Measurement of Time

Have you ever thought why are there sixty minutes in an hour and sixty seconds in a minute? Why is there is 12 hour clock and a 24 hour clock?


The measurement of time was started by the ancient Egyptians who divided it between day time, measured with a sundial during the day and at night time by looking at the moon and stars and measured by a water clock. They were the first to use a 12 hour clock.

At night the Egyptian used an astronomical system of decans. 

The decans; are 36 groups of stars (small constellations) which rise consecutively on the horizon throughout each earth rotation. The rising of each marked the beginning of a new decanal "hour" of the night.


Later the Babylonians (in about 300-100 BC) performed astronomical calculation in the sexagesimal (base-60) system. This was extremely convenient for simplifying time division, since 60 is divisible by 2, 3, 4, 5, 6, and 10. What we call a minute derives from the first fractional sexagesimal place; the second fractional place is the origin of the second.

The Romans were not so clever besides having a numerical system, using V and X, that made mathematical calculation almost impossible, they divided daylight into 12 hours. This meant one hour in winter was shorter than an hour in the summer.

We have wisely adopted the Arabic numerals and made hours of equal length.

In Great Britain at first midday was measured by a sundial and the  time shown on the town clock regulated with a pendulum and showing the time on a 12 hour dial. Personal watches were not available. The more well-to-do would have a grandfather clock which had a pendulum of such a length that it swung once a second.. Smaller grandmother clocks were made with smaller pendulums.

In the 1700s navigation at sea was hampered by the difficulty in determining longitude, because the exact time could not be determined on board ship. Many shipwrecks occurred in particular one off the Isles of Scilly in 1707. A reward of £20,000 (equivalent to £2.58 million in 2016) was offered by Parliament for a method of correctly calculate longitude. This problem was tackled by John Harrison, a self-educated English clockmakerHarrison built his first  grandfather clock in 1713, at the age of 20, entirely of wood. In 1778 he invented the marine chronometer which used a spring balance instead of the pendulum which of course could not be use on an unsteady boat. There were already watches using a spring balance but they did not keep good time. One problem was the expansion and contraction of the components. This was also a problem with pendulums. Harrison had invented the gridiron pendulum, consisting of alternating brass and iron rods assembled so that the thermal expansions and contractions essentially cancel each other out . Over many years and after many attempts he produced the 'H4'

A very accurate sea watch. In all he received  £23,065 awarded in stages overall over many years.

Nowadays time at sea is kept accurate by radio and a quartz clock. A quartz clock is a clock that uses an electronic oscillator   that is regulated by a quartz  crystal to keep time. This crystal oscillator creates a signal with very precise frequency, so that quartz clocks are at least an order of magnitude more accurate than mechanical clocks The first quartz clock was built in 1927 by Warren Marrison and J.W. Horton at Bell Telephone Laboratories. Since the 1980s when the advent of solid state digital electronics allowed them to be made compact and inexpensive, quartz timekeepers have become the world's most widely used timekeeping technology, used in most clocks and watches, as well as computers and other appliances that keep time.

Earlier in Great Britain the 12 hour clock was used and recorded by sundial locally for each town and this was satisfactory until the advent of train travel. This was much faster than horse drawn coaches over rough roads, and so the fact that midday in the West of the Country was after midday in Greenwich became apparent Every 1° longitude difference means 4 minutes difference in time. So Greenwich meantime, which had been used at sea for many years, became the norm throughout the Country.

All the lines of longitude meet at the north and south poles. So the time here is any time you wish plus you have the choice of two possible days as the international date line also is here.

The 24 hour clock was only brought into use in about the 1900s.

The 12 hour clock is still commonly used with a.m. (ante meridiem) morning and p.m. ( post meridiem) afternoon. There can be some confusion texting with a French person where am may be interpreted as 'après midi' afternoon.

The 24 hour clock is used for travelling times to be perfectly clear.

Because the sun appears in the east of the globe first, countries, to the east have their local time set before Greenwich mean time (GMT) This generally uses a variation in whole hours. However India has a difference of 5 ½ hours from GMT and it means that a watch showing British time can be turned upside down to show Indian time.

Summertime or daylight saving time is observed by moving the clocks one hour back in the autumn and one hour forward in the spring (fall back & spring forward).

The clocks are put forward one hour in advance of GMT at 1a.m. on the last Sunday of March. Clocks are put back to GMT at 1 a.m. on the last Sunday in October. It means that there is an extra hour of daylight in the evenings in the summer months and of course one hour less of daylight in the mornings. As the sun rises early in summer mornings this is of no disadvantage.

Neat Numbers

I put this item in as it is so difficult to estimate the passing of time. Time seems to go at various speeds according to what we are doing at the time.  Estimating time can be practiced using neat numbers. 

Neat numbers are observed if you have a digital clock. This is often a radio alarm alongside your bed.

Examples of neat numbers are:-

2.10,  2.22.  2.34,  2.46, and 2.58. It will be observed that each differs from the next by 12. (also a neat number) There are many more neat numbers starting with 3,4 & 5. e.g. 321 etc.

During the night if you suffer from insomnia you can look out for neat numbers and see if you can open your eyes to coincide with a neat number being displayed. This is not easy as estimating how much time has passed is difficult.

Incidentally insomnia should not be considered an annoyance but a chance to spend more time in bed. When asleep time passes very quickly and we all enjoy a Sunday lie in, don't we.