This is the book that inspired the song.  Read more about it here: Dear Sister: A Song 200 Years in the Making

Picked up the Dear Sister book again today to re-read part of it at random.  Once again I am impressed by the matter of fact way the brothers, particularly Lewis, approach their situations.  Hopeful, yet realistic.  And, the family distance and absence....  In a day when we can communicate almost instantly, their monthly letter arrivals are both painful and great emotional food.  It really is a good book.  Thanks again, Bill Bailey.