"Finalist for the PROSE Award in History of Science, Medicine, and Technology, Association of American Publishers" "One of BBC Sky at Night Magazine's Best Astronomy and Space Books of 2019" "One of Nature's Top Ten Books of 2019" Daniel Kennefick is associate professor of physics at the University of Arkansas, Fayetteville. He is the author of Traveling at the Speed of Thought: Einstein and the Quest for Gravitational Waves and a coauthor of An Einstein Encyclopedia (both Princeton). On their 100th anniversary, the story of the extraordinary scientific expeditions that ushered in the era of relativity In 1919, British scientists led extraordinary expeditions to Brazil and Africa to test Albert Einstein's revolutionary new theory of general relativity in what became the century's most celebrated scientific experiment. The result ushered in a new era and made Einstein a global celebrity by confirming his dramatic prediction that the path of light rays would be bent by gravity. Today, Einstein's theory is scientific fact. Yet the effort to "weigh light" by measuring the gravitational deflection of starlight during the May 29, 1919, solar eclipse has become clouded by myth and skepticism. Could Arthur Eddington and Frank Dyson have gotten the results they claimed? Did the pacifist Eddington falsify evidence to foster peace after a horrific war by validating the theory of a German antiwar campaigner? In No Shadow of a Doubt, Daniel Kennefick provides definitive answers by offering the most comprehensive and authoritative account of how expedition scientists overcame war, bad weather, and equipment problems to make the experiment a triumphant success. The reader follows Eddington on his voyage to Africa through his letters home, and delves with Dyson into how the complex experiment was accomplished, through his notes. Other characters include Howard Grubb, the brilliant Irishman who made the instruments; William Campbell, the American astronomer who confirmed the result; and Erwin Findlay-Freundlich, the German whose attempts to perform the test in Crimea were foiled by clouds and his arrest. By chronicling the expeditions and their enormous impact in greater detail than ever before, No Shadow of a Doubt reveals a story that is even richer and more exciting than previously known. "[No Shadow of a Doubt] offers a richly detailed account of the protagonists and their success against long odds. Mr. Kennefick is at his most compelling when dissecting and refuting accusations of bias that have shrouded the historic feat."---Ray Jayawardhana, Wall Street Journal "Kennefick brings a thrilling mix of ingredients together into a . . . rewarding read: the chutzpah of Einstein; the glamour, luck and sense of adventure of eclipse-chasing; the audacity of planning such a demanding experiment during the first world war and executing it in its chaotic aftermath."---Anjana Ahuja, Financial Times "Physicist Kennefick narrates the buildup to, and fallout from, the experiment that confirmed Einstein's radical idea and made him an international star."---Andrea Gawrylewski, Scientific American "Meticulously researched and vividly written, [this] account is sure to become the standard reference work on this fascinating example of 'Big Science'."---Peter Coles, Nature "[An] insightful biography."---Simon Ings, The Spectator "This is a fascinating book, full of insights into the relationship between theory and experimental proof, and the relationship between science, internationalism, and war."---Emily Winterburn, BBC Sky at Night Magazine "A detailed and scholarly examination of the 1919 eclipse expeditions . . . a wonderfully rich and authoritative study of the way science worked in 1919 ("a golden age for astronomy")."---P. D. Smith, Times Literary Supplement "[Kennefick's] purpose is to very thoroughly rebut the skeptics, which he accomplishes in part through a careful and technical review of the instruments, the data, a