When, and why, did it become necessary for mankind to measure the passage of time in a resolution finer than days? And when did time become standardized?
The why of this question was quickly answered by my friend, Frank Coakley, who suggests that humankind found it necessary to measure time in increasingly small intervals when teenagers started dating at night. Sounded good to me, but he had no citation, so I hadda do the research anyway.
The day is the briefest division of time with a basis in the real world: It is the period consisting of one (1) daylight and one (1) night cycle, caused by the rotation of a planet. We measure it midnight to midnight now, but it has been variously been calculated throughout history as noon to noon, dawn to dawn and sunset to sunset. It has two real world companions, the solar year and the lunar month. All other time periods are indexes; that is, arbitrary parsings of these three relatively concrete intervals. There has been little standardization throughout history of any of the time indexes, probably because they are all arbitrary.
Our most distant ancestors (who gave a hoot) probably didnít care about anything besides days, and the passage of seasons. The next level of awareness was of the cycle of the moon: the month. That period was short enough for primitives to recognize, is very close to the average menstrual period of women and closely matches the cyclic behavior in some marine mammals. The month seemed to possess great significance to our forebears, and became the governing period for many religious observances. Early man probably didnít give an edible root about the year; he was too busy trying to survive the day.
Weeks came about when there was sufficient commerce to require an interval longer than the day, but shorter than the month. The first such demarcation was the interval between market days, four to ten days, depending on where you lived. The Roman internundium was the eight day period between market days. The Babylonians were taken with the days that were multiples of seven; seven represented the number of planets known to them, and was a sacred digit to this civilization. The four phases of the lunation occur approximately seven days apart as well. This became our week.
Now to Jamieís actual question: The hour was the first index of time shorter than the day, and itís probable that it was invented before it was really needed.
In about 3500 BC, the gnomon was invented. It was basically a stick poked in the ground, and the length of the shadow that it cast indicated the time of day. The more accurate sundial was in existence by the 8th century BC. The Egyptian shadow clock still preserved from this period had six time divisions on its base. By 300 BC, the Babylonians had begun to use a hemicycle, which generated a shadow in a hemispherical space which traversed a circular arc divided into twelve sections.
A significant fact about all of these devices is that they parsed an interval, daytime, which varied during the course of the seasons. Thus, the hours they measured varied in length. Consequently, they were known as temporary hours, and did not represent the standardization of anything.
Now, the sundial was of little use at night. The clepsydra, or water clock, measured the passage of time at night, by the gradual flow of water. It may have been an invention of the Chaldeans of ancient Babylonia. Yes, them again. Clepsydras from the 14th century BC still exist. They are Egyptian.
In the article I read on water clocks, I noted the first mention of a reason for measuring time in such relatively small increments; clepsydras were used to time the speeches of orators.
Such devices may have first been used to aid in early scientific queries. We know that, much later, Galileo used a mercury clepsydra to time his experimental falling bodies. Earlier civilizations (Arabic, Greek, Babylonian, et al.) would have needed duration timers for their inquiries into the phenomenological world. These devices didnít need to measure the same intervals from place to place. I suspect that navigation at sea represented the first good reason for needing a global standard of time. In the 16th century, astronomers evolved the principle of determining longitude by comparing the local time with the reading of a clock that reliably kept the time of a known meridian. Such a device was not invented until 1761, almost fifty years after the British Parliament offered a £20,000 reward for its creation.
I think that answers Jamie pretty well, but Iím not satisfied, nor was humankind. Next month Iíll touch on shorter intervals and the modern usages and measurement of time. Thatís a MSN month, of course. Your mileage may vary.