The hour clock is a time convention in which the 24 hours of the day are divided into two periods: a. The hour clock has been developed since the second millennium BC and reached its modern form in the 16th century.
The hour time convention is common in several English-speaking nations and former British colonies , as well as a few other countries. There is no widely accepted convention for how midday and midnight should be represented: in English-speaking countries, "12 p.
The natural day-and-night division of a calendar day forms the fundamental basis as to why each day is split into two cycles. Originally there were two cycles: one cycle which could be tracked by the position of the Sun day , followed by one cycle which could be tracked by the Moon and stars night.
This eventually evolved into the two hour periods which are used today, one called "a. Noon itself is rarely abbreviated today; but if it is, it is denoted "m. The hour clock can be traced back as far as Mesopotamia and ancient Egypt. The Romans also used a hour clock : daylight was divided into 12 equal hours thus hours having varying length throughout the year and the night was divided into four watches.
The first mechanical clocks in the 14th century, if they had dials at all, showed all 24 hours using the hour analog dial , influenced by astronomers' familiarity with the astrolabe and sundial and by their desire to model the Earth's apparent motion around the Sun. In Northern Europe these dials generally used the hour numbering scheme in Roman numerals but showed both a. This is known as the double-XII system and can be seen on many surviving clock faces, such as those at Wells and Exeter.
