“So the major gave his guest a hand mirror, and told him to walk around with it until he could see his own teeth, when he would thus know that he was in the path of the beam. But Sir Oliver skirted the laboratory in vain. His teeth never showed up white at all; for you see, he had a set of false teeth, and only _real_ teeth will glow in the black light. Major Wood and I were horribly embarrassed.” “That is all very well,” Lilla broke in, laughing, “but if our men have the black light, and the Formians can’t see it, how can our men see it either?” “A fair question,” her husband replied, “and the explanation is easy. These binoculars, like those used by the American navy in the World War, are equipped with a fluorescent screen, or light filter, the effect of which is to make the black light appear as though it were the ordinary white light to which our eyes are accustomed. Thus to us the light is white, whereas to our enemies it is—well, for them it does not exist at all.” “So that is why the ant men do not dodge, not knowing that they are illumined by the Cupian searchlights, and thus they fall an easy prey to the rifles of the Cupians.” By this time the tide of battle had swept to the southward. The party on the terrace withdrew for much needed rest and refreshment. Cabot was elated, but Nan-nan threw a wet blanket over his hopes. * * * * * “Do not forget,” the young priest reminded him, “that with daylight the Formians will return in full force. What will your black light then avail you?” They separated for the night, Cabot pondering deeply on the parting words of the priest. * * * * * Lilla and Myles made their way to her old quarters, where he had courted her in the days when he had been a mere barsarkar, newly arrived in Kuana, after his escape from the Formians. Here, too, they had lived as guests of King Kew, her father, after their marriage; except of course, during such time as they had spent at their own country residence on the beautiful little island in the midst of Lake Luno. The fatal Lake Luno! In Lilla’s recent captivity under Yuri, she had been permitted to occupy these same quarters. And Bthuh, her best friend, and wife of Poblath, had accompanied her as lady in waiting, and had taken charge as of old. Yuri, still hoping to win the princess, had not violated the sanctuary of those rooms. Lilla and Myles entered the quarters together. “Lie down for a minute on this couch,” she said, “while I find your things.” He obeyed. In a moment she was back, but the weary earthman was sound asleep where he had dropped. Tenderly she kissed the unshaven face; then spread a blanket over him and left him there in the outer room, while she retired to her chamber for the night. The next thing he knew some one was shaking his shoulder. He awoke with a start.