"A goofy idea just occurred to me, but I think it may work out," Tom replied. He seized a pencil and began explaining what he had in mind.
The drive unit would take water into itself, separate the ionized molecules, and expose them to an electric field. Thus a stream of water would be forced out. This procedure, in turn, would set up a siphoning action through a central tube—in effect, creating a small but powerful water-jet motor.
"We'll be human submarines!" Bud exclaimed.
By the time Bud left the laboratory half an hour later, Tom had already plunged into work on his newest invention. The idea was simple enough in itself, Tom felt. The main problem would be the design job—laying out a compact, lightweight unit which a swimmer could easily carry on his back.
Fascinated, the young inventor worked late into the evening, stopping only in response to a telephone plea from Mrs. Swift. By midmorning the next day, Tom had assembled a pilot model of his ion-drive jet. In appearance, it was a slender metal cylinder, two feet long, with an inner concentric tube projecting at each end.
Tom had ordered a tank set up in his laboratory to test the unit. The tank was filled chest-deep with water, and the ion drive was mounted on a unitrack running the length of it. Tom set up his control board alongside, with the main power switch within easy reach. The drive unit was connected to the board by a suspended cable.
"Boy, this'll be like playing with a speedboat in a bathtub!" Tom thought with a chuckle as he changed into swim trunks.
He climbed into the tank and slid the drive unit to one end of its track. Then Tom metered out power slowly. With a gentle whoosh, the ion-drive unit whizzed along the unitrack to the other end of the tank.
"Not bad," Tom muttered, a pleased grin on his face. "Now I'll rev it up a little."
He slid the drive unit back to starting position, then opened the switch wider. He had just started across the tank himself when suddenly he became powerless to move.