ld need an oscillator to produce the complex pulse. Next,
of course, an oscilloscope to check the pulse as it was beamed out.
Last--but highly important--a correlation calculator.

This latter unit would compare the original pulse with the returning
echoes. If an echo had a high enough "standard of acceptance"--that is,
if its quality was very near the original pulse, it would show up on the
screen in the normal way. If the echo came back blurred, or if "shadow
echoes" showed up, these would be separated and appear on the screen
colored red.

"Whew!" Tom sighed as he realized the complicated job of circuit design
that lay ahead. "This sure is going to burn some midnight oil!"

The young inventor worked all afternoon at a furious pace, breaking off
toward dinnertime to telephone his mother that he would be staying
overnight at the lab. After a hasty meal, he resumed his layout job at
the drawing board and by midnight had finished designing his quality
analyzer sonar.

Whipping off his eyeshade, Tom went into the apartment next door and
stretched out to snatch a few hours' sleep. But as usual when in the
midst of an exciting new project, he was too keyed up to rest for long.

Before daylight, Tom was back at his workbench ready to begin assembling
the units of his new sonar gear. Later he phoned Chow but scarcely
paused to eat when the cook arrived with his order.

"Brand my solar stovepipe!" Chow scolded. "Take time to eat your vittles
properly, boss!"

"Hmm?... Oh, sure." Tom looked up and grinned.

The stout old Texan stomped out, shaking his head.

As the morning wore on, the pace at which Tom had been working began to
tell on the young inventor. His head nodded again and again. Gradually
he fell forward into an exhausted doze.

The next thing Tom knew, he was sailing through the air, high above
Swift Enterprises. Lake Carlopa was a tiny blue puddle below, and the
town of Shopton a mere cluster of toy buildings in the distance.

"Good grief!" Tom exclaimed with a gulp. "What's keeping me up?"

He was floating freely, without the support of any aircraft--or even one
of his amazing force-ray repelatrons!

The discovery triggered off disaster. Like a character in a movie
cartoon, now that he knew he had nothing to support him, Tom instantly
went plunging downward--down, down, straight into the lake!

_Splash!_

Tom gasped and shuddered and shook his head like a drenched terrier.

_Another splash!_ As T