Absorbed in the discussion of these matters, no one noticed the entrance of Sajipona. The queen, coming from the apartment where she had left David and Raoul, was not in a hurry to make her presence known, and lingered long enough behind the others to enjoy the curiosity and wonder with which they were regarding the globe of light above them. She now advanced smilingly, addressing herself particularly to Leighton, whom she complimented for his shrewd guess as to the nature of the force pervading and governing the cave. Indian though she was, inheritor of a realm that, in all its customs and beliefs, was primitive, distant from the civilizations found elsewhere in the world to-day, she had heard and studied enough of Europe and America to be familiar with some of the momentous discoveries of modern science. Hence, she had been quick to grasp the fact that this subterranean sun, worshiped by her ancestors ages ago as the Life Giver--the God that, according to Indian legend, resided under Lake Guatavita--was nothing more nor less than an immense body of radium, the most precious substance known to man, the scarcity of which had led scientists to ransack the uttermost parts of the earth in the hope of adding to their store of it. Here it had always been, the one priceless possession of her people, enabling them to live apart, independent of the world that threatened at one time to exterminate them. How this radium had come there originally she could not tell. It was the result, doubtless, of hidden forces about which philosopher and scientist are as yet ignorant. Or, it might itself be the architect of the subterranean world whose extent and manifold marvels had amazed the explorers. By means of this radium force, as Una had told them, she was able to see what was happening in any part of the cave, even throughout that dark region lying beyond the Condor Gate--an incredible statement, as it appeared to Leighton. For they had been in this outer cave and discovered in it neither the light nor the warmth they had enjoyed on this side the Condor Gate. Hence, argued the savant, this outer cave appeared to lie entirely beyond the zone of radium influence. Sajipona smiled at Leighton's objection and asked him if nothing had occurred in the outer cave, while he was there, that he had been unable to explain. They had been through so many marvels in so short a time that the explorers looked at each other doubtfully. Mrs. Quayle answered for them. "Yes, the terrible stone that pulled off my jewelry, and then dragged gold up from the lake outside--how was that done?" she asked, still smarting, apparently, from the indignities she had suffered.