"Both of these were developed by my brother Philip and me together—but we have disagreed about the use to which they shall be put.

"Philip"—the inventor dropped his voice to a whisper—"wants to sell the secret of the Death Projector—the tower, there—as an instrument of war. If I should permit him to do that, it might lead to the destruction of whole nations!"

"How?" demanded Quest "I've heard of a device called the Death Ray. Is this it?"

"No, no," said Clason contemptuously. "Even in a perfected state the Ray would be a child's toy compared to the Projector. This is based on our discovery that invisible light rays of a certain wave-length, if highly concentrated, destroy life—and our additional discovery that if these are synchronized with short radio waves the effect is absolutely devastating.

"We obtain the desired concentration of invisible light by using a tellurium current-filter under the influence of alternate flashes of red and blue light. The projector can literally blanket vast areas with death, up to a top range of at least five hundred miles.