Through August the Northbrook Public Library is devoting its weekly free film series to classic silent comedies, and this well-chosen survey of Buster Keaton's two-reelers, all shot between 1920 and '22 by Keaton and Eddie Cline, provides a striking glimpse of a cinematic genius as he masters his craft, develops his stoic screen persona, and toys with some of the themes that would later blossom in his features. Yet Keaton's shorts, free of the plot and character development demanded by longer films, have a lunatic energy and surreal vision all their own. In One Week (1920, 19 min.) Keaton struggles to assemble a prefabricated house, and the result is a cubist nightmare that alone explains his work's importance to Salvador Dali, Samuel Beckett, and Luis Buñuel. In The Frozen North (1922, 17 min.) he boards a New York subway train that deposits him in the middle of the arctic. And at the end of The Electric House (1922, 25 min.) a ghostly Keaton climbs a stairway to heaven, but after Saint Peter rejects him it turns into a slide and sends him plunging to the opposite destination. Even in the age of digital effects and nine-figure budgets, the sight gags in these rudimentary two-reelers still hold up, astonishing in their geometric precision and graceful execution. On the same program, My Wife's Relations (1922, 30 min.) and one ringer: Fatty Arbuckle's Coney Island (1917, 34 min.), with Keaton in a supporting role.