Fun With Science / Globe Deconstruction / Earth Rotation
Question 11, the Compton generator, and the several thousand people who settle this for a living every day.
A spinning top is not stationary at its tip.
Answered dailyPremise invertedThe short version
The claim. A South Pole time-lapse shows no landscape turning under the camera; air at the axis has zero speed; no scientist has tested a Compton generator in Antarctica (Question 11, p. 54; the chapter behind it, pp. 179–194, argues a stationary Earth under a turning sky).
What is right in it. Surface speed at the axis really is zero, the air-speed table on p. 190 is correct to the mile per hour, and the book's own p. 182 argument — a body going in a circle “really is accelerating” — is the right test, because accelerated motion is detectable from the inside.
The verdict. Zero tangential speed is not zero angular rate. The pole turns in place at 15.04°/h, and local rotation experiments feel Ω sin φ — Earth's rotation rate Ω times the sine of the latitude φ — which is largest at the pole. A Compton generator reads 1.53× stronger at the South Pole than on Compton's bench in Ohio; a Foucault pendulum has been run at the pole (24 h ± 50 min against a predicted 23 h 56 m); north-seeking gyros fail there, as the same equation requires. A turning sky and a turning Earth look identical from a deckchair and different in a windowless room, where ships, tunnellers, drillers and airline crews measure the difference every working day. The ocean runs the experiment at every latitude: fifteen NOAA drifters return the length of the day to within half a per cent.
The chapter is arguing geocentrism: not that nothing rotates, but that the relative rotation everyone agrees on belongs to the sky rather than to us. p. 180 quotes Einstein to that effect — the Sun at rest and the Earth moving, or the reverse, are “two different conventions concerning two different” coordinate systems. For steady straight-line motion that is correct, and it is why nobody can feel the Earth's orbit. But p. 182 supplies the reason it does not extend to spin: relativity of motion “only applies to constant straight-line speed,” and a body going in a circle “really is accelerating.” That is right, and it cuts cleanly:
Rotation is accelerated motion. Accelerated motion is detectable from the inside. So if the Earth turns, it must be possible to prove it in a sealed room — and if the sky turns instead, it must not.
A rotating sky exerts nothing on a pendulum, a gyroscope or a bucket of water in a basement. A rotating Earth puts everything on it in a rotating reference frame, where centrifugal and Coriolis effects appear whether or not anybody is looking, with a size, direction and dependence on latitude that can be checked against a formula. The question is whether the turning shows up somewhere the sky cannot reach. (The strongest geocentric reply, which is not the chapter's, is taken up at the end; it does not change what follows.)
Several trades depend on Earth's rotation being real and quantitatively correct, and almost none of them can see the sky while they work.
Free-floating ocean drifters trace small circular loops on top of whatever current carries them — inertial oscillations, the same physics the instruments above exploit — with a period that depends on latitude and a direction that depends on hemisphere. Fifteen NOAA drifting buoys, deployed for weather and climate work by people not arguing with anybody, give this:
A stationary Earth under a turning sky predicts no loops at all. A flat turntable predicts loops of identical period and direction everywhere, with nothing happening at the equator. A spinning sphere predicts what is observed. And a float has no sensitive axis, no calibration and no bias term; it reports where it is, and the rotation is in the shape of the path.
The discriminating factor in the drifter data is the trend line, not the final point.
No individual buoy proves anything. Any one reading could be a poorly-resolved spectrum or a float shifted off the predicted period by the spin (vorticity) of the current it rides in — two of the fifteen are well out for that kind of reason — and near 30° of latitude, where the inertial period is about 24 hours, a single loop can be called tidal. What cannot be a coincidence is fifteen floats lying along a one-parameter curve and reversing handedness at the equator; tidal periods are fixed and do not scale with sin φ. The constant is over-determined fifteen times, which is why the fit recovers the length of the day rather than merely being consistent with it — and why a polar reading is unnecessary. A rotating globe predicts a specific value at every latitude with one constant and no freedom to fit; the pole is where the curve runs out of hemisphere. The measurement has been made from 63°N to 59°S, it traces the predicted curve, and the extrapolation to the pole is arithmetic.
Question 11 is a summary; the chapter runs pp. 179–194. A table on p. 190 gives air speeds of 1,040 mph at six feet rising to 1,050 mph at 37 miles, objecting that “the higher layers of air would have to travel mechanically faster to keep up.” p. 191 asks whether synchronised rotation happens “at all points of the ball — 0 mph air speed at axis.” p. 192 puts it most directly: “At the exact axial point, what makes a drone rotate in sync with the ground if it is not attached to it?” The Compton generator appears once in the book's five hundred pages, in Question 11, and is never defined. So that comes first.
