Types of Clocks
A striking clock (also known as chiming clock) is a clock that sounds the hours audibly on a bell or gong. In 12-hour striking, used most commonly in striking clocks today, the clock strikes once at one a.m., twice at two a.m., continuing in this way up to twelve times at 12 noon, then starts again, striking once at one p.m., twice at two p.m., up to twelve times at 12 midnight.
The striking feature of clocks was originally more important than their clock faces; the earliest clocks struck the hours, but had no dials to enable the time to be read. The development of mechanical clocks in Europe was motivated by the need to ring bells upon the to call the community to prayer. The earliest known mechanical clocks were large striking clocks installed in towers in monasteries or public squares, so that their bells could be heard far away. Though an early striking clock in Syria was a 12-hour clock, many early clocks struck up to 24 strokes, particularly in Italy, where the 24-hour clock, keeping Italian hours, was widely used in the 14th and 15th centuries. As the modern 12-hour clock became more widespread, particularly in Great Britain and Northern Europe, 12-hour striking became more widespread and eventually became the standard. In addition to striking on the hour, many striking clocks play sequences of chimes on the quarter-hours. The most common sequence is Westminster Quarters.
Today the time-disseminating functions of clock striking are almost totally unnecessary, and striking clocks are kept for historical, traditional, and aesthetic reasons. Historic clock towers in towns, universities, and religious institutions worldwide still strike the hours, a famous example being Big Ben in London. Home striking clocks, such as mantel clocks, cuckoo clocks, and grandfather clocks are also common.
A typical striking clock will have two gear trains, because a striking clock must add a striking train that operates the mechanism that rings the bell in addition to the timekeeping train that measures the passage of time.
The most basic sort of striking clock simply sounds a bell once every hour. This sort of striking clock is called a passing strike clock. It is far simpler to create such a clock; all that must be done is to attach a cam to a shaft that rotates once an hour; the cam raises and then lets fall a hammer that strikes the bell. Originating before the mechanical clock itself, in water clocks, such clocks were the earliest striking clocks; they rang once for each canonical hour, and were used as reminders to summon monks or nuns to their prayers. This sort of striking is still found in some skeleton clocks. It does not require a separate gear train to arm and release the single stroke sounded.
The Tang Dynasty Chinese Buddhist monk and inventor Yi Xing (683–727) created a rotating celestial globe that was given motive power by hydraulics of a turning waterwheel (acting as a large escapement), in the tradition of Zhang Heng (78–139). This featured two wooden gear jacks on its horizon surface with a drum and a bell, the bell being struck automatically every hour and the drum being struck automatically every quarter hour. It is recorded that Confucian students in the year 730 were required to write an essay on this device in order to pass the Imperial examinations. The use of clock jacks to sound the hours were used in later clock towers of Song Dynasty China, such as those designed by Zhang Sixun and Su Song in the 10th and 11th centuries, respectively.