Michael Faraday, Christian Friedirich Schoenbein (1899). “The letters of Faraday and Schoenbein 1836-1862: With notes, comments and references to contemporary letters”
George Santayana, Marianne S. Wokeck, Martin A. Coleman, James Gouinlock (2013). “The Life of Reason or The Phases of Human Progress: Reason in Society, Volume VII, Book Two”, p.27, MIT Press