I just finished another book about movie history: The Last Silent Picture Show: Silent Films on American Screens in the 1930s. It’s a surprising book if you take Singin’ in the Rain literally and assume that talkies supplanted silent movies overnight. Al Jolson notwithstanding, the studios weren’t willing to give up on their vast libraries of silents; they wanted to make money from them as long as they could, so they scored and added sound effects (but not dialogue) to some of their big hits and re-released them. Sometimes it worked. The Birth of a Nation, Ben Hur, and The Sheik, re-released with sound, pulled in audiences in the 30s.