"I apparently have," was the grave admission. "But do not let it seem such a miracle. Bear in mind, as I have pointed out before, that nature has accomplished this alchemy many times. All radio-active elements are evidences of it. The feat consists merely in altering the valence of the atom, changing its electric charge, in other words. What I have done in the present instance is merely to speed up a process nature already had under way, inasmuch as we are dealing with a radio-active substance." "But what has happened to the by-product of the reaction?" "Your guess is as good as mine. I have not had time to study that phase of it. Heat, mainly, was produced. Possibly a few atoms of helium. But the substance is gone. That is our chief concern just now." It was only after abandoning chemical means and turning to physics that he had met with success, he said. Cathode rays had finally proved the key to the riddle. "But do you think this thing will work on a big scale?" asked Jim regarding that fragile tube doubtfully. Professor Wentworth hesitated before replying. "I do not know," he admitted, "but I intend to find out--to-night." * * * * * Jim looked at him in amazement. "To-night?" "Yes. Or rather, the experiment will be at dawn. If successful, this continent at least will be rid of the menace." Jim's amazement turned to incredulity and a sudden fear gripped him. Had the strain of the past few weeks unbalanced the professor's mind? "But surely you can't hope to wipe them out with one tube. Why, it would take hundreds." "No, only one. You see, I am going to place the tube in the center of the circle and direct its rays outward toward the circumference in a swinging radius." Whereupon, for a moment, Jim's fear seemed confirmed. "But, good God!" he exclaimed. "It couldn't possibly be that powerful, could it?" "I think it can be made to be," was Professor Wentworth's grave assurance. "The greatest power we know in the universe is radiant energy, which reaches us from the sun and the stars, traveling at the speed of light." "Like light rays, these heat rays can be focused, directed; and the beta rays of the cathode, traveling at the same velocity, can be made to ride these rays of radiant heat much as electric power rides radio waves. The giant, in short, can be made, to carry the dwarf, with his deadly little weapon. That, at least, is the theory I am acting on." This somewhat allayed Jim's fears--fears that vanished when the professor went on to explain somewhat the working of his mechanism. "But how are you going to get the thing out there?" he asked, picturing with a shudder the center of the flaming hell. "I imagine the War Department will provide me with a volunteer plane and pilot for the purpose," was the calm reply. "And you will go?" "Yes, I will go." Jim debated, but not for long.