that chance. It's about the only chance. If he fails, three days from today—"

"As bad as that?"

"I'm afraid so. But let's not talk about it. One thing I don't know: How was the formula lost?"

"Dad destroyed it. He discovered it accidentally twenty years ago, while working on something else. Never thinking that the fate of worlds might hinge upon it, he destroyed his notes almost as soon as he had made them. He's always been awfully opposed to war, you know, and he saw the terrible possibilities in the weapon if it should fall into the wrong hands."

"That is still true," said a quiet voice from the doorway. Roger Kay recognized Corvo North at once from the many photographs he had seen. He rose and offered his hand.

"I'm glad you're here, Mr. Kay," said the scientist. "Ann told me you were coming. Yes, it's still true that I'm opposed to war—but this isn't war. Even disregarding personal interests and patriotism, it's an attempt to save the human race. Come on into the laboratory. We've no time to waste."

Roger whistled softly under his breath as Corvo North closed the door behind them. The laboratory, spacious and well equipped, was a research worker's dream.

The scientist led the way past rows of pieces of apparatus whose purpose Roger could but dimly guess, to a table at the far end of the room. Upon the table was a small box bristling with dials. The back and top were open, showing a maze of wires and coils and condensers.

"Looks like a radio set with hydrophobia," Roger observed. "What connection has this with the catalyst formula?"

"Nothing, directly. There's no chance, through experimentation, of my recovering that formula in time. Three years, possibly. Three days, never."

"You mean that it's hopeless to try? That the System is lost?" Roger Kay was appalled.

"I don't quite mean that," said North. "But what chance there is lies through this apparatus you're looking at now. Sit down; I'll explain while I work. You can help later, when I've explained the machine."

He began to tinker amidst the maze of wires.

"My discovery of trionite was purely accidental. It was empiric; not based on any theory. There were six or seven chemicals, and I recall the identity of only two of them. The others? Well, count the chemicals in the 

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