The 500 letters in this sixteenth volume of The Correspondence of John Tyndall document the period from January 1, 1878, to December 31, 1881. They chart a defining stage in the later life and career of an aging John Tyndall with unprecedented detail. Key developments evidence the fragility of a self-fashioned Carlylean hero, one whose sustenance increasingly relied on the companionate, domestic partnership that he enjoyed with his wife, Louisa. While they vacationed in the new summer home they built together in the Swiss Alps, where they experienced a shared reverence for nature, Louisa immersed herself daily in the business of Tyndall’s scientific work, directly assisting with experiments like the action of freshly fallen snow on the transmission of sound. But his failing bodily health—cascades of sickness, chronic insomnia above all else—disturbed his daily labours, transforming routine tasks into exhausting slogs. He also feared that growing forces of disorder—in his native Ireland most distressingly—threatened political, social, and economic stability.