 In 1920, first in a newspaper article (reprinted in Essays in Science and Philosophy), and then in a lecture (published as Chapter VIII of Concept of Nature), Whitehead made public an outline of his alternative to Einstein’s GTR. In 1921, Whitehead had the opportunity to discuss matters with Einstein himself. And finally, in 1922, Whitehead published a book with a more detailed account of his alternative theory of gravitation (ATG)—The Principle of Relativity.