Minutes ticked away. More than sixty of them were gone before the books were in his hands at last. Did they hold any plans? Diagrams never seen before by Research? The titles-- Carefully he deciphered them from the crushed covers. "A History of the World: 1800-1962." "The P-s-y-c-h-o-l-o-g-y of H-u-m-a-n Relations." "The P-h-i-l-o-s-o-p-h-i-e-s of P-l-a-t-o, S-o-c-r-a-t-e-s, and A-r-i-s-t-o-t-l-e." The fourth title he did not understand at all because he could not read it. He knew only one of its three words, and it made even less sense than the other titles. Quickly, he flipped through the volume for a possible hint of explanation, and there were-- Diagrams!-- Hundreds of them, and one especially beautiful one, larger than the rest--it was necessary to unfold it from the book--in color! It was obviously the only important one of the four books; the others, from what he could gather from their rather vague titles, had nothing to do with building anything--but this one, with diagrams, obviously did! In a haste accompanied with what he knew to be too little caution, Markten's young aide hastened back the way he had come, sometimes stumbling in his anxiety to present his invaluable find to the Elder, once almost falling. But it took only minutes until he found Markten, who was still examining the ruin on its ground level, near the large opening through which they had entered. "Markten! Look--" There was an ominous rumbling sound, then a terrifying feeling of the vibration of disintegration. * * * * * They bolted for the opening even as the still-standing masonry which formed it began to topple. The rumbling increased to thunder-volume, and the earth outside the collapsing ruin quaked beneath their running feet. When they finally stopped at a safe distance, their night-lamps showed only a slowly rising cloud of pumice and dust. "How often," Markten said, when it at last was over, "do you forget the fundamentals of your basic training?" "I--" "It's done now. But the contents of whatever lower levels there may have been are lost to us for good. Nothing could have survived that. And we have never built a digging machine. There probably was nothing, anyway, but next time--" Then Markten saw the book in his aide's hand. The look of disappointment on his features changed suddenly to one of disbelief, then to amazement. "At least I saved this! It has diagrams, Markten! The cave-in I caused destroyed three other books, but they had no drawings in them at all. Here. See if you can understand the title." "Let's get to the laboratory compartment of the plane, where we can see something! Great electrons, boy, what made you hold this back?" Under the powerful lamps in the lab compartment of their aircraft, Markten and the finder of the book puzzled over the three words on its cover and fly-leaf. "Perhaps, in one of the dictionaries at Research headquarters--"