Books: Music of the Spheres

THE SLEEPWALKERS (624 pp.)—Arthur Koestler—Macmillan ($6.50).

Arthur Koestler, 53, is an ex-rebel without a cause. In the '305, he was a Communist; in the '40s and well into the '50s, a trenchant antiCommunist. While he remains as firmly anti-Red as ever, he seems to have wearied of the battle. A few years ago, the author of Darkness at Noon announced: "Cassandra has gone hoarse and is due for a vocational change." Lately, the polemicist has turned pedagogue. The Sleepwalkers is an animated and diverting lecture on cosmology, man's vision of the universe from the...