"The moment a single pie is disturbed," he said to me, "I shall close the steel door from the inside, and you and Miss Barrison will then dump the rosium oxide and the strontium into the tank, clap on the lid, turn the nozzle of the hose on the cage, and spray it thoroughly. Whatever is invisible in the cage will become visible and of a faint rose color. And when the trapped creature becomes visible, hold yourselves ready to aid me as long as I am able to give you orders. After that either all will go well or all will go otherwise, and you must run for the launch." He seated himself in the cage near the open door. I placed the steel tank near the cage, uncoiled the hose attachment, unscrewed the top, and dumped in the salts of strontium. Miss Barrison unwrapped the bottle of rosium oxide and loosened the cork. We examined this pearl-and-pink powder and shook it up so that it might run out quickly. Then Miss Barrison sat down, and presently became absorbed in a stenographic report of the proceedings up to date. When Miss Barrison finished her report she handed me the bundle of papers. I stowed them away in my wallet, and we sat down together beside the tank. Inside the cage Professor Farrago was seated, his spectacled eyes fixed on the row of pies. For a while, although realizing perfectly that our quarry was transparent and invisible, we unconsciously strained our eyes in quest of something stirring in the forest. "I should think," said I, in a low voice, "that the odor of the pies might draw at least one out of the odd dozen that came rubbing up against my window last night." "Hush! Listen!" she breathed. But we heard nothing save the snoring of the overfed dog at our feet. "He'll give us ample notice by butting into Miss Barrison's skirts," I observed. "No need of our watching, professor." The professor nodded. Presently he removed his spectacles and lay back against the bars, closing his eyes. At first the forest silence seemed cheerful there in the flecked sunlight. The spotted wood-gnats gyrated merrily, chased by dragon-flies; the shy wood-birds hopped from branch to twig, peering at us in friendly inquiry; a lithe, gray squirrel, plumy tail undulating, rambled serenely around the cage, sniffing at the pastry within. Suddenly, without apparent reason, the squirrel sprang to a tree-trunk, hung a moment on the bark, quivering all over, then dashed away into the jungle. "Why did he act like that?" whispered Miss Barrison. And, after a moment: "How still it is! Where have the birds gone?" In the ominous silence the dog began to whimper in his sleep and his hind legs kicked convulsively. "He's dreaming--" I began. The words were almost driven down my throat by the dog, who, without a yelp of warning, hurled himself at Miss Barrison and alighted on my chest, fore paws around my neck. I cast him scornfully from me, but he scrambled back, digging like a mole to get under us.