The timber water chute of the canal race shuddered under eighty tons of plunging water.
Spanning the twenty-foot stonework water gate, a huge undershot waterwheel turned with majestic, irresistible torque. Its twenty-four curved oak paddles, banded in rolled wrought-iron plates, sliced through the foaming torrent at twelve turns a minute.
The six-inch square iron axle, forged by Borin Bronze-Lung and seated in bronze pillow-block bearings lubricated with beef animal fat, didn’t squeak. It hummed.
“Torque output is about thirty-six hundred foot-pounds,” Giles Croft said, resting his hand against the timber framing of the blower shed.
“Spinning speed is low. But the angular driving force of the twelve-foot wheel provides excellent damping against cyclical piston pushback.”
Master Caleb Thorne-Wood stood on the narrow high walkway above the crank gearwork. He held an iron oiler can.
Connected to each end of the main axle was a quirky cast-iron crank-arm with an eighteen-inch throw. He drove two massive timber connecting rods framed in seasoned white ash.
The rods reached into the open ends of two huge wooden cylinders, each eight feet long and twenty-four inches in width, turned from hollowed red cedar baulks.
The cedar cylinders had not been easy to bore.
Three weeks earlier, Master Caleb Thorne-Wood had mounted two massive eight-foot logs of straight-grained red cedar onto a water-powered boring lathe set up beside the saw-pit.
A cruciform cutter head tipped with Borin’s case-hardened steel blades had crept through the heartwood, inch by painful inch. It scraped out shavings that smelled of sweet resin and forest soil until the inner bore was true to twenty-four inches from pipe rim to pipe rim.
“Cedar doesn’t rot in damp air,” Caleb said, wiping grease from his calloused palms. “And it doesn’t shrink across the grain like birch or ash.
But wood has pores. If you don’t seal the grain, high-pressure air will bleed through the walls like water through a sieve.”
Giles had solved that problem with three coats of hot beeswax mixed with boiled linseed oil, applied under pressure until the wood drank the sealant deep into its blood-vessel canals.
The inside of each metal tube was as slick and smooth as a polished gun barrel.
Inside the bore slid the piston heads, built of alternating layered maple discs glued with waterproof casein glue.
The edge of each piston was grooved to receive three wide rings of thick, vegetable-tanned harness leather, cupped outward toward the pressure face.
“When the piston drives forward,” Giles explained to Toby, “the air pressure forces the flexible leather lip tight against the cedar wall. The higher the pressure, the tighter the seal.
Self-energizing clockwork packing. It was standard practice for town waterworks pumps for three hundred years.”
“Double-acting,” Caleb shouted down over the churning roar of the spillway. “Pistons push air on the forward stroke and pull air on the back-stroke! Four leather flapper boxes on each metal tube.”
Inside each cedar metal tube slid an eighteen-inch thick piston head built of layered maple discs. It was wrapped around the outer rim with three layers of heavy, animal fat-soaked harness leather.
The leather cup seals flared outward against the metal tube walls under air pressure. That created an airtight sliding seal that hissed like an irritated snake on every stroke.
CHUG-HISS. CHUG-HISS.
The sound was deep, rhythmic, and hypnotic.
Every five seconds, the left piston completed its forward thrust. That forced fifteen cubic feet of tightly packed air through an iron pipe hub into the main blast pipe.
The left piston reached its stroke limit. Then, the right piston surged forward, picking up the volume shifted weight without a split second of lag.
Borin Bronze-Lung stood beside the copper pipe hub. He held his hand near the main discharge valve. A gale of cold, high-pressure air roared against his calloused palm, blowing his copper-braided beard flat against his collar.
“By the seven bellows of Karak-Thurn,” Borin shouted, laughing so hard that tears welled in his red eyes. “It doesn’t stop!
It doesn’t pant! It doesn’t drop the handle to wipe sweat from its forehead.”
Thorgan Ironvein, who had ridden down from the Under-Pass with a heavy cart of graphite crucibles, stood beside Borin with his mouth open.
He reached up, touching the trembling wood of the cedar metal tube with two trembling fingers.
“A wooden chest that breathes,” Thorgan whispered in dazed respect. “The river turns a wheel, and the wheel pumps the breath of forty blacksmiths into an iron pipe.
How... How does the wind know when to enter and when to strike?”
“Aimed gravity flap valves,” Giles explained, adjusting his glasses. “Animal fat-treated leather flaps backed with sheet brass. When the piston retracts, internal metal tube pressure drops below surrounding, allowing air pressure to push the intake flaps open.
When the piston advances, internal squeezing slams the intake flaps shut and forces the discharge flappers open into the pipe hub. No intelligence needed. Standard differential pressure mechanics.”
Thorgan looked at Giles, his slate-grey eyes wide with solemn confusion.
“You build an engine out of cedar trees and leather boots,” Thorgan murmured, “and it sings the song of the mountain drakes.
Our high clan smiths would have spent three ages forging bronze bellows to achieve half this draft.”
“They would have wasted three ages of capital waste,” Giles noted dryly.
“Wood is lighter, cheaper, and self-damping under shaking. If a cedar stave warps, Caleb can replace it in an afternoon with a drawknife.”
Lady Millicent Croft walked along the wooden boardwalk of the mill terrace. Her thick parchment tally-book was held firmly against the river breeze.