A hollow ring of tubing, filled with water and sealed. Arthur Compton built the first in 1913, as a final-year undergraduate at the College of Wooster in Ohio, from one-inch brass tube bent into a circle eighteen inches across, with droplets of coal oil in the water and a microscope on a viewing window. Lay it flat, let the water settle, then flip it through 180° about a horizontal diameter. Flat, the water was turning with the Earth at Ω sin φ; flipped, the tube turns at −Ω sin φ while the water's angular momentum is unchanged, so relative to the tube it circulates at twice the original rate until viscosity kills it. A Foucault pendulum with the bob replaced by a fluid:
ū = 2ΩR sin φ
Note the sin φ: zero at the equator, maximum at the poles. Compton's nine-inch-radius ring gives 21.8 µm/s at Wooster and 33.3 µm/s at the South Pole — 1.53× stronger. The 1913 Science paper is a demonstration; the precision came in 1915, in Physical Review, under a title that says what it is for — “A Determination of Latitude, Azimuth, and the Length of the Day Independent of Astronomical Observations”: latitude to about 3%, and the length of the day to within roughly sixteen minutes, about one per cent, from a sealed ring of water on a bench. Those two figures come from secondary summaries of the 1915 paper, which we have not been able to read; treat them as approximate.
“The rotational speed of the air at the axis point would be zero” is true of one quantity and false of another.
| At the equator | At the pole | |
|---|---|---|
| Tangential speed across the surface | ~1,040 mph | 0 |
| Angular rate | 15.04°/h | 15.04°/h |
| Vertical component Ω sin φ — what local experiments feel | 0 | maximum |
A rigid body turning about an axis has the same angular velocity throughout; only distance from the axis, and so linear speed, varies. The pole does not stop rotating — it rotates in place.
Earth's rotation resolves into two local components, and they behave oppositely with latitude:
| Component | At the equator | At the pole | What depends on it |
|---|---|---|---|
| Vertical, Ω sin φ | zero | maximum | Foucault pendulum, Compton generator, inertial loops |
| Horizontal, Ω cos φ | maximum | zero | gyrocompasses and gyrotheodolites finding north |
So a spinning Earth predicts that at the pole, pendulums and water rings read their strongest — and north-seeking gyros stop working entirely. Both are observed. A gyrotheodolite cannot be used at either pole, and is unreliable above about 75° latitude, because the angle between Earth's rotation and local gravity becomes too small to resolve: an operating limit that mine surveyors plan around.
The argument runs: at the axis the air has no speed, so a camera up in it is not dragged around by anything; if the ground were rotating, the camera should hold its heading while the landscape turned beneath it; no turning is seen; therefore it is not turning. Every step follows, provided the camera is genuinely decoupled from the Earth. On the ice, camera and landscape are bolted to the same rotating object and share its motion exactly, at the pole as in Reykjavík or Nairobi. Airborne, the air is not stationary either: the polar air column turns in place at 15.04°/h and carries anything floating in it, and a drone holds heading with a magnetometer nearly useless at the pole and a chip-scale (MEMS) gyro whose heading drifts by degrees an hour — sensors that cannot resolve 15°/h, let alone subtract it. Genuinely decoupled, on a mount holding fixed orientation in space, the prediction is correct: the landscape really would turn beneath it, at 15.04°/h, which is 0.25° per minute. Across a twenty-to-forty-minute drone flight that is five to ten degrees, which nobody notices by eye in a shaky aerial shot.
The effect is real and slow and the eye is the wrong instrument. Put something sensitive enough on that decoupled mount and it registers immediately — which is what a ring-laser gyroscope is, and why the chapter must then spend pp. 183–187 arguing those instruments measure something else.
In the winter of 2001, Mike Town (University of Washington), John Bird (York University) and R. Allan Baker (Sonoma State) hung a Foucault pendulum down the six-storey stairwell of the new Amundsen–Scott South Pole Station while it was under construction — a 33 m wire carrying a 25 kg bob, in a sealed shaft where no moving air could disturb it. They measured a precession period of 24 hours ± 50 minutes against a predicted 23 h 56 m, with the swing plane drifting counter-clockwise across the floor, the mirror image of the northern hemisphere, and got g = 9.85 ± 0.03 m/s² along the way. Their account is here, posted to Baker's university page in October 2001.
The Compton generator itself is a 1913 teaching demonstration accurate to about 1%; ring-laser gyroscopes now measure the same rotation continuously to parts in 10⁸. The modern separating test is Compton's — rotate the instrument 180°, and the Earth signal reverses sign while instrument bias stays put — in daily industrial use, no longer made of brass and water.
