Albert Einstein (2015). “Bite-Size Einstein: Quotations on Just About Everything from the Greatest Mind of the Twentieth Century”, p.32, St. Martin's Press
Michael Faraday (1842). “Chemical Manipulation: Being Instructions to Students in Chemistry on the Methods of Performing Experiments of Demonstration Or Research, with Accuracy and Success”, p.1
Michael Faraday's letter to John Tyndall (April 19, 1851) as quoted in "The correspondence of Michael Faraday", Volume 4, edited by Frank A. J. L. James, 1999.