Pensive, mercurial, and often funny, the private Robert Frost remains less appreciated than the public poet. The Letters of Robert Frost, the first major edition of the correspondence of this complex and subtle verbal artist, includes hundreds of unpublished letters whose literary interest is on a par with Dickinson, Lowell, and Beckett. Volume 2. "In the years covered here, publication of Selected Poems, New Hampshire, and West-Running Brook enhanced...