The collection includes Kelvin material formerly held at Add. 7618, and items of correspondence formerly held as Add. 2766 (4) 1-66. As with the Stokes Collection (Add. 7656), there are separate sections for correspondence, papers, and notebooks. The main correspondence sequence is particularly extensive, including letters from family, friends, and many important scientists of his day. Among Kelvin's more frequent correspondents are Hugh Blackburn, Arthur Cayley, Charles John Clay, George Howard Darwin, James Dewar, James David Forbes, James Prescott Joule, Joseph Larmor, Oliver Joseph Lodge, Joseph Henry McClure, James Clerk Maxwell, David Reid, John Rennie, Archibald Smith, George Gabriel Stokes, and Peter Guthrie Tait.