“It does. But greater speed also gives it less time to act before the stone hits the target. By making the stone move more slowly, the weight that bends its path becomes weaker, but the extra time the stone spends in flight more than compensates for that.”
Zak was right. With the spring half-compressed, the stone emerged less rapidly, but the mark it made was shifted to the sard side of the Null Line by about twice the width of the stone itself. In a third experiment, with the compression reduced further, the sardwards shift was even more pronounced.
Roi could picture what was happening very clearly, now. While the stone was in flight, the Splinter was turning, carrying the wire and the target board a small way garmwards, leaving the un-rotated path of the stone to strike the target askew.
She said, “Why can’t we use this to measure the speed of the rotation?”
“It’s a crude experiment,” Zak insisted. “If I release the stone several times in succession with the spring compressed by exactly the same amount, the point where it strikes the target still varies. And how can I know how fast the stone is moving? It’s traveling too quickly for me to time its motion accurately.”
“Let it move more slowly, then. You’ll get a larger effect as well.”
“There’s a catch,” Zak said ruefully. “The more the stone gets pushed away from the Null Line, the more it comes under the sway of the ordinary garm-sard weight as well. What we’re measuring will no longer be one simple thing. When you combine that with the uncertainties in the aim and the velocity, I don’t think there’s much hope of getting a meaningful number out of the results.”
Roi could see how daunting the complications were, but she wasn’t ready to give up. “Can I try it? Slowly? Just to see what happens?”
“Of course.”
She squeezed the plunger down to the first notch, the smallest compression possible, then released it. The stone emerged at an absurdly leisurely pace, and even as she watched, it veered visibly sardwards. By the time it had traveled less than half a span toward the target its path had turned sideways, and not long after that it had swung around so far that it was level with the spring-shot again, albeit some distance sard of it. While continuing to move sardwards, its velocity along the Null Line had been completely reversed.
Roi said, “This is not what I’d expected.”
“It’s just following the rules,” Zak said.
Roi moved aside to let the stone pass her. Eventually, its sardwards drift seemed to level out, and it was simply moving backward, parallel to the Null Line, much faster than it had been moving when it had left the tube. Its direction continued to change, though; the relentless sideways tug of the weight of motion was stronger for this stone than it was for the wind, and it began to veer back toward the Null Line.
As the stone approached the Null Line, the sharqwards part of its motion slowed, leveled out, and reversed, so it was now heading back toward the spring-shot. This didn’t last long, though. When it reached the Null Line itself, almost grazing it, the stone executed a small loop that took it first sardwards, and then—in a replay of its original manoeuvre upon being launched—swung it around sharqwards once more. It was far behind the spring- shot, let alone the target, and showed no sign that it would ever come close to either again. Rather, it seemed to be cycling back and forth between the Null Line and a certain distance sardwards, while it drifted—mostly, though not constantly—ever more sharqwards.
Roi approached Zak. “What’s the simple explanation? I suppose I can accept that the sardwards weight combined with the weight of motion did all of that, but there must be an easier way to understand it.”
Zak said, “Think about the orbit of that stone. The stone was always on the sardside of the Null Line, so its whole orbit was larger than the orbit of the center of the Splinter. Larger orbits have longer periods, so the stone took longer than we did to go around the Hub. That’s why it drifted backward. It wasn’t as fast as us.”
“But it started out faster,” Roi protested.
“That’s true. At the same distance from the Hub, where its orbit touched ours, it was faster than us. That’s why we weren’t constantly outpacing it, and it didn’t move backward all the time. But over a complete orbit, we were faster.”
This made sense, but Roi still wasn’t satisfied. “Why didn’t the stones you launched go backward? Was that because they were moving faster than mine?”
“Definitely not!” Zak was emphatic. “The only difference was, they hit the target before they could swing around and go into reverse. If we had taken the target away—and the walls of the chamber too, if necessary—then those stones would have followed exactly the same kind of path as your one. The fact that they were moving faster made their paths larger, and we only saw a small part of each path, but other than that everything about them was the same.”
“I see.” The whole point of Zak’s version had been to concentrate on the very start of the motion, before the garm-sard weight could complicate things. “Can I try something else?”
“Anything,” Zak said.
She detached the spring-shot, then reattached it pointing in the opposite direction: sharq along the Null Line. Now the stone would be moving backward from the start, making it slower than the Splinter at the point where their orbits touched.
Its path followed exactly the same pattern as before, except that rarb became sharq, and sard became garm. After leaving the spring-shot the stone veered garmwards; halted its leisurely sharqwards progress and went rapidly into reverse; reached a maximum distance garmwards from the Null Line and started back toward it; then, close to the Null Line, performed a small loop that took it back into the same cycle, albeit many spans rarb of where it had begun.
Roi said, “Its orbit was smaller than ours, so it was racing ahead of us?”
“Yes.”
“And the way it moved away from the Null Line and then back again, that’s because the orbit wasn’t a perfect circle?”
“Right,” Zak said. “We remain a constant distance from the Hub, but there are orbits like this that draw closer to the Hub and then move away again.”
Roi contemplated this. “What if we could put a stone into an orbit that wasn’t a perfect circle, but was still the same size as ours, overall? With the same period?”
Zak didn’t reply immediately, but his posture made it clear that he was intrigued by her suggestion. “That could be very useful,” he said eventually. “We ought to see it execute a fixed, cyclic motion instead of running away across the chamber.”
Roi detached the spring-shot from the Null Line again, and attached it pointing sardwards: perpendicular to the Null Line, “halfway between” the two directions she’d already tried. She was acting purely on instinct, and even as she tightened the clips she wondered if launching the stone away from the Hub meant she’d be putting it into an orbit that would keep it perpetually on one side of the Null Line. But then, shooting the stone along the Null Line itself, which seemed more symmetrical in that respect, certainly didn’t work, so what she was trying made as much sense as anything.
She squeezed the plunger one notch, then released it.
The stone veered sideways as it emerged, but not as sharply as it had in the previous two experiments. As it moved, it picked up pace, but nowhere near as rapidly as before. Roi was surprised; she’d half expected the sardwards weight to take over and drag the stone into a frenzied spiral as the weight of motion twisted its ever- quickening flight. Instead, the stone continued to turn in a smooth, shallow arc, still progressing sardwards while swinging around ever more to the sharq.
Eventually, its sardwards motion leveled off, about two spans from the Null Line. It was moving perhaps three times faster now than it had when she’d launched it. It continued to swing around gently, coming back toward the Null Line, while its sharqwards speed lessened.
As it approached the Null Line, Roi tensed. It was no longer traveling sharqwards, but it would probably perform the same annoying little loop as the others, and then it would be lost to them, drifting away across the chamber.
It didn’t. It crossed straight over the Null Line, at about the same speed as it had left the spring-shot, and veered to the rarb. The symmetry was unmistakable: it was performing exactly the same kind of motion as it had when she’d fired it, only with garm in place of sard and rarb in place of sharq. If that symmetry held true, there was only one place where it could cross the Null Line again.
