heat lightning

His face had altered; a dim glimmer played in his eyes like the reflection of heat lightning at dusk.

The night was pitch dark, except for pulses of heat-lightning, now and then, far to westward.

A pale flare of heat-lightning turned the world, momentarily, from jet black to a dim sulphur-color.

In the south, too, "heat lightning" played sharply—and almost continuously.

The sky quivers and reflects the flash of the great guns, as with the constant vibration of heat lightning.