THE MISSING REEL by Christopher Rawlence (Atheneum: $19.95; 306 pp.) . Louis Aime Augustin Le Prince has heretofore merited but a footnote in the history of film, often being cited as only one of many who participated in the invention of the movie camera. In this book Christopher Rawlence argues, successfully, that Le Prince's contributions have never received their due, and appears to solve the great mystery in Le Prince's life: his disappearance in 1890 while on the verge of going public with a working, single-lens movie camera. "The Missing Reel" is marred by too many shifts in time and perspective--Rawlence, a film maker, is better at writing scenes than providing narrative momentum--but this tale is a good one . . . especially because the bad guy is none other than Thomas Alva Edison, American hero, who wouldn't give credit to others when he could take it for himself.