 Mill joined the debate over scientific method which followed on from John Herschel's 1830 publication of "A Preliminary Discourse on the study of Natural Philosophy", which incorporated inductive reasoning from the known to the unknown, discovering general laws in specific facts and verifying these laws empirically.William Whewell expanded on this in his 1837 "History of the Inductive Sciences, from the Earliest to the Present Time", followed in 1840 by "The Philosophy of the Inductive Sciences, Founded Upon their History", presenting induction as the mind superimposing concepts on facts.Laws were self-evident truths, which could be known without need for empirical verification.