Question 10 asks how it was established that air layers “stay in perfect rotational sync across all heights of the atmosphere,” and p. 190 puts numbers to it: 1,040 mph at six feet, rising to 1,050 mph at 37 miles, which is said to go “against demonstrable engineering principles.” Speed is angular rate times radius, and checking the figures gives 1,039.2, 1,041.9, 1,044.8 and 1,049.0 mph. Two things follow that the chapter doesn't consider.
The whole difference is 9.7 mph spread over 37 miles of altitude — about a quarter of a mile per hour per mile of climb.
| Wind shear | Change per mile of altitude |
|---|---|
| Required by co-rotation | 0.26 mph |
| An ordinary jet stream | ~20 mph |
Everyday weather sustains vertical shear roughly 75× larger than anything co-rotation demands, in every frontal system, on every continent. Whatever principle is supposed to forbid the smaller number has to explain why the larger one happens daily.
The word doing the damage is “keep up.” It pictures a ground that has started spinning and an atmosphere scrambling to catch it. Nothing is catching anything: uniform rotation requires no force to maintain, the air has been turning with the planet since both condensed, and angular momentum is conserved. No principle says a fluid cannot rotate with the body it rests on; one says it will carry on doing so unless something stops it.
The stronger answer is to reject the premise. The atmosphere is not in perfect rotational sync, nothing in the standard model says it is, and the departures are the subject matter.
Air that lags the surface is an easterly wind. Air that runs ahead of it is a westerly. Every weather map is a map of the atmosphere failing to co-rotate.
The trade winds are air lagging the surface in the tropics; the mid-latitude westerlies are air running ahead of it. Jet streams are departures of 100 to 250 mph, ten to twenty times the entire co-rotation gradient in his table. Higher still, the thermosphere genuinely super-rotates, faster than the ground beneath it. And the pattern of departures is the drifters' signature in a different fluid. Through the lowest kilometre or so of atmosphere — deeper in strong winds, shallower in calm — friction couples the air to the ground and the wind direction turns with height: clockwise going up in the northern hemisphere, anticlockwise in the southern. This is the Ekman spiral, it is in the opening chapters of every meteorology textbook, and weather balloons measure it twice a day from roughly 800 stations worldwide.
A fibre-optic gyroscope reportedly read differently at different altitudes on the same line of latitude — “more than a full degree per hour” between Pike's Peak at 14,115 ft and the Eastern Plains at 4,000 ft — taken as showing the instrument is not measuring Earth's rotation at all. The globe model does predict no altitude dependence, so that part is stated correctly; the question is whether the measurement is. The book says plainly that the data is unsourced — p. 187: “I could not find the formal document with their exact measurements. We need multiple teams to perform this to see if the results are true” — so by its own author's assessment the table is the weakest evidence in the chapter.
Two ordinary things would produce the reported variance. Mounting tilt: a gyroscope with its sensitive axis vertical reads Ω sin(φ + tilt), and at 38.84°N the true signal is 9.433°/h with a sensitivity of 0.204°/h per degree of tilt. Under five degrees of tilt reproduces the entire claimed effect, and levelling to better than a degree on a mountain summit, in cold and wind, does not happen by default. A 10,000-foot altitude change also brings a large temperature swing, the other thing fibre-optic gyro bias tracks. And the control is not clean: the table lists Guanella Pass at 39.59°N against 38.84°N for the other two sites, which alone predicts about 0.15°/h of variance.
The alternative on offer predicts the wrong pattern. If these instruments sense a vortex in some medium rather than the rotation of the ground, the signal should vary with altitude and have no reason to track latitude. The world's large ring lasers show the reverse: at wildly different elevations — Wettzell in Bavaria at around 610 m, the Cashmere cavern at Christchurch near sea level — each reads Ω sin φ for its own latitude, continuously, the Wettzell G ring to parts in 10⁸. The claimed effect is on the axis where the data is flat; the axis where the data is not flat goes unmentioned.
The table follows up the most widely seen gyroscope result in this dispute: in the 2018 documentary Behind the Curve, a flat-Earth team put a ring-laser gyroscope on a bench and found it drifting at 15° an hour, the rate a rotating Earth assigns, on their own instrument. The book's position (p. 185) is that the film stopped the story halfway, before the altitude work; take that at face value and the answer is the one above — a rotating Earth predicts the 15°/h, predicts it to vary as sin φ and reverse sign across the equator, and predicts no altitude dependence; a stationary Earth predicts zero. The equator-flight page takes the Behind the Curve reading, and the light-medium vortex offered in its place, in full.
