A fragment of Letts's Diary, No. 13, 1873, mainly used by John Thomas to record his stay in St. Petersburg, December 1873-March 1874, and including references to concert arrangements and to meetings with the Duke of Edinburgh and with members of the Russian royal family and aristocracy.

A journal of a tour in Germany and Russia, 22 September 1852-13 April 1853, undertaken by John Thomas, including accounts of concerts given by him in St Petersburg, 1852-1853, and Moscow, 1853.