“For one thing, it shows up in the ground temperature. You see, up in the north polar regions, the soil is covered with a solid layer of permafrost all year round. But down south, in the Antarctic, you find spots that are warm and free from snow.
“Also, magnetic flux lines enter the earth near the South Pole.”
“Those are pretty good arguments,” Mr. Swift conceded. “But your mother is still right. Even at the South Pole, that molten iron must be several hundred miles down. And that would take a lot of digging, even for your atomic earth blaster.”
“It would leave quite a pile of dirt, too, I should think,” put in Sandra with a laugh.
Mr. Swift pulled a small slide rule out of his pocket and did some hasty figuring.
“Suppose you dug a pit three feet in diameter,” he said. “For every hundred miles you went down, you’d haul up enough dirt to cover six square city blocks and piled three times as high as the Empire State Building!”
“Golly!” Sandy gasped, and for the first time expressed some doubts about her brother’s plan.
But Tom had a solution. “We could get around that by changing the design of the earth blaster.”
DANGER SIGNAL 27
“How?” his father asked.
“Instead of using the atomic energy to grind up the dirt and rocks, we could use it to power an electric smelter. This would release gaseous oxygen from the melted rock. And the gas in turn would billow up the shaft, carrying the particles of ore dust with it, so we wouldn’t need a conveyor.”
Mr. Swift tugged at his lower lip and nodded thoughtfully. But Uncle Ned shook his head.