A diagram, it seemed, but-a diagram of white lines on dark paper! Again he felt the thrill of discovery. It was clearly a blueprint!- and there was not a single original blueprint left at the abbey, but only inked facsimiles of several such prints. The originals had faded long ago from overexposure to light. Never before had Francis seen an original, although he had seen enough handpainted reproductions to recognize it as a blueprint, which, while stained and faded, remained legible after so many centuries because of the total darkness and low humidity in the shelter. He turned the document over-and felt brief fury. What idiot had desecrated the priceless paper? Someone had sketched absentminded geometrical figures and childish cartoon faces all over the back. What thoughtless vandal-