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!

"Fuse blew," said Barney shortly. He gumbled his way through the dark house and replaced the fuse. He returned smiling. "Fixed that one," he told Jim. "Put a washer behind it."

"O.K. Hit the switch again."

Barney cranked the power over, and once more the meters climbed up across the scales. There was a groaning sound from the tube, and the smell of burning insulation filled the room. One meter blew with an audible sound as the needle hit the end stop, and immediately afterward the lights in the entire block went out.

"Fix that one by hanging a penny behind it," said Jim with a grin.

"That's a job for Martian Electric to do," laughed Barney.

Several blocks from there, an attendant in the substation found the open circuit-breaker and shoved it in with a grim smile. He looked up at the power-demand meter and grunted. High for this district, but not dangerous. Duration, approximately fifteen seconds. Intensity, higher than usual but not high enough to diagnose any failure of the wiring in the district. "Ah, well," he thought, "we can crank up the blow-point on this breaker if it happens again."

He 

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