


The hour: 14th century

Until the arrival of clockwork, in the 14th century AD, an hour is a variable concept. It is a practical division of the day into 12 segments (12 being the most convenient number for dividing into fractions, since it is divisible by 2, 3 and 4). For the same reason 60, divisble by 2, 3, 4 and 5, has been a larger framework of measurement ever since Babylonian times.
The traditional concept of the hour, as one twelfth of the time between dawn and dusk, is useful in terms of everyday timekeeping. Approximate appointments are easily made, at times which are easily sensed. Noon is always the sixth hour. Half way through the afternoon is the ninth hour  famous to Christians as the time of the death of Jesus on the Cross.




The trouble with the traditional hour is that it differs in length from day to day. And a daytime hour is different from one in the night (also divided into twelve equal hours). A clock cannot reflect this variation, but it can offer something more useful. It can provide every day something which occurs naturally only twice a year, at the spring and autumn equinox, when the 12 hours of day and the 12 hours of night are the same length.
In the 14th century, coinciding with the first practical clocks, the meaning of an hour gradually changes. It becomes a specific amount of time, one twentyfourth of a full solar cycle from dawn to dawn. And the day is now thought of as 24 hours, though it still features on clock faces as two twelves.




Even the first clocks can measure periods less than an hour, but soon striking the quarterhours seems insufficient. With the arrival of dials for the faces of clocks, in the 14th century, something like a minute is required. The Middle Ages, by a tortuous route from Babylon, inherit a scale of scientific measurement based on 60. In medieval Latin the unit of one sixtieth is pars minuta prima ('first very small part'), and a sixtieth of that is pars minute secunda ('second very small part'). Thus, on a principle 3000 years old, minutes and seconds find their way into time.
Minutes are mentioned from the 14th century, but clocks are not precise enough for anyone to bother about seconds until two centuries later.



