J. L. Heilbron is a professor of history and Vice Chancellor Emeritus, University of California at Berkeley, and currently Senior Research Fellow, Worcester College, Oxford. He is the author of numerous books on the history of science, including most recentlyThe Sun in the Church: Cathedrals as Solar ObservatoriesandGeometry Civilized: History, Culture, and Technique. Stephen Jay Gould is the Alexander Agassiz professor of zoology and professor of geology at Harvard and the Vincent Astor visiting professor of biology at New York University. Recent books includeFull House,Dinosaur in a Haystack, andQuestioning the Millennium. He lives in Cambridge, Massachusetts, and New York City.