Albert Einstein (2015). “Bite-Size Einstein: Quotations on Just About Everything from the Greatest Mind of the Twentieth Century”, p.25, St. Martin's Press
"Fragments of a Poetics of Fire (A Retrospective Glance at the Lifework of a Master of Books)". Book by Gaston Bachelard edited by Suzanne Bachelard, 1988.
William Lyon Phelps (2016). “A Collection of Classic Essays by William Lyon Phelps - Including 'Happiness', 'Superstition', 'The Great American Game', and Many More”, p.106, Read Books Ltd
Albert Einstein (2015). “Bite-Size Einstein: Quotations on Just About Everything from the Greatest Mind of the Twentieth Century”, p.24, St. Martin's Press