The 308 letters in this volume cover a critical period in Tyndall’s personal and scientific lives. The volume begins with the difficult ending of his relationship with the Drummond family, disputes about his work in glaciology, and his early seminal work on the absorption of radiant heat by gases. It ends with the start of his championship of Julius Robert Mayer’s work on the mechanical equivalent of heat. In between, Tyndall carefully establishes his own priority for his work on radiant heat, and he accepts the position of professor of physics at the Government School of Mines. The lure of the Alps also becomes ever stronger. In this period comes perhaps Tyndall’s greatest mountaineering achievement, the first ascent of the Weisshorn, and a remarkable winter visit to Chamonix and the Mer de Glace. As his reputation grows, Tyndall continues to make his way in society. He is elected to the elite Athenaeum Club on January 31, 1860.