The Measurement of Time

~~ Paul V. Hartman ~~


       The first people to keep time noted that certain natural events repeated themselves. Such events became the probable basis for measuring other things which were not cyclic. The most obvious cyclical change apparent to early man was the daily appearance of the sun. Whatever name was given for this phenomenon then, it is now called a "day". A second observation was that it took about 30 of these "days" for the moon to cycle through a complete set of its shape "changes". To this was given a name which meant "month".

The division of the day into hours, minutes, and seconds, is attributed to the Babylonians - and particularly the 11th Dynasty thereof, those we refer to as the "Chaldeans" - who were evidently intrigued by multiples of twelve.(1)   The Babylonians divided the portion of the day which was lit by the sun into 12 parts, and the dark interval into 12 more, yielding 24 divisions which we now call "hours." Babylonian mathematicians divided a complete circle into 360 divisions and each of these divisions into 60 parts. Babylonian astronomers chose the same number 60 to subdivide each of the 24 divisions of a day, each of which was then also divisible into 60 parts. Of course, they had no mechanical way to measure time as precisely as seconds, nor the passage of long periods accurately in hours, but they could make calculations in that regard. Time and astronomy were wedded in the same system.

We suspect that the steady shortening of shadows leading up to that point in the day when the sun was directly overhead, followed by the shadows lengthening again prior to dark, was an early observation which could be captured in a handy fashion by some sort of sundial, a stick in the sand being the simplest example. Sundials resembling the modern garden form can be dated in Egypt to 2400 BC and were probably older.

The next step was to move beyond the need for the sun being present to measure time, by burning a candle of a measured size to approximate the passage of time. The larger leap was to compare either of these techniques with the amount of water that would fall in a steady stream through a set orifice, at which point early man was on the way to measuring time "mechanically". Since dripping water can turn a small wheel, the Greeks (c 340 BC) employed water clocks (called klepsydra) which rang bells and moved mechanical birds. The Romans set water clocks near public sundials for use on cloudy days. Such clocks, using sand, which did not evaporate, would eventually replace those using water. When the glassblowing art reached a sufficient level, it was then possible to make a self-contained sand clock which was portable, surviving to this day as the egg timer.

The early Romans had three "hours" - sunrise, noon, and sunset. By about 1 AD, they were subdividing daylight into 5 "hours". In the seventh century, the Catholic Church settled on 7 hours of daylight, named matins (morning), lauds (praise), prime, tierce, sext, nones, vespers (evening), and complin. (The nights were divided into "watches", during which guards relieved other guards.) Since summer days were longer than winter days, summer "hours" were longer than winter "hours". The New Testament records a period in which both hours and watches were used side by side.

Ticking off time by having a wheel or gear rotate under the gravity of an attached falling weight appeared in the late 13th century. Such a mechanical device could be arranged to ring a bell each time a pin on a wheel passed a mark representing a 24th part of a day. By the beginning of the 16th Century, mechanical clocks based on falling weights appeared as a public service on churches and official buildings, divided by a large "hand" into 12 "hours". They were not accurate, as weight accelerates as it falls, and clocks "sped up" as the weight got closer to the ground. They could be reset on any day in which the sun revealed its "noon" position directly overhead, but real progress would await, first, the use of a "brake", and later, the invention of an escapement mechanism. The mainspring also appeared in the 16th century and pocket clocks would follow.

In the 17th Century Galileo invented a clock based on the movement of a pendulum. In the 18th Century a man named John Harrison solved an annoying nautical problem (the need to determine longitude at sea, which depends on accurate time) with his marine chronometer.

The lunar cycle of about 28-29 days, and the solar cycle of 365 days, have no natural relationship, and the selection of how many days there should be in a "week" is purely arbitrary. The 7 day week of the Hebrews was based on a preference for that number and probably originated with the earlier Sumerians, who based it on the 7 heavenly bodies then known, and who are also credited with originating history. ("History begins at Sumer") The Incas had an 8 day week as did the Romans, who only modified it to 7 when the Roman world became Christianized with Constantine. The earlier Greeks had no week at all, just a 30 day month. At its origin in 1917, the Soviet Union adopted a 5 day week.

Our current method of dealing with time - world wide - is a rich amalgam of techniques adopted by a variety of ancient cultures. We have a 24 hour day from the Chaldeans, and a 7 day week from the Sumerians and Hebrews, but the days are named for a mix of Roman and Germanic gods, the names themselves written with an alphabet invented by the Phoenicians. We use a calendar which originated with the Egyptians, modified by the Romans (in use for 15 centuries), modified again by a Catholic Pope in 1582, still in use 4½ centuries later. Thus there is a lot of history which goes into the (very hackneyed) phrase when we say to another: "Have a nice day".

(1)   This was a sexagesimal system with a base-60 notation, and employed tables and reciprocals to reduce the need for long division and multiplication. The system did not have a zero! Yet it was more manageable than the Egyptian system by which addition was possible but multiplication difficult. Even the Romans, who appeared much later (to rule the world), were burdened with Roman numerals which could be added with difficulty and multiplied not at all! Read more about the sexagesimal system Here.



--= The Hartman Web Site © , 1995 - 2006 All rights reserved. =--