Thought this shouldn't go unnoticed: http://www.loc.gov/bookfest/books-that-shaped-america/

The Library of Congress, the world’s largest repository of knowledge and information, began a multiyear “Celebration of the Book” with an exhibition on “Books That Shaped America.” The initial books in the exhibition are displayed below.

“This list is a starting point,” said Librarian of Congress James H. Billington. “It is not a register of the ‘best’ American books – although many of them fit that description. Rather, the list is intended to spark a national conversation on books written by Americans that have influenced our lives, whether they appear on this initial list or not.”

...some of what the man did when he wasn't contemplating stone cutters' PTR.

He must have had quite the eye for detail. While the quote we love to embrace is primarily about persistence, I suspect Riis also took note of the subtleties of the act: the point of contact, angle of the chisel, force of the strike, etc. ...what we would probably call "the inner game."