I don't have anything on Nathaniel Burkett and Polly Hartman. However the book "Descendants of Jehu Burket (Burkhard) (1940 avail. thru the Family History Libary) mentions Nathaniel Burkett and Elizabeth Kessler's son Ephraim Burkett (b. 1825) marrying a Sarah Jane Hartman and having 5 children. Ephraim served in the Civil War. That's all I have.