At three hundred and twenty feet, the character of the air underwent a brutal, violent transformation.
Below three hundred feet, the city’s vast maze of slate roofs, brick chimneys, and high church steeples offered a degree of friction that broke the teeth of the river gale. But above the level of Saint Jude’s cross, the air was raw, unhindered, and terrifyingly fast.
The wind didn’t blow in steady, predictable streams. It poured off the northern estuary like a torrent of icy water through a narrow mountain gorge, striking the curved western flank of the Spire and splitting into two violent, screaming vortexes that whipped around the tower’s shoulders at forty-five knots.
This wind-cutting phenomenon—what Master Land-mappers called the vortex shedding street—created alternating zones of high pressure and violent suction on the tower’s leeward flanks. The vortices broke away from the stone at intervals of two to three seconds. Then, they exerted a rhythmic lateral tug that made the entire six-hundred-foot stonework chimney sway like an inverted swinging weight.
Tomas watched a flock of river gulls trying to round the tower sixty paces below. The birds entered the leeward shear zone. Then, the dropping tip vortex slammed them downward sixty upright feet in a heartbeat, their wings tumbling in wild disarray before they broke away toward the harbor. If the air currents could overpower the wings of gulls, the dead load on a suspended human body was huge.
