This series consists of letters sent by Traubel to Sixsmith over a seventeen-year period, although they predominantly date from 1892-4. Traubel seems to have begun writing to Sixsmith after hearing of his interest in Whitman from Wallace.
These letters are different in tone from those sent to Wallace and Johnston. When writing to the young Sixsmith, Traubel seems to have cast himself in the role of spiritual advisor and interpreter of Whitman's message. He writes emotionally about visionary concept of brotherhood in Whitman's work, emphasising the 'adhesive love of comrades'. On his side, Sixsmith seems to have looked up to Traubel with great admiration: Traubel felt it necessary to remind him that he was simply an individual working to further the Whitman cause.
Sixsmith, however, developed his own ideas about Whitman's message of freedom and democracy, and his views reflect the differing interpretations placed upon Whitman's work by Traubel and the British Whitmanites: Sixsmith (along with many members of the Bolton group) was a socialist and believed Whitman's ideals could be achieved through the socialist movement, whereas Traubel advocated a much wider, all-embracing spiritual brotherhood.
There is a gap of 18 months in the correspondence following Traubel's letter of 23 July 1894 (Eng 1172/4/41), which is unusually terse in tone, and is a response to Sixsmith's criticisms of the International Whitman Fellowship which Traubel was trying to establish. The Bolton group wished to be affiliated to this movement but under their own terms, and they apparently disagreed with the formal organisation and subscription fees required.
The correspondence between Traubel and Sixsmith never seems to have returned to its early intimacy after this date, and the subsequent letters are much fewer in number, with a gap of 16 years from 1896 to 1912.