The book lists reasons Foucault pendulums are hard to run: an elliptical swing precesses on its own through Airy precession, a suspension stiffer in one direction biases the path, temperature changes the wire, draughts push the bob, traffic vibration distorts it, and a misaligned electromagnetic drive can steer a museum pendulum into a false rate. Every one of those is true. What none of it explains is why the artifacts should trace a curve. Those error sources bear no relationship to latitude; the precession rate does — it follows sin φ, from 36.6 hours at Compton's Wooster to 26.6 at Reykjavík to 23.93 at the pole. A stiff suspension does not know what latitude it is at.
One note on the source. The book cites Heike Kamerlingh Onnes's 1879 doctoral thesis as documenting why these pendulums fail. That thesis is titled “Nieuwe Bewijzen voor de aswenteling der aarde” — “New Proofs for the Axial Rotation of the Earth.” Onnes catalogued the error sources so the experiment could be done properly; the work reaches the opposite conclusion to the one it is cited for. (His Nobel came in 1913, thirty-four years later, for liquefying helium.)
The gyroscope chapter argues against one instrument. Earth's rotation has been detected by at least five mutually unrelated physical mechanisms — a spinning mass, the Sagnac effect on light (light sent both ways round a closed loop returns out of step if the loop is turning), the Coriolis force on a vibrating structure, the Sagnac effect on matter waves, and quantum phase coherence in superfluid helium — with no shared calibration chain and no common scale factor. The crudest result is a few per cent and the best is parts per billion, six orders of magnitude apart, with no disagreement anywhere. A systematic error that faked rotation in a ring laser would have to fake it again, at a differently-scaled phase, in caesium, in superfluid helium and in a brass gyrocompass with no scale factor at all.
What we are not claiming. Nuclear-spin (NMR) gyroscopes are sensitive enough — bias instabilities of 0.01 to 0.04 °/hr against Earth's 15.04 °/hr — but we could find no published measurement of Earth rate by one, so they are left out; comagnetometer experiments subtract Earth's rotation as a modelled term taken from VLBI (very-long-baseline radio interferometry) and ring lasers, a consistency check rather than an independent one. Most of these papers report agreement with the accepted figure rather than a standalone value with an error bar: all five agree with the IERS (International Earth Rotation and Reference Systems Service) value of 15.04107 °/hr within their stated uncertainties, not all five independently returned it. Lumping all interferometry as one idea and all rotating-frame mechanics as another, the count falls to three: Newtonian mechanics, wave interference, and macroscopic quantum coherence. Three is still three.
The ordinary version is stronger than the exotic one. Merchant ships find true north with a gyrocompass, which works only because the Earth turns. The international performance standard, IMO Resolution A.424(XI), sets the permitted settle-point error at ±0.75° multiplied by the secant of the latitude (1/cos φ): north-seeking torque goes as Ω cos(latitude), so the error must scale as its reciprocal. Modern fibre-optic and resonator gyrocompasses are specified the same way, at 0.1° and 0.08° secant latitude. A stationary Earth predicts nothing of the sort, and the formula has been in maritime law since 1979.
“A rotating sky exerts nothing on a pendulum” is a Newtonian claim. In general relativity rotating matter drags the local inertial frame with it — the Lense–Thirring effect, measured by Gravity Probe B and by satellite laser ranging — and a sophisticated geocentrist (Sungenis and Bouw both go here) argues that a rotating shell of distant matter would drag the frame inside it, so that Foucault, Coriolis and the drifter loops are what that dragging feels like from the inside. Earth's own frame dragging, about 39 milliarcseconds a year against the 15° an hour to be accounted for, is not the fair reply: Brill and Cohen showed in 1966 that a rotating shell drags the interior frame almost completely as its mass approaches its own gravitational radius, which the observable universe roughly satisfies. What is missing is a worked solution — no general-relativistic cosmology has been shown to reproduce an Earth frame turning at 15.041°/h by a rotating universe, and Bondi and Samuel found the answer depends on which of ten statements of Mach's principle you adopt.
It is a real objection, and for the chapter it is an own goal twice over. It concedes the physics the chapter disputes: the Machian version predicts exactly the Coriolis and centrifugal terms the instruments measure, and argues only about which frame deserves the label “really rotating.” And it needs a sphere: the sin φ law, the equatorial null and the hemisphere sign flip come from the geometry of the surface the instrument stands on, and no rotating-sky-over-a-flat-disc arrangement produces them. Everything on this page measures the relative rotation and finds it real, quantitative and shaped like a sphere; which frame is “truly” turning can be left open, because either answer costs the chapter its conclusion.