Helge Kragh, Emeritus Professor, Niels Bohr Institute, University of Copenhagen, Denmark, Malcolm Longair, Director of Development and Outreach, Jacksonian Professor Emeritus of Natural Philosophy, Cavendish Laboratory Helge Kragh gained doctoral degrees in physics (1981) and in philosophy (2007). He was a high school teacher in physics and chemistry (1970- 87), and then later a professor of history of science at Cornell University, USA; University of Oslo, Norway; and University of Aarhus, Denmark (1987-2015). After retiring, he is now emeritus professor at the Niels Bohr Institute, University of Copenhagen, Denmark. Malcolm Longair is Director of Development and Outreach, Jacksonian Professor Emeritus of Natural Philosophy at the Cavendish Laboratory, University of Cambridge, UK. He also holds the position of Editor-in-Chief of the Biographical Memoirs of Fellows of the Royal Society (2016-2020). Longair has previously held positions as a university lecturer in the Department of Physics, University of Cambridge (1970--80); Astronomer Royal for Scotland, Regius Professor of Astronomy, University of Edinburgh, Director of the Royal Observatory, Edinburgh (1980--90); Jacksonian Professor of Natural Philosophy, University of Cambridge (1991--2008); and Head of Cavendish Laboratory (1997--2005).