"After adequate doses of your space vitamin, Dad, a skin diver could tackle almost any undersea job in my hydrolung!" Tom exclaimed. "He wouldn't be subjected to any antiosmosis troubles with his body tissues."  
His father nodded. "For the first time, man might become a truly marine creature!"
 
"Wow! Think of it!" Bud gasped excitedly. "With Tom's hydrolung and a knife to hunt his own food, he could practically live in the sea!"
 
"That's no farfetched dream, Bud." Tom's steel-blue eyes flashed at the thought of new fields of scientific conquest. "This discovery of Dad's and Doc Simpson's opens up some really amazing possibilities."
 
Most important at the moment, the vitamin would be a great boon in carrying out search and digging operations for the Jupiter prober. With fresh enthusiasm, Tom returned to his laboratory to work on the new sonar gear. In his own mind, he had already named it a "quality analyzer sonar," since that exactly described the way it would function.
 
"Hmm, let's see," Tom mused as he settled down at his workbench, pencil in hand. "Besides a regular sonarscope, I'll need at least three units for the gear."
 
First, he would 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 Tom brought his eyes into focus, he realized he was back at his workbench in the laboratory. Chow was standing in front of him, holding a half-empty pail of water, ready to splash him again!
 
"Hey! Cut it out!" Tom cried out, jerking bolt upright. Then, as he saw the disturbed look on Chow's face, Tom burst out laughing. "Okay. Relax, old-timer! Guess I was dreaming."
 
"Brand my snake oil!" Chow said. "You looked so pale an' pasty, you had me plumb scared, Tom! I couldn't wake you nohow!" Worriedly the cook added, "What you need is a good beefsteak and some sunshine. You been under water too long."
 
"In more ways than one!" Tom chuckled as he grabbed a towel and dried himself off.
 
The beefsteak, with crisp golden-brown French fried potatoes, was already at hand on Chow's lunch cart. Tom ate with a hearty appetite and the stout............