Contains letters from contemporaries, colleagues, friends, and former students including: Carlos Paton Blacker, David Glass, Prof John MacMurray, Sir Thomson Buston Robson, Sir James Learmonth, Sir Edward Appleton, Sir Edmund Whittaker, and Professor Edwin Bidwell Wilson.

The letters recall Thomson's life and work, and what he meant to the sender. In many cases, the letters have annotations by Lady Thomson giving biographical information about the sender and their relationship to Thomson.

All letters are addressed to Lady Thomson, apart from one which is addressed to Hector Thomson.