Liên kết ngoài
 Frugé, August. A Skeptic Among Scholars: August Frugé on University Publishing. Berkeley: University of California Press, c1993 1993. 
 California Digital Library (CDL) – University of California Libraries
 Free Online - UC Press E-Books Collection
 Mark Twain Project Online
 "Mark Twain's Biography Flying Off the Shelves", The New York Times, Nov. 19, 2010