A description of Mercury is provided. Mercury is white hot on the side that always faces the Sun, and covered in giant crystals on its dark side. The tension between the hot and cold, light and dark sides of the planet cause it to vibrate, or "sing".
There are deep caves on Mercury, inhabited by simple, flat creatures called harmoniums. These creatures feed on the vibrations of the planet and cling to the phosphorescent walls of the caves. Harmoniums are like "small and spineless kites" (p. 185) and they reproduce by flaking off pieces that begin to grow. For an unknown reason, the creatures often arrange themselves in regular patterns on the walls, glowing aquamarine where the yellow light from the walls passes through their bodies.
Unk and Boaz's ship approaches the dark.....
