Horace Walpole was a significant figure in literary history, but his reputation would stand even higher if he had excelled in what today are regarded as the "major" genres. He wrote a pioneering book which initiated the Gothic novel; he produced a high-flown tragedy which impressed the Romantics; and he composed serviceable verse satires, a favorite Augustan form. Yet none of these works represents his main achievement. It is in a category now relegated to "miscellaneous prose" that Walpole made an imperishable contribution to literature: first, in a remarkable series of historical memoirs, bequeathed to posterity at his death, and second, in some four thousand personal letters, which many consider the finest body of private correspondence in the English language. In addition Walpole, a leading virtuoso of his day, compiled the engaging Anecdotes of Painting in England (1762-1780); catalogued the productions of "Royal and Noble Authors"; and ruffled...