At once sophisticated and absurd, the slapstick comedy of silent-film star Keaton lights up the Harvard Film Archive tonight in a screening of 1923's The Balloonatic and 1924's Sherlock Jr. The former finds Keaton stranded in the wilderness, where he encounters a young woman (Phyllis Haver) camping nearby; the latter is a tale of a lovesick projectionist who dreams himself into the movie he is playing.