On the Twain essay on  Lincoln,  so thoughtfully provided by Barb Schmidt: I
don't know for sure, but I wouldguess thatClemens wrote it as afavor to Henry
Watterson, notable newspaper editor, cousin of Clemens and long-time friend.
They saw one another infrequently and communicated irregularly, but were still
quite close. Watterson is listed as one of the Lincoln Birthplace Board members
           Andy Hoffman