MUJCA

The complete register

All nineteen entries

Every mechanism on this site, grouped by section, with the error each one was built to defeat.

I · Longitude

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A large ornate pocket watch movement displayed under glass in a museum case, dial removed to show the mechanism, controlled gallery lightingHarrison's H4Finished in 1759 and now at the Royal Observatory, a large watch that kept time well enough to find longitude across an Atlantic crossing.An antique brass sextant on a chart table beside a chronometer in its box, window light from the leftWhy longitude is timeThe Earth turns fifteen degrees an hour, so knowing the time at a reference place tells you how far around you are.A gimballed marine chronometer in its wooden box, lid open, on a wooden surface, hard side lightThe sea defeats a clockRoll, damp, salt and temperature swings break every assumption a room clock makes.

II · Escapement

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Extreme close on an anchor escapement engaging an escape wheel, pallets and teeth sharp, everything else falling awayWhat an escapement doesIt releases the train one tooth at a time and returns a push to the oscillator, doing two jobs that fight each other.A precision regulator clock movement seen from the front with the dial off, deadbeat escapement at the top, even lightThe deadbeatGeorge Graham's escapement stopped the recoil that pushed the pendulum back and improved rate immediately.A watch movement with the balance and lever visible, photographed through a loupe, shallow depth of fieldThe leverThomas Mudge's escapement is in almost every mechanical watch made since.A wooden clock movement with unusual pivoted arms, museum display, soft lightThe grasshopperHarrison's near-frictionless escapement needed no oil, which is why his clocks kept running.

III · Compensation

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A gridiron pendulum of parallel brass and steel rods hanging in a longcase clock, seen straight on, dim interiorThe gridironAlternating brass and steel rods expand against each other so the pendulum's length stays put.A cylindrical glass jar of mercury mounted as a pendulum bob inside a clock case, close, low lightMercury and invarA jar of mercury rising as the rod lengthens, and later an alloy that barely moves at all.A cut bimetallic balance wheel with timing screws around the rim, macro, dark groundThe bimetallic balanceA split rim of two metals curls with temperature and moves the mass inward.

IV · Free Pendulum

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A tall cylindrical vacuum tank containing a pendulum, mounted on a wall in an observatory basement, cold even lightThe Shortt free pendulumTwo pendulums, one doing nothing but swinging in vacuum while a slave does the work — accurate enough to reveal irregularities in the Earth's own rotation.A sealed glass and metal vacuum vessel with a valve and gauge, workshop bench, hard lightWhy vacuumAir resistance and changing barometric pressure both change the rate.An observatory transit instrument in its housing, aligned north, shafts of daylightMeasuring the EarthWhen the clock beat the planet, the planet turned out to be the unreliable one.

V · Quartz

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A tiny quartz tuning-fork resonator out of its can, on a white surface beside a sewing needle for scale, macroThe crystalA quartz sliver vibrates at a frequency set by how it is cut, and it is far more stable than anything mechanical.A drawer of small mechanical watch movements in labelled trays, overhead light, workshopWhat quartz cost the tradeAccuracy became cheap almost overnight, and an entire industry had to argue for itself on other grounds.A quartz crystal blank held in tweezers under a bench lamp, macro, dark backgroundTemperature againQuartz has its own thermal curve, which is why the cut angle matters so much.

VI · The Bench

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A row of similar marine chronometers in fitted boxes on a shelf, museum store, even lightArnold and EarnshawThe two who made the marine chronometer producible rather than a single miracle.A watchmaker's lathe on a bench with gravers laid out in order, warm task lightThe toolsA watchmaker's lathe, a depthing tool and a set of gravers do work no machine replaced for a long time.A clock dial with an engraved retailer's name, photographed square on, raking light picking up the engravingWho gets the nameThe name on the dial was often the retailer, not the maker.