Isaac's bedroom might have been designed specifically for doing prism experiments, because one wanted an opening just big enough to admit a ray of light in which to center the prism, but otherwise the room needed to be dark so that the spectrum could be clearly viewed where it struck the wall. The only drawback for Daniel was stumbling over debris. This was the room where Isaac had lived in the years before going to Cambridge. Daniel inferred that they had been lonely years. The floor was cluttered with stuff Isaac had made but been too busy to throw away, and the white plaster walls were covered with graffiti he had sketched with charcoal or scratched with nails: designs for windmills, depictions of birds, geometrickal proofs. Daniel shuffled through the darkness, never lifting a foot off the floor lest it come down on an old piece of doll-furniture or jagged remains of a lens-grinding experiment, the delicate works of a water-clock or the papery skull of a small animal, or a foamy crucible crowned with frozen drips of metal.