This ninth volume of the Tyndall correspondence covers the period from February 1, 1865, to November 29, 1866. Tyndall was by now in his mid-forties and in the prime of life. His career as a man of science was firmly established and flourishing. He had been professor of natural philosophy at the Royal Institution for more than a dozen years and established himself as Michael Faraday’s successor. This volume also covers the period of Faraday’s increasing illness and withdrawal from public life, which had a significant impact on Tyndall both personally and in terms of his standing in the scientific world.