Tom Johnson:

Clockmakers, flush with commissions, let their horological imaginations run wild. They mounted every last thing they could think of on their clocks: trumpeting angels, wheels of fortune, planets and stars wheeling around in epicycles – take that, astrolabe – and panoplies of bells to add to the din of holy clanging. The still-extant clock of Wells Cathedral, constructed about 1390, is a carnival of time. A face of three concentric circles shows the 24 hours, the position of the sun and the phases of the moon, all decorated with stars, angels and depictions of the four cardinal winds. Every fifteen minutes, four knights come out to joust. Above the clock an automaton (‘Jack Blandifer’) kicks his heels on bells every quarter hour. In the 15th century an exterior clock was geared onto it: two axe-men stand and strike two more bells on the hour. Nequid pereat, runs the inscription – let nothing perish, no matter how whimsical. 

Here is the marvelous clock of Wells Cathedral: 

(Larger version, well worth inspecting, here.) And here, at least as admirable, is Simon Armitage’s glorious poem “Poetry”: 

In Wells Cathedral there’s this ancient clock,
three parts time machine, one part zodiac.
Every fifteen minutes, knights on horseback
circle and joust, and for six hundred years

the same poor sucker riding counterways
has copped it full in the face with a lance.
To one side, some weird looking guy in a frock
back-heels a bell. Thus the quarter is struck.

It’s empty in here, mostly. There’s no God
to speak of — some bishops have said as much —
and five quid buys a person a new watch.
But even at night with the great doors locked

chimes sing out, and the sap who was knocked dead
comes cornering home wearing a new head.