"The temperature under the surface of the earth," said Prof. Shapley, "increases one degree Fahrenheit at every seventy-six feet, about seventy degrees per mile. In some places in California we get the temperature of boiling water at a depth of less than a mile. The center of the earth is roughly 4,000 miles below the surface. "Because of this intense internal heat of the earth it would probably be impossible to maintain permanent laboratories at greater depths than two miles," said the lecturer, "and, in addition, the installation and maintenance of Plutonic laboratories will be a scientific adventure of great difficulty and expense. Yet, if carried on in connection with the work of existing mines and borings it may mark the coming decade as one of the important epochs in man's attempt to understand the earth. "These Plutonic laboratories, placed at various depths under the surface, fully equipped with modern scientific apparatus, and maintained indefinitely, will contribute to our knowledge in a dozen important fields of geophysic and astronomy." What Prof. Shapley pointed to as merely a possible by-product of the proposed scientific "descent into Hades" is the commercial possibility of tapping the earth's internal source of heat. There is 31,000,000 times as much natural heat in the earth than in all the coal resources of the world. He stated that Sir Charles Parsons and John L. Hodgson, both noted British engineers, are already engaged in work on this problem. When Caverns Yawned _By Captain S. P. Meek_ [Illustration: From the bump on the side of the submarine came a flash of red light.] [Sidenote: Only Dr. Bird's super-scientific sleuthing stands in the way of Ivan Saranoff's latest attempt at wholesale destruction.] Bells jangled discordantly. A whistle split the air with a piercing note. A band blared away on the platform. With a growing rumble of sound, the Presidential special slowly gathered headway. The President waved a final farewell to the crowds at the platform and sat down. He chatted cheerily with his companions until the train was clear of Charleston, then rose, and with a word to the others stepped into the car. Operative Carnes of the United States Service slumped back in his chair with a sigh of relief. "Thank Goodness, that's over," he said. "I was never so glad to get him safely away from a place in my life." Haggerty of the secret service nodded in agreement. Colonel Holmes, the military aide, looked up inquiringly. "Why so? Do you think Charleston an especially dangerous place for him to be?" "Not ordinarily. Charleston is a very patriotic and loyal city, but I have been worried. There have been vague rumors going around. Nothing definite that we could pin down, but enough to make me pretty uneasy." "I think you've worried needlessly. I have been in constant touch with the Military Intelligence Division and they have reported nothing alarming."