I want to know the answer to the following question:
On what date did Delacroix write a letter based on his visit at Nohant?
All the background I'm provided with is that "During the summers at Nohant, particularly in the years 1839–43, Chopin found quiet, productive days during which he composed many works, including his Polonaise in A-flat major, Op.". Is that enough to answer the question?