“Every stroke of those pistons consumes two drams of beef animal fat from the grease cups,” Millicent noted. He tapped her pencil against the page.
“That’s twelve pounds of refined animal fat every twenty-four hours to keep the leather soft. The kitchen butcher can’t supply that much fat from sheep heads alone, Giles.”
“Mistress Pippa has already rendered thirty gallons of fish oil from the lake carp netted in the lower drainage canal,” Giles replied.
“When blended with twenty percent beeswax, it forms an ideal heavy lubricant with high film strength. We’ll not need to touch the animal fat reserves.”
Millicent made a neat checkmark in her margin. “Acceptable. Provided the foundry doesn’t smell of fried cod during ducal inspections.”
Beside her, Toby Karr was kneeling by the main pipe hub gauge. He watched a small column of red liquid resting in an upright glass U-tube.
“Water column shows one hundred and five inches, Lord Giles,” Toby called out, squinting at the scale. “That converts to exactly three point eight pounds of pressure of static blast head.”
“A very respectable pressure,” Giles said, inspecting the spirit level on the copper discharge collar. “High enough to penetrate the thirty-foot burden column without causing too much fluidization of the peat coke bed.”
Sister Teresa of the Pure Cistern walked along the blower pipe hub. She carried a small clay jar of carbolic vinegar and a clean linen cloth.
She wiped down the brass hinge pins of the leather flapper valves. She nodded in deep sanitary satisfaction.
“No soot in this wind,” Teresa proclaimed. She held her cloth up to the roaring air jet.
“Pure river air, washed clean by the spray of the spillway. The fire will breathe the breath of life, uncontaminated by the lung-rot of the deep mines.”
She looked at Giles, her eyes shining with pious zeal.
“You have given lungs to the stone, Lord Master builder! The breath of the righteous now drives the holy hearth.”
“It’s three point eight pounds of pressure of gage pressure, Teresa,” Giles said patiently. “Not a spiritual benediction. Toby, open the blast gate to the fire tuyeres.”
Toby Karr and two apprentice runners seized the iron handwheel of the main gate valve.
They spun the wheel with wild excitement. CLACK-CLACK.
The heavy brass gate lifted inside the sixteen-inch main air duct.
The tightly packed air surged through forty yards of underground sheet-iron piping, rushing into the double-walled copper tuyere nozzles embedded in the base of the forty-foot blast fire.
Inside the empty heat-proof crucible, forty feet of brick stack began to hum with a deep, ringing whistle, like a huge organ pipe sounding a single, underground note across the entire valley.
A crisp chime sounded in Giles’s vision, with the golden flicker of the system screen.
Captain Kenneth Drake marched up to the blower shed, with six mounted scouts of Torvald’s Dune-Striders.
He leaned his ten-foot pacing rod against the timber doorframe and looked up at the northern bluff road that led down from the mountain pass.
“Giles,” Kenneth said quietly, his voice cutting through the roar of the waterwheel. “We have company on the north ridge.”
Giles turned, pulling his pocket transit from his coat.
Sighting through the brass tube, he focused on the winding road that cut across the grey limestone cliffs two miles to the north.
Dropping the road was a splendid, four-wheeled traveling coach of dark blue lacquered oak, escorted by twelve heavy cavalrymen in burnished steel armor. Their lances fluttering with was dark blue and silver swallowtail pennants.
Emblazoned upon the coach’s door-panel was the proud heraldic crest of the northern realm. A silver rose entwined around an iron broadsword.
“The Iron Rose of Highmarch,” Kenneth muttered, his hand resting on his sword handle knob. “That isn’t a trade court guard, my lord. That’s the ducal carriage of Duchess Rowena Wintermere.”
Beside the carriage rode a woman in an elegant velvet riding coat, a fur-trimmed cap perched atop her auburn hair. It watched the smoking heavy-duty terrace with sharp, assessing eyes.
“Lady Beatrice of Dunwall,” Kenneth identified her, squinting through the river haze. “The Duchess’s chief political counselor and envoy. She has an eye for coin, and an ear for treason.”
“She has an eye for town productivity,” Giles corrected. He folded his transit and checking his watch. “The blast fire is scheduled to receive its first wood-pyre charge at four o’clock.
If the Duchess’s envoy wishes to witness the burden loading, she had better hurry. We don’t delay the smelting schedule for ducal pleasantries.”
Kenneth Drake adjusted his sword belt, looking down at the arriving carriage.
“Lady Beatrice doesn’t travel with twelve lancers for a simple neighborly call, my lord,” Kenneth said, his voice dropping low. “Duchess Rowena holds the northern mountain passes. If she believes Grey Crag is building siege engines, she may close the high roads before our grain arrives.”
“She won’t close the roads,” Giles replied calmly, folding his slide rule. “Highmarch is short of pig iron. Their smiths pay through the nose for imported southern metal bars. When Lady Beatrice sees ten tons of liquid metal pouring into sand runners every twenty-four hours, she will be calculating trade tariffs, not casualty lists.”
Toby Karr hurried to fetch his survey clipboard, wiping oil from his nose.
“Should I prepare the visitor seating on the charging platform, Lord Giles?” Toby asked.
“Set two stools by the crank winch, Toby,” Giles said. “And tell Sister Teresa to offer her hot chicory tea. Nothing calms high-born nerves quite like a warm mug and an overwhelming test of nonstop heat-powered throughput.”