Through August the Northbrook Public Library is devoting its weekly free film series to classic comedy shorts, and this well-chosen survey of Buster Keaton’s two-reelers, all shot between 1920 and ’22, 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 Boat (1921, 22 min.)—a dry run for his 1924 masterpiece The Navigator—he builds a sailboat inside his basement-level garage but discovers that it’s too wide to come out; when he hitches it to his car and tows it, the garage walls buckle and the entire house collapses. In The Blacksmith (1922, 21 min.), he removes a wheel from an auto and holds up the axle by attaching a child’s balloon; later a speeding locomotive comes to an abrupt halt inches from the trapped hero. And in Cops (1922, 18 min.), Keaton accidentally tosses an anarchist’s bomb into the reviewing stand at a parade (echoing a real-life terrorist attack on Wall Street two years earlier) and, in one of the silent cinema’s most enduring images, runs alone down the center of a city street pursued by hundreds of police. 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. Keaton’s nominal codirector on The Blacksmith was Mal St. Clair; on the other three, Eddie Cline.