Two autograph letters signed from Robert Charles Winthrop to Charles Lyell and Mary Horner Lyell. Boston, 3 November 1849 and 1 May 1873. With portrait photograph by Warren's in Boston, mounted on cardboard carrier, signed.

1. In the first letter, dated 3 November 1849 and sent to Charles Lyell, Winthrop expresses delight at reading Lyell's "Second visit" and eagerly anticipates a potential "third visit." The letter acknowledges Lyell's positive allusions and playfully expresses concern that he may run out of compliments. This references Lyell's works, Travels in North America (1845) and Second visit to the United States of North America (1849), highlighting their nature as travel diaries from lecture tours in the U.S. and Canada between 1841 and 1853.

2. The second letter, dated 1 May 1873 and sent to Mary Horner Lyell, discusses a memorial and the financial challenges facing the Cambridge Museum. Winthrop, amid the "confusion of moving into [a] new town house", mentions sending names for the Sedgwick Memorial [referring to the British geologist Adam Sedgwick, who had died in January of the same year]. and the involvement of Louis Agassiz in seeking funding for the Cambridge Museum. The letter acknowledges Agassiz's disappointment over a legislative setback and highlights the financial strain on the museum. Winthrop also praises Mary's sisters for their work on "Walks in Florence" and shares condolences for the death of a mutual friend, Lord Ossington [i. e. the British statesman John Evelyn Denison, 1st Viscount of Ossington, the speaker of the House of Commons from 1857 to 1872], expressing sentiments about Ossington's distinguished career and his significance as an early English visitor to America.