Susan Howe's newest book of poetry is a revelation as well as a mystery."What treasures of knowledge we cluster around."That Thisis a collection in three pieces. "Disappearance Approach," an essay about the sudden death of the author's husband ("land of darkness or darkness itself you shadow mouth"), begins the book with paintings by Poussin, an autopsy, Sarah Edwards and her sister-in-law Hannah, phantoms, elusive remnants, and snakes. "Frolic Architecture," the second section — inspired by visits to the vast 18th-century Jonathan Edwards archives at the Beinecke and accompanied by six black-and-white photograms by James Welling — presents hauntingly lovely, oblique text-collages that Howe (with scissors and "invisible" Scotch Tape and a Canon copier) has twisted, flattened, and snipped into "inscapes of force." The final section, "That This," delivers beautiful short squares of verse that might look at home in a hymnal, although their orderly appearance...