Entry hall 415 was a vast, echo-haunted hall whose high, groin-vaulted ceiling was crossed by a fine, detailed web of cast-iron steam pipes and hollow bronze sounding chimney pipes.
The air here was freezing, and the floor flags were covered in a thin, crackling crust of dried salt-foam that had dried during the last spring surge. Every footstep produced a dry, crystal-clear crunch that rang through the empty aisles like the breaking of thin ice upon a winter pond.
Qiao Ming stood beneath the central junction where eight major air-flow chimney pipes came together into a single upright intake shaft twenty arm-lengths wide.
Before striking the tube, Qiao Ming had carefully measured the air currents rising through the central shaft. He had held a pinch of dry willow-charcoal dust above the lip of the opening, watching how the black specks drifted upward in a tight, helical vortex.
“The draft speed is eight arm-lengths per breath,” he had explained to Yan Zhiqiu. “The incoming tide is compressing the air in the lower ballast chambers, forcing sixty thousand cubic paces of high-pressure wind upward through this chimney pipe. When the tube sings, the sound will not remain nearby in this room. The rising column of air will carry the sound wave straight up into the outer fissures where the swarm is gathering.”
