Heath said, "Are you afraid, breaking the tabu?" "Habit is hard to break." She turned to him and asked, "What is the Moonfire?" "Haven't the priests told you?" "They say that Venus once had a moon. It rode in the clouds like a disc of fire and the god who dwelt within it was supreme over all the other gods. He watched the surface of the planet and all that was done upon it. But the lesser gods were jealous, and one day they were able to destroy the palace of the Moon-god. "All the sky of Venus was lighted by that destruction. Mountains fell and seas poured out of their beds and whole nations died. The Moon-god was slain and his shining body fell like a meteor through the clouds. "But a god cannot really die. He only sleeps and waits. The golden mist is the cloud of his breathing, and the shining of his body is the Moonfire. A man may gain divinity from the heart of the sleeping god but all the gods of Venus will curse him if he tries because man has no right to steal their powers." "And you don't believe that story," said Heath. Alor shrugged. "You have seen the Moonfire. The priests have not." "I didn't get to the heart of it," Heath said. "I only saw the edge of the crater and the light that comes up out of it, the lovely hellish light." He stopped, shuddering, and brooded as he had so many times before on the truth behind the mystery of the Moonfire. Presently he said slowly, "There was a moon, of course, or there could be no conception of one in folklore. I believe it was radioactive, some element that hasn't been found yet or doesn't exist at all on Earth or Mars." "I don't understand," said Alor. "What is 'radioactive'?" She used the Terran word, as Heath had, because there was no term for it in Venusian. "It's a strange sort of fire that burns in certain elements. It eats them away, feeding on its own atoms, and the radiation from this fire is very powerful." He was silent for a moment, his eyes half closed. "Can't you feel it?" he asked. "The first little fire that burns in your own blood?" "Yes," Alor whispered. "I feel it." And Broca said, "It is like wine." Heath went