A deep hooing noise, like the resonant tone of an organ pipe. Then the rustle of feathers as the bird squeezed through the opening, and the rhythm of powerful wings, like the beating of a heart, receding into the sky. The spectrum of Venus flashed off, then on, as the owl momentarily eclipsed the planet. When Daniel looked, he realized that he could now see not only the spectrum from Venus, but tiny, ghostly streaks of color all over the wall: the spectra cast by the stars that surrounded Venus in the southern sky. But spectra were all he could see. The earth spun and the ribbons of color migrated across the invisible wall, an inch a minute, pouring across the rough plaster like shining puddles of quicksilver driven before a steady wind, revealing, in gorgeous colors, tiny strips of the pictures that Isaac had drawn and scratched on those walls. Each of the little rainbows showed only a fragment of a picture, and each picture in turn was only part of Isaac's tapestry of sketchings and scratchings, but Daniel supposed that if he stood there through a sufficient number of long cold nights and concentrated very hard, he might be able to assemble, in his mind, a rough conception of the entire thing. Which was the way he had to address Isaac Newton in any case.