 The other plausible methodological source for Darwin’s mature reasoning was the work of his older contemporary and former Cambridge mentor, the Rev. William Whewell (1794–1866), whose three-volume History of the Inductive Sciences (1837) Darwin read with care after his return from his round-the-world voyage. Again, the impact of Whewell’s explicit theory of scientific method, as set forth in his Philosophy of Inductive Science (first ed. 1840) in the pre-Origin period is difficult to document, with no direct evidence of the reading of Whewell’s Philosophy in the Darwin reading Notebooks or Correspondence from his formative years before the publication of the Origin.