The word horologia (from the Greek ὡρα, hour, and λέγειν, to tell) was used to describe all these devices, but the use of this word (still used in several Romance languages) for all timekeepers conceals from us the true nature of the mechanisms
For example, there is a record that in 1176 Sens Cathedral installed a ‘horologe’ but the mechanism used is unknown
According to Jocelin of Brakelond, in 1198 during a fire at the abbey of St Edmundsbury (now Bury St Edmunds), the monks 'ran to the clock' to fetch water, indicating that their water clock had a reservoir large enough to help extinguish the occasional fire.
A new mechanism
The word clock (from the Latin word clocca, "bell"), which gradually supersedes "horologe", suggests that it was the sound of bells which also characterized the prototype mechanical clocks that appeared during the 13th century in Europe.
Outside of Europe, the escapement mechanism had been known and used in medieval China, as the Song Dynasty horologist and engineer Su Song (1020–1101) incorporated it into his astronomical clock-tower of Kaifeng in 1088. However, his astronomical clock and rotating armillary sphere still relied on the use of flowing water (i.e
hydraulics), while European clockworks of the following centuries shed this old habit for a more efficient driving power of weights, in addition to the escapement mechanism.
A mercury clock, described in the Libros del saber, a Spanish work from AD 1277 consisting of translations and paraphrases of Arabic works, is sometimes quoted as evidence for Muslim knowledge of a mechanical clock
However, the device was actually a compartmented cylindrical water clock, whose construction was credited by the Jewish author of the relevant section, Rabbi Isaac, to "Iran" (Heron of Alexandria).
Between 1280 and 1320, there is an increase in the number of references to clocks and horologes in church records, and this probably indicates that a new type of clock mechanism had been devised
Existing clock mechanisms that used water power were being adapted to take their driving power from falling weights
This power was controlled by some form of oscillating mechanism, probably derived from existing bell-ringing or alarm devices
This controlled release of power - the escapement - marks the beginning of the true mechanical clock.
These mechanical clocks were intended for two main purposes: for signalling and notification (e.g
the timing of services and public events), and for modeling the solar system
The former purpose is administrative, the latter arises naturally given the scholarly interest in astronomy, science, astrology, and how these subjects integrated with the religious philosophy of the time
The astrolabe was used both by astronomers and astrologers, and it was natural to apply a clockwork drive to the rotating plate to produce a working model of the solar system.
Simple clocks intended mainly for notification were installed in towers, and did not always require faces or hands
They would have announced the canonical hours or intervals between set times of prayer
Canonical hours varied in length as the times of sunrise and sunset shifted