"Yeah," drawled Jim. "About the same recognition as the difference between Edison's first electric light and a twelve-element, electron multiplier, power output tube. Similarity: They both have cathodes." "Edison didn't have a cathode--" "Sure he did. Just because he didn't hang a plate inside of the bottle doesn't stop the filament from being a cathode." Barney snorted. "A monode, hey?" "Precisely. After which come diodes, triodes, tetrodes, pentodes, hexodes, heptodes--" "--and the men in the white coats. How's your patching job?" "Fine. How's your power-supply job?" "Good enough," said Barney. "This eighty-four cycles is not going to be a sine wave at two hundred volts; the power stage of the BFO overloads just enough to bring in a bit of second harmonic." "A beat-frequency-oscillator was never made to run at that level," complained Jim Baler. "At least, not this one. She'll tick on a bit of second, I think." "Are we ready for the great experiment?" "Yup, and I still wish I knew what the thing was for. Go ahead, Barney. Crack the big switch!" * * * * * Altas held up a restraining hand as Than grasped the main power switch. "Wait," he said. "Does one stand in his sky flier and leave the ground at full velocity? Or does one start an internal combustion engine at full speed?" "No," said the youngster. "We usually take it slowly." "And like the others, we must tune our tube. And that we cannot do under full power. Advance your power lever one-tenth step and we'll adjust the deflection anodes." "I'll get the equipment," said Than. "I forgot that part." "Never mind the equipment," smiled Altas. "Observe." Altas picked up a long screw-driverlike tool and inserted it into the maze of wiring that surrounded the tube. Squinting in one end of the big tube, he turned the tool until the cathode surface brightened slightly. He adjusted the instrument until the cathode was at its brightest, and then withdrew the tool. "That will do for your experimental set-up," smiled Altas. "The operation in service is far more critical and requires equipment. As an experiment, conducted singly, the accumulative effect cannot be dangerous, though if the deflection plates are not properly served with their supply voltages, the experiment is a failure. The operation of the tube depends upon the perfection of the deflection-plate voltages." "No equipment is required, then?" "It should have been employed," said Altas modestly. "But in my years as a beam-tower attendant, I have learned the art of aligning the plates by eye. Now, son, we may proceed from there." * * * * * Barney Carroll took a deep breath and let the power switch fall home. Current meters swung across their scales for an instant, and then the lights went out in the house!