"And you are an American?" asked Tarzan, smiling. "We are not all money mad," replied Gridley. "Then what is the incentive? Explain the whole proposition to me." "Have you ever heard of the theory that the earth is a hollow sphere, containing a habitable world within its interior?" "The theory that has been definitely refuted by scientific investigation," replied the ape-man. "But has it been refuted satisfactorily?" asked Gridley. "To the satisfaction of the scientists," replied Tarzan. "And to my satisfaction, too," replied the American, "until I recently received a message direct from the inner world." "You surprise me," said the ape-man. "And I, too, was surprised, but the fact remains that I have been in radio communication with Abner Perry in the inner world of Pellucidar and I have brought a copy of that message with me and also an affidavit of its authenticity from a man with whose name you are familiar and who was with me when I received the message; in fact, he was listening in at the same time with me. Here they are." From a portfolio he took a letter which he handed to Tarzan and a bulky manuscript bound in board covers. "I shall not take the time to read you all of the story of Tanar of Pellucidar," said Gridley, "because there is a great deal in it that is not essential to the exposition of my plan." "As you will," said Tarzan. "I am listening." For half an hour Jason Gridley read excerpts from the manuscript before him. "This," he said, when he had completed the reading, "is what convinced me of the existence of Pellucidar, and it is the unfortunate situation of David Innes that impelled me to come to you with the proposal that we undertake an expedition whose first purpose shall be to rescue him from the dungeon of the Korsars." "And how do you think this may be done?" asked the ape-man. "Are you convinced of the correctness of Innes' theory that there is an entrance to the inner world at each pole?" "I am free to confess that I do not know what to believe," replied the American. "But after I received this message from Perry I commenced to investigate and I discovered that the theory of an inhabitable world at the center of the earth with openings leading into it at the north and south poles is no new one and that there is much evidence to support it. I found a very complete exposition of the theory in a book written about 1830 and in another work of more recent time. Therein I found what seemed to be a reasonable explanation of many well known phenomena that have not been satisfactorily explained by any hypothesis endorsed by science." "What, for example?" asked Tarzan.