Dwellers in Darkness: The Golden Amazon Saga, Book Fourteen. John Russell Fearn

Geiger counter instrument in her hand. It was clicking industriously, and continued to do so whichever way she moved it.

      “Mmm, certainly pretty strong,” Abna agreed, looking about him. “Wonder what the cause is?”

      Together they looked around them, but beheld nothing that might account for the phenomenon; then the Amazon said;

      “This instrument is extremely sensitive, don’t forget. It would pick up radioactivity even if it were located on the other side of the planet. The impulses seem to be the strongest in.…” She tested the instrument carefully. “In that direction,” she said finally. “Due north.”

      “Where there’s apparently nothing but flat plain. Only one thing we can do—use the Ultra and travel northwards to investigate. Let’s be going.”