He knew they gave off both visible and invisible rays.

An invisible ray fired the dry brush between him and the dog.

Not only there, perhaps, but in the other two Cities as well; for the messages would go to them immediately on the invisible rays.

There would be alarms too, invisible rays which set off a warning the moment you walked into them.

Derek pushed buttons, and the invisible rays from the screen show a new picture.

He explained that the action of the invisible ray was entirely harmless to human tissue.

A different kind of invisible ray, the scientists think, which kills all electrical things when it is used.

The invisible black ray, focused on the heavy steel plate, made the laboratory seem suddenly chilly.

In the active method an invisible infra-red ray is emitted.

Its invisible black ray would never melt battleship steel at six inches or any other distance.