by Random House, $19.95. Lowell suffered from a condition that bounced him in and out of mental hospitals through most of his adult life. His story would be intolerably depressing if a biographer confined it to such practical fact, but as a poet himself, Mr. Hamilton has devoted much of his book to examining Lowell’s work and elucidating his methods, which he does superbly. He has also incorporated material from Lowell’s many literary associates, accomplished writers whose styles and points of view provide a variety that counteracts the monotony of Lowell’s illness. A fine biography of a fine poet who was, as one comes respectfully to realize, a brave and resolute man..