The current Morrow Sluice plans arrived folded around a safety notice that was longer than the plans.
Civic Measures had approved a noncontact survey, provided we stayed outside the operating galleries, used no powered instrument, and did not interrupt the sluice’s water schedule. A second notice from the waterworks office prohibited placing equipment on the retaining walls. The plans themselves were stamped PRELIMINARY in three places and CURRENT in one, which suggested the office had a flexible relationship with time.
Ysabet laid them on the table in the Hall of Measures. “We can work with this.”
“You say that because you don’t have to make the readings agree.”
“I say it because the alternative is to stand here until the paper improves.”
Orren turned one corner of the sheet toward the light. “They’ve provided the rebuild plans, not the foundation survey.”
The old west foundation was marked in gray, overlaid by the present sluice in thick black lines. The new regulating chamber covered nearly all of it. An inspection passage ran along the north side, then stopped at a rectangle labeled SUBFOUNDATION—NO ACCESS. The note beside it read: bearing unresolved; verify during next dry service.
“Next dry service?” I asked.
“Whenever the river agrees to take a day off,” Orren said.
Ysabet tapped the lower edge of the plan. “We don’t need access. We need permission to measure from outside.”
She had put the request in as soon as we left the records room. I had expected a delay. The answer came the next afternoon, and the survey window was for the following morning, before the sluice’s scheduled regulator cycle. We were allowed to set instruments on the east service apron and the public maintenance walk, where the old line should emerge if it passed beneath the works.
That was enough to make the trip worth taking. It was not enough to make the result certain.
Morrow Sluice filled the valley between two steep, soot-darkened banks. Its iron gates stood beneath a roof of riveted beams, and a steady white breath drifted from the pressure vents. The river pressed against the upstream wall with a weight I could feel through the stone under my boots. Below the gates, water broke into a channel of foam and vanished under the city’s eastern embankment.
A maintenance foreman met us at the public walk. He had a grease pencil behind one ear and no patience for the plans.
“You can measure from the apron,” he said. “You can’t put anything on the wall, under it, or in the water. If the regulator starts its cycle, you clear the marked strip.”
Next
The alignment continues east beneath an area the current plans leave blank, and Merrit needs the missing District Seven sheet—and permission to survey beyond the embankment—to learn what it reaches.
The foreman looked at me. “You the one with the old bearing?”
“I’m the one who knows what it says.”
“That’s not the same thing.”
“No,” I said. “It isn’t.”
He seemed to like that answer less than an argument, but he let us through.
We set the survey frame on the apron, well back from the wall. It was a nonconductive tripod carrying a sighting bar, a mechanical level, and a set of passive vibration plates. No spellwork, no civic ward connection, no contact with the sluice. The plates could read tiny changes through the ground if the works didn’t shake them apart first.
Orren checked each foot before I set the level. “We have one hour before the cycle.”
“Fifty-six minutes,” Ysabet said, checking her watch.
“I appreciate the extra four.”
I aligned the first sight along the old bearing from the District Six sheet. The plan’s modern datum didn’t quite match the old survey grid, so I used the exposed points we had verified at the Hall of Measures as references. Ysabet read the coordinates while I adjusted the bar by fractions. The sluice rattled around us. A low hum came through the stone, too broad to be a single engine.
The first plate gave us nothing reliable. The second gave us a line that bent toward the middle of the works, where the old plan placed the alignment beneath the regulating chamber.
Then the nearest gate shifted. The sound changed; the water’s pressure settled into a deeper note. The needle on the plate jumped and stayed there.
“Cycle?” I asked.
“Not yet,” the foreman called from the marked strip. “Pressure equalization.”
The vibration ran through the apron and blurred the reading. I could wait for it to settle, but the alignment’s continuation was on the far side of the works. If the scheduled cycle started before we finished, the foreman would clear us out. We would have our permission, our plans, and no result worth carrying back.
I moved the second plate farther from the wall. The signal weakened but stopped wandering.
Orren frowned at the scale. “That’s outside the plan’s marked survey area.”
“It’s still on the service apron.”
“By a handspan.”
“Then the handspan will have to bear the moral weight.”
Ysabet looked at the foreman. He glanced toward the regulator housing, then gave a reluctant nod. “Keep it there. Don’t move closer.”
I reset the level. The reading steadied. One vibration plate registered the old bearing beneath the chamber; the second picked it up past the eastern face of the works, where no foundation mark appeared on the current plan. The signal was faint, but its direction held through three separate placements.
“Again,” I said.
We repeated the sequence. The alignment continued beneath the sluice and emerged east of the main structure, angling under the embankment. Not toward the open water. Not along the drainage channel. It crossed beneath the service road and went on, its course held by the same interval we had found beneath the Hall of Measures and at the boundary.
I checked the calculations. Ysabet checked mine.
“That’s a continuation,” she said.
“It’s a consistent bearing across the works. I can’t say what lies under the embankment.”
“But it doesn’t stop at Morrow Sluice.”
“No.” I looked at the old grid again. “It doesn’t stop here.”
The sluice began its cycle before we could take a fourth reading. A bell sounded from the regulator house, and the foreman pointed to the marked strip. We packed the plates and tripod while the first gate opened. The water’s roar filled the valley. For a moment, every measurement we had made seemed too small to matter against the force of it.
Then the second gate engaged. The apron shivered beneath my boots, and a loose bolt skipped across the stone. The foreman waited until we were behind the safety line before checking the pressure gauges. He had given us the time he could; the river had not agreed to give us more.
At the edge of the public walk, I wrote the survey result while it was fresh. Ysabet read the wording over my shoulder.
“‘The measured bearing is consistent with continuation beneath the east side of Morrow Sluice and toward the eastern embankment,’” she said. “Good. Don’t claim a route beyond the readings.”
“I’m not in the habit of making the ground say more than it does.”
Orren made a small sound. “You are in the habit of asking it rather insistently.”
“That’s how measurements work.”
We filed the survey notes with Civic Measures that afternoon. The result did not locate an opening or an endpoint. It established that the seven-stone alignment passed beneath an operating waterwork and continued beyond it—under ground the city’s current plans did not describe.
Ysabet had already attached a request for the District Seven continuation sheet, if it still existed. She added the Morrow Sluice result as the reason we needed it and asked for authority to extend the noncontact survey along the eastern embankment.
The request went into the docket. The plans went back to their folder. We had followed the line farther without laying a hand on the sluice, and the city had not needed to stop its water to let us do it.
I was pleased with that. I was also looking at the eastern embankment on the plan, where the measured bearing ran off the page into a blank space labeled MAINTENANCE LIMIT.
The old survey had once ended at a sheet edge. This time, the edge was only the boundary of what the city had chosen to draw.