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IVTime in the Pocket

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ESEN
Index

Chapter IV · Act I — Reading Time

Time in the Pocket

16th century – 17th century

Time becomes personal, and precision takes its first great leap.

A coiled spring takes the place of the weight, and the clock can travel. But a spring pulls hard when freshly wound and weakly at the end, and a clock given more force runs faster. Since the fifteenth century, one part has evened that force out: the fusée.

The mainspring and the fusée

Spring 100 % · train 100 %

Drag to turn it · arrow keys on a keyboard · double-click to face it

Mainspring and fusée. The fusée’s profile is calculated so the force on the train stays constant; the spring’s loss of force is illustrative. The oldest surviving clock with a fusée is one from Burgundy, of about 1430.

  1. 1Barrel
  2. 2Mainspring
  3. 3Cord or chain
  4. 4Fusée

  1. Freshly wound, the mainspring presses its coils round the arbor and pulls with all its strength.

  2. A gut cord carries that pull to the fusée, a cone cut with a spiral groove. From about 1650 a chain begins to replace it, as it lasts longer.

  3. While the spring is strong the cord pulls on the small radius; when it is weak, on the large one. Like a lever that grows longer.

  4. Take the fusée away: without it, the force on the train falls with the spring, and the watch changes rate through the day.

The myth

Peter Henlein invented the pocket watch in Nuremberg around 1510, and his watches were called “Nuremberg eggs”.

What the sources say

Henlein, a Nuremberg locksmith, was making small iron clocks by about 1511 that struck the hours for forty hours without weights, but nothing proves he was the first. The “eggs” come after his death: in 1571 a translation wrote Eierlein, “little egg”, for Ueurlein, “little clock”.

Christiaan Huygens invents the pendulum clock on Christmas Day 1656 and patents it the following year; the clockmaker Salomon Coster builds them. Precision takes its first great leap.

≈ 15 minof error a day, the best foliot clock

≈ 15 sof error a day, the pendulum clock

Personal time

  1. c. 1550

    Geneva and the banned jewellery

    Calvin forbids the wearing of jewellery, and Geneva’s goldsmiths and jewellers turn to watchmaking, helped by Huguenot refugees. In 1601 the watchmakers found a guild of their own.

  2. c. 1582–1602

    Galileo and the pendulum

    According to his pupil Viviani, a lamp swinging in Pisa Cathedral shows him that a pendulum takes the same time for every swing, wide or narrow. He puts it in writing in a letter of 1602. It holds only for short swings, as Huygens will show.

  3. The waistcoat

    Charles II of England sets a new garment at court, the waistcoat, as Samuel Pepys notes on 8 October. The watch, worn until then round the neck or pinned to clothing, moves into the pocket; tradition dates the change to 1675.

  4. The anchor escapement

    The oldest clock to have one, at Wadham College, Oxford, dates from 1670. It is credited to William Clement, and sometimes to Robert Hooke. It cuts the pendulum’s swing from some 90° to some 5°: pendulums a metre long, beating seconds, fit in tall cases.

  5. The balance spring

    Huygens gives the pocket watch a pendulum of its own: a spiral spring joined to the balance, built by Isaac Thuret. Hooke disputes his priority. The error falls from several hours a day to some ten minutes, and from about 1680 English watches gain a minute hand.

The Line of Precision

The error a day of each chapter’s clocks, on a logarithmic scale. The line moves on with the story: each chapter draws its own stretch.

This chapter’s precision

Huygens’s pendulum1656
≈ 15 s a day
  1. c. 1390 BCE: Clepsydra, ≈ half an hour a day
  2. c. 1386: Foliot tower clock, ≈ 15 min a day
  3. 1656: Huygens’s pendulum, ≈ 15 s a day

This chapter’s sources