Dated on the basis that 1842 was the only year in which Faraday delivered a Friday Evening Discourse on 15 April. See Lit.Gaz., 23 April 1842, p.279 for an account of this Discourse "On conduction in lightning-rods". The Athenaeum, 12 March 1842, p.235 had announced this lecture for 18 March 1842, which implies that Faraday cancelled what would have been his first Friday Evening Discourse for nearly two years.