Grandfather Clocks, Wall Clocks, Cuckoo Clocks & More!

Clocks have been around for some 5000-6000 years. Even prior to that time man observed the regularity of the day with the rise of the sun and eventual night fall.

The word clock is ultimately derived from the Celtic words clagan and clocca meaning "bell" implying a striking mechanism of some type while the absence of such a mechanism has historically been associated with what is known as the timepiece.

Clocks like many things evolved over time. The evolution produced five known categories of clocks. These were the sundial, the water clock, the division of the day as a measurement, the pendulum clock and finally the quartz clock.

A sundial is used to measure time according to the suns position. This is one of the oldest types of clocks developed in an effort to measure time. The sun clock was developed approximately 5500 years ago. In this clock the sun simply casts a shadow across what is known as the style, which must be set to true north to provide a good estimate of the time. There are other important parameters in the setup as well.

Some 4000 years ago the Eygptians and Babylonians began to divide the day into equal increments. First was the notion of 12 parts by day and 12 parts by night. Part of the basis was couched in the notion that the cultures observed that there were 12 moon cycles in a year. The second evolution of these observations rested on dividing each of the 24 parts (hours) by 60. The number 60 is interesting and is part of the sexagesimal system, which is based on the number 60. The basis for the number 60 includes a number of interesting mathematical observations and can be explored further by researching the sexageismal system.

Utilizing this system allowed the Babylonians to divide each of the 24 parts into minutes and the minutes by 60 or seconds. This had the effect of measuring time at a higher resolution.

As time progressed evolution of the clock finally manifested itself in the form of a device. One of the first was the water clock. The water clock or clepsydra as it is known was developed by the Eygptians approximately 3400 years ago. Such clocks were also known by the Babylonians during this time period. In this case the time is measured by the regulated flow of liquid into or out from a container. Many of these types of clocks simply allowed water to drip through a small hole at a near constant rate. Later, more sophisticated designs included regulating water flow and pressure and connecting various mechanisms that rang bells or gongs.

The water clock offered two advantages over sun dials; (1) they were more accurate and (2) not only was time measured during the day but now an assessment of time could be made at night.

The pendulum clock clock makes use of a pendulum, a swinging weight, as the key feature in timekeeping. Credit for the invention in 1656 is given to Christiaan Huygens. Up until the 1930s, the pendulum clock was the world's most accurate timekeeper. Actually Galileo first had the idea of using pendulum for keeping time as early as 1637 and his son actually begin to build one but neither lived to finish it. The pendulum clock offered the world accuracy to within about 15 seconds versus 15 minutes. As a result it became very popular. Utilizing a pendulum to keep time was essentially making use of the pendulum as an harmonic oscillator. After the invention of the pendulum clock it was discovered that small swings (not large) increased the accuracy of the clock. This was attributable to the higher variability in what is known as the period of the clock. Smaller swings were associated with less period variability.

A quartz clock is a clock that makes use of an electronic oscillator, which is regulated by a quartz crystal. Quartz is essentially silicon dioxide. It was discovered that when an electronic voltage is applied to quartz a frequency is generated via oscillation, which, as it turns out, is extremely consistent. There are a number of other factors that affect the oscillation such as the electrode placement and shape and size of the crystal.

The technology provided for tying the oscillation to digital logic counts, which then was conviently linked to digital time display. Another important advantage crystal affords is that the frequency is virtually unchanged by temperature. The first quartz crystal oscillator was built by Walter G. Cady in 1921. Consequently, since about 1970 this form of timekeeping has become the dominant as the accuracy far exceeds the pendulum clock.

Lord Kelvin is given credit for first suggesting the use of measuring time via atomic vibration back in 1879. The first commercially available atomic clocks were built in the late 1950’s. Although earlier atomic clocks were based on magnetic resonsance and, in some cases, radioactive compounds, the modern atomic clock makes use of an atomic resonance frequency standard as the basis for keeping time. These clocks represent the most accurate known and essentially are used as the primary time standards.

Atomic clocks do not make use of radioactivity but rather microwave signals and associated changes at the atomic level due to changes in energy levels. The most accurate atomic clocks are based on absorption spectroscopy. Atomic clocks have accuracies up to 10-9 seconds per day or 1/billionth of a second. Pictured here is NIST-F1, the nation's primary time and frequency standard clock, a cesium fountain based atomic clock located in Boulder, Colorado. This clock represents the official world time and has an uncertainty of about 5 x 10-16, which means it would neither gain nor lose a second in more than 60 million years!