68 letters, mostly from Kelvin to his sister Elizabeth; a few to David King; some from Margaret Thomson, Kelvin's first wife, and Frances Thomson, his second wife; 3 from Charles and Margaret Watson at the time of Margaret Thomson's death; and 4 from Frances Thomson to Elizabeth, daughter of David and Elizabeth King. The letters cover family news; occasional references to Kelvin's scientific work; the long illness of Margaret Thomson, and of David King; the laying of Atlantic telegraph cables, 1865-1866, and other underwater cables; and the death at sea of David King junior, 1874. The collection also contains photographs, including one of a drawing of Lord Kelvin, his brother James Thomson and Elizabeth King, by Agnes Gardner King, and two photographs of Dr David King. The letters are from Lord Kelvin to Elizabeth Thomson unless stated.