced Professor Arthur Eddington (1882–1944), the Academic Secretary of the Society, what he held in hand was an unprecedented masterpiece. He began working on general relativity at once, and invited de Sitter to write three articles to introduce the theory. Published in the Proceedings of the Society, De Sitter’s introductory papers roused broad attention to and interest in general relativity in Britain. Since Englishman Isaac Newton discovered the law of universal gravitation two and one half centuries ago, it was the first serious challenge to Newton’s theory of gravity (Fig. 8.1).