could not be a refrigeration-apparatus without metal.

He put the induction balance away. He stuck a thermometer into the hole he'd made earlier. He moved it carefully back and forth, watching the mercury shrink. He swallowed when he saw its final reading. He hooked up the thermocouple--infinitely thin wires, of different metals, joined at their tips. He hooked on the microvoltometer. He soon found a particular spot. It was a very particular spot indeed. The tips of the wires had to be at an exact depth inside the hole. A hundredth of an inch off made the microvoltometer sway wildly. He changed a connection to get a grosser reading--millivolts instead of microvolts--and found that exact depth in the hole again. He went pale.

Laurie said: "Tommy, I'm back."

He turned and said blankly, "A hundred and ninety millivolts! And it's below the temperature of dry ice!"

Laurie said wistfully, "I can't even raise the temperature of that, can I, Tommy?"

He didn't notice. He put down the thermocouple and brought out the alnico magnet. He wrestled the keeper off its poles.

"This doesn't make sense," he said absorbedly, "but if it is a field of force...."

He turned again to the wall and the hole he'd made in it. He put the heavy, intensely strong magnet near the opening.

The opening clouded. It acquired a silvery sheen which had the look of metal as the magnet neared it. Coghlan pulled the magnet away. The look of metal vanished. He put the magnet back, and the silvery appearance was there again.

He was staring at it, speechless, when Mannard came over with Ghalil and Duval. Mannard carried the thick, ancient volume with the battered ivory medallions in its cover--and Coghlan's seven-hundred-year-old fingerprints on its first page.

"Tommy," said Mannard uncomfortably, "I don't believe this! But put one of your fingerprints alongside one of these, dammit!"

Ghalil matter-of-factly struck a match and began to make a deposit of soot on the scraping-tool which he'd used to pull down plaster. Coghlan ignored them, staring at the hole in the plaster.

"What's the matter with him?" demanded Mannard.

"Science," said Laurie, 

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