How did John Stuart Mill help Thomas Carlyle research The French Revolution?

John Stuart Mill assisted Thomas Carlyle with his work on The French Revolution by providing him with a significant amount of source material. Mill had been collecting these documents with the intention of potentially writing a volume on the subject himself, but he was willing to let Carlyle take on the project and frequently discussed the work's progress with him.1

The collaboration is also famously associated with a major setback: in 1835, Carlyle lent a substantial portion of his manuscript to Mill, who accidentally allowed it to be destroyed by fire. Despite the loss of months of work, Carlyle responded to the incident with remarkable generosity and forbearance, eventually rewriting the entire text to complete the book by 1837.21