An extraordinary special section introduces four very different but equally gifted photographers—all of them discovered through persistent recent detective work. Here are crystalline scenes of New Yorkers getting on with their lives in the prosperous 1920s and the straitened 1930s; a bleak stereo view showing the bone-strewn ground of the Little Bighorn, which led to the identifying of a major Western cameraman; placid, sunny views of the gentry at play that conceal a tragedy that would kill thousands; and West Coast Civil War images that the government did everything in its power to keep you from seeing.