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 The more sophisticated astronomical clocks would have had moving dials or hands, and would have shown the time in various time systems, including Italian hours, canonical hours, and time as measured by astronomers at the time Both styles of clock started acquiring extravagant features such as automata. In 1283, a large clock was installed at Dunstable Priory; its location above the rood screen suggests that it was not a water clock In 1292, Canterbury Cathedral installed a 'great horloge' Over the next 30 years there are brief mentions of clocks at a number of ecclesiastical institutions in England, Italy, and France In 1322, a new clock was installed in Norwich, an expensive replacement for an earlier clock installed in 1273 This had a large (2 metre) astronomical dial with automata and bells The costs of the installation included the full-time employment of two clockkeepers for two years. Early astronomical clocks Richard of Wallingford pointing to a clock, his gift to St Albans Abbey Besides the Chinese astronomical clock of Su Song in 1088 mentioned above, in Europe there were the clocks constructed by Richard of Wallingford in St Albans by 1336, and by Giovanni de Dondi in Padua from 1348 to 1364 They no longer exist, but detailed descriptions of their design and construction survive, and modern reproductions have been made They illustrate how quickly the theory of the mechanical clock had been translated into practical constructions, and also that one of the many impulses to their development had been the desire of astronomers to investigate celestial phenomena. Wallingford's clock had a large astrolabe-type dial, showing the sun, the moon's age, phase, and node, a star map, and possibly the planets
