“The black light?” Lilla inquired. “What is that? How can light be black?”
“They are using the black light,” Myles continued, “just as my country, America, did to protect our convoys in the last great war on my own planet, Minos. Our warships swept the waters far and near with beams of the black light. These beams could not be seen by the German submarines, and thus did not reveal the position of our ships. When a beam played full upon a submarine, the luckless craft even then did not realize that it was observed; did not realize its fate until the high explosive projectile followed close in the wake of the light. Thus the scourge was driven from the seas, and the Germans never even suspected how it was done. I have discussed it with Toron, so this must be his idea.
“Your glowing teeth and eyes revealed the secret to me, O Nan-nan. And that reminds me of a funny story. Major Rob Wood, of the American army, the inventor of the black light, was once demonstrating it in his laboratory to Sir Oliver Lodge shortly after the close of the war. The room appeared to be in darkness, and yet in fact a powerful searchlight was throwing a beam of black light straight across the middle of the room.
“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?”