“Even in the case of a rolling ship,” Kennedy continued, alternately covering and uncovering the mirror, “the beam of light which this mirror reflects always goes back, unerring, to its source. It would do so from an aeroplane, so high in the air that it could not be located. The returning beam is invisible to anyone not immediately in the path of the ray, and the ray always goes to the observer. It is simply a matter of pure mathematics practically applied. The angle of incidence equals the angle of reflection. There is not a variation of a foot in two miles.”
“What message are you sending him?” asked Verplanck.
“To tell Mrs. Hollingsworth to hurry home immediately,” Kennedy replied, still flashing the letters according to his code.
“Mrs. Hollingsworth?” repeated Verplanck, looking up.
“Yes. This hydroaeroplane yeggman is after something besides jewels to-night. Were those letters that were stolen from you the only ones you had in the safe?”
Verplanck looked up quickly. “Yes, yes. Of course.”
“You had none from a woman—”
“No,” he almost shouted. Of a sudden it seemed to dawn on him what Kennedy was driving at—the robbery of his own house with no loss except of a packet of letters on business, followed by the attempt on Mrs. Hollingsworth. “Do you think I’d keep dynamite, even in the safe?”
To hide his confusion he had turned and was bending again over the engine.
“How is it?” asked Kennedy, his signaling over.