The Mechanical Clock

The History of Timekeeping

Course 2 · Chapter 4 · The Mechanical Clock

The word "clock" comes from the same root as the French cloche and the Latin clocca, a bell (check the derivation). That is a clue to what the first mechanical clocks were for. They did not, at first, have faces or hands. They struck a bell, to call monks to prayer or townspeople to work, and the sound mattered more than the sight. This chapter follows the invention that made them possible, the escapement, describes how the earliest clocks worked, and traces their spread from monasteries to town squares and, in time, to the home.

The Problem to Solve

A falling weight, pulling on a rope wound round a drum, can drive a train of gears. The difficulty is that a weight simply falls: left to itself it would drop to the floor in a rush. To make a clock, the energy has to be released in small, equal steps. The device that does this is the escapement.

The key idea An escapement lets a toothed wheel advance one tooth at a time, each time with a small "tick", while a regulating part swings back and forth to control the pace. The invention of the escapement, probably in Europe in the late thirteenth century, is the point at which the mechanical clock becomes possible (check the date and place). Nobody knows who devised it, and any named inventor is a legend or a guess (check).

The Verge and Foliot

The earliest known escapement is the verge, sometimes with a balance bar called a foliot.

The crown wheel

A wheel with pointed teeth, turned by the falling weight through a train of gears.

The verge

A vertical rod with two small flags, the pallets, set at an angle so that one tooth is caught as another is released.

The foliot

A horizontal bar fixed to the top of the verge, with small weights at each end. Moving the weights in or out changes how fast it swings and so how fast the clock runs.

The weakness was that the foliot had no natural rhythm of its own. Its speed depended on the force driving the clock, and so on friction and on the state of the gears. These clocks were commonly out by a quarter of an hour or more a day (check the figure), and keepers set them against a sundial at noon.

Early Clocks in Records

Place and period	What the record shows
Italy and England, late 13th century	Documents suggest early clocks, often in religious houses; it is not always clear what kind of device they were (check)
Milan, around the 1330s	A public striking clock is mentioned (check)
Salisbury Cathedral, 1386	A clock with a verge escapement and no dial, often cited as the oldest working example in England (check the details)
Padua, around 1360s	An astronomical clock made by Giovanni de Dondi, with a display of the planets (check)
Wells and Exeter, 14th century	Cathedral clocks with astronomical dials, parts of which survive (check)

What "oldest" means Claims that a clock is "the oldest in the world" usually depend on a definition: oldest working, oldest surviving in its original form, or oldest with a documented date. Most old clocks have been repaired, converted or had parts replaced over centuries. When you see a claim of this kind, ask which definition is being used.

Clocks in the Town

By the fourteenth and fifteenth centuries, cities across Europe were building public clocks, and the reasons were not only religious. A town clock was a matter of civic pride and of civic order.

Working hours. A bell told craftsmen and market traders when to start and stop, and employers and workers sometimes quarrelled over whose time it measured (check).
Markets and courts. A public time made it possible to fix the opening and closing of a market or the hour of a hearing.
Prestige. Towns competed to have the grandest clock, with moving figures, astronomical dials and processions of statues. Prague's astronomical clock, begun around 1410, is a famous example (check).
Standard hours. As clocks spread, equal hours of the same length all year round replaced the seasonal hours of Chapter 2 in daily life.

Dials came later than bells Many early clocks had no dial at all and simply struck the hours. Dials and hands, and the hour hand in particular, became common in the following centuries, and the minute hand only became useful once clocks were accurate enough to justify it, which took the pendulum (Chapter 5).

Springs and Smaller Clocks

A weight-driven clock must be fixed in one place and needs a tall case or tower to give the weight room to fall. The coiled spring, in use by the fifteenth century (check), made smaller, portable clocks possible, and in time watches. The early spring-driven clocks had a problem of their own: a spring pulls harder when fully wound than when nearly run down, so the clock sped up and slowed down. A cone-shaped pulley called a fusee, which evened out the pull, was the answer (check the date). Nuremberg in Germany was known for its early small portable timepieces (check).

Exercises

Exercise 1

In four sentences, explain what an escapement does and why a falling weight alone cannot run a clock.

→ Solution

Exercise 2

Imagine you are a cathedral official in the fourteenth century deciding whether to buy a mechanical clock. List three arguments in favour and two against, using what you know of the alternatives (sundials, water clocks, candles).

→ Solution

Exercise 3

Find a public clock near you (a church, a town hall or a station). Note whether it has a dial, a bell or both, and write two sentences on what you can find out about its age and whether it is the original mechanism.

→ Solution

Quick Reference

Clock and bell: early clocks struck bells; many had no dial
Driving force: a falling weight (later a coiled spring)
Escapement: releases the energy in small, equal steps
Verge and foliot: the first escapement; simple, but poor accuracy
Early examples: Salisbury (1386), Milan, Padua, Prague
Spring and fusee: allowed smaller clocks; the fusee evened out the pull
Equal hours: spread with the public clock
Check: the date of the escapement, "oldest" claims, the dates and details of the named clocks

Next chapter: The Pendulum and Precision, which covers Galileo, Huygens, the anchor escapement and the clockmakers of Britain.