The Shibboleth of Science is "That's Odd"
“Academician. Academician.” The foundry master wiped his hands on his leather apron, and waved at the looming bulk in the back of the workshop. “Your sky-tube’s coming along to plan. Just got the wire-wrapping on today. The woodwright’s’ll be here tomorrow to get the quarter-boards on her, and your chymist seems satisfied. Though I’d appreciate it if you’d have him do the filling elsewhere; the way he was talking, that stuff you’re using shouldn’t be within a mile of our fire-works.”
“It shouldn’t, or most other places, indeed. We’ll not be filling her until we’re in place to fire her. And we should, then, be ready to take delivery by the 19th?”
“We’ll have her ready for you. What’s all this about, anyway? I’ve built the like before, but nothing half this large.”
“We’re going to find out where gravity breaks.”
“Ah…”
“It’s one of the more troubling problems in natural philosophy,” the second Academician put in. “The difference between Celestial and Terrestrial Gravitation. You see, ever since records began at the Starspike, and it was shown that…”
“We don’t need all three thousand years,” the first interrupted.
“Um, yes, anyway, after a lot of observation and even more theorizing, most of it wrong, the Starspike’s skywatchers figured out that the planets, and us, and the Shining One, and its planets, and all the moons are all moving around each other in lovely, sweeping ellipses as they fall together and always miss. And after much computation, Siao Callaneth produced his Lemmas and declared that if you postulate an attractive force that’s in proportion to their masses and inversely proportional to their distances, all the numbers come out right.”
“Yeah, but that’s true down here, too. We use his lemmas all the time in structures.”
“Ah, but it’s only true sometimes down here. Up there, if you assume that a world is a point, it works. Down here, if you assume that an object is a point –”
“If it’s homogenous, otherwise it’s an offset point.”
“If it’s homogenous, yes, thank you, it works. Between objects, if you have heavy objects and sensitive pendulums. But if you drop something here, what direction does it fall?”
“Down?”
“Down, yes. Straight down. And we’re not above the center of the world, are we? But if we drop something, anywhere, it falls in a nice straight line perpendicular to Eliéra’s notionally-flat surface, even though the center of all the world’s mass is thousands of miles over there. It falls straight down here, it falls straight down in Mossstone, it falls straight down even in heathen Indimór-on-the-Rim, for all that the Lemmas say that the world’s gravity should drag everyone there sideways off their feet, if not crumple the edge of the world up like tissue paper, rock not being all that strong. And that is Terrestrial Gravitation, the damned exception that’s been inexplicable ever since the Shadow-watcher made note of it when proving the world was flat in the first place.”
“Eliéra behaves both ways, you see. Down here, things fall straight. But if it behaved that way celestially, we’d orbit – well, we wouldn’t move in one of those beautiful ellipses, and the moons probably wouldn’t stay up. Somewhere, if you go far enough up, everything changes. And watching Skybreaker here fly is going to tell us where.”