Photographer August Sander's monumental "People of the Twentieth Century" series of portraits spanned the social classes in Weimar Germany: shoemaker, philosopher, farmer, aviator. Are their grim faces a foreshadowing of what lies ahead in the Nazi era? Adam Kirsch looks into their eyes and muses on these individuals and history in his new book "Emblems of the Passing World: Poems After Photographs by August Sander" . Each poem sits opposite one of Sander's images. The combination is penetrating. The fate of the individual in each photograph is unknown. In muscular yet wistful language, Kirsch leads each viewer to imagine it.