Cinema: Can Dance a Little

They were all dancers. Cagney propelled himself through space like a bullet or a bull terrier, his torso a few seconds ahead of his legs; anyone without a dancer's equilibrium would have fallen on his face. Fonda was just the opposite: a triumph of convex geometry, his thin body a question mark that ambled at Stepin Fetchit pace toward a girl or a cause.

Hepburn seemed always on the ascendant, scaling the invisible ramp of her own confidence. But it was Fred Astaire who defined screen movement, for the '30s and forever. With athletic...