"_It is total reflection!_" That left me cold, but it didn't Bill. I could see that he had a glimmering of an understanding of what went on, but he was puzzled as to the why, what and how. "How d'you mean?" he asked. "We have total internal reflection in prisms. That's no weapon--or defense either, unless you're figuring on Nebel's crowd developing a death-ray or something like that for the next war." Dampier chuckled. It was about as self-satisfied a chuckle as I've heard. "Death-rays--maybe. I do not care. Bullets, shells, bombs, I tell you nothing, _nothing_ can break through the barrier of total reflection! And it is a weapon as well, to turn the enemy's own strength against him." Bill was sitting up straight in his chair. "Tell me about it," he said softly. Dampier wriggled and seemed to settle down like a statue on his two spread legs. Only from the waist up was he alive, talking volubly with both hands and that wagging beard. "It is simple," he explained. "From the beginning of time, what has been the first defense of mankind? It is the wall, the barrier which the enemy cannot climb, cannot break, cannot penetrate with their weapons. A wall of thorns against the beasts of the darkness. A boulder rolled in the mouth of a cave. Walls of sharpened stakes, of earth and stone, of human flesh and blood! Walls of fire laid down by giant guns. Walls of poisonous vapors through which no living thing can pass. Always a wall, stronger and stronger, but never perfect. I, Pierre Dampier, have made the perfect wall! "Look, Monsieur--you have spoken of the reflecting prism. All light that falls on it at the proper angle is diverted, turned back. Walls of steel and concrete, such as I have here about me, will repel the bullets of powerful rifles, the shells of small guns, like the little balls of ping-pong. All these things will protect me from the weapons of my enemies--but they are not perfect. They are not total reflection! "Look you, again. Always there is some ray that will be of the improper angle, the too great or too small wavelength. Always there is some shell that will batter its way through my walls and kill me. But if I can find a mirror that will turn back all rays, a wall from which all projectiles will rebound, a shield against all the many forces of Nature and of man--then, Monsieur, I have the perfect defense and the perfect weapon! "See this little mirror in my hand. I flash in your eyes a beam of light--so. You are blinded, no? And if this is not light, but a ray of death that you have hurled against my mirror, it kills _you_--is it not so? If it is a bullet that you shoot at me, it recoils and strikes you down. If it is a bomb, it is thrown back into your trenches, to kill your men. If it is a great force of pressure or attraction, it is diverted, reversed, and it strikes at you while I am safe behind my perfect wall."