"He always seemed more alive than other people," Elizabeth Bishop once said of Randall Jarrell, "as if constantly tuned up to the concert pitch that most people, including poets, can maintain only for short and fortunate stretches." And in no area of his diverse writing career was Jarrell more full of life--more "tuned up"--than in his brilliant essays. As a critic, Jarrell was chiefly interested in poetry, but his wide and avid circle of readers...