Primitive methods of measuring time Prehistoric man, by simple observation of the stars, changes in the seasons, day and night began to come up with very primitive methods of measuring time. This was necessary for planning nomadic activity, farming, sacred feasts, etc. The earliest time measurement devices before clocks and watches were the sundial, hourglass and water clock.

1. History of time and its Facts

3. Primitive methods of measuring time The forerunners to the sundial were poles and sticks as well as larger objects such as pyramids and other tall structures. Later the more formal sundial was invented. It is generally a round disk marked with the hours like a clock. It has an upright structure that casts a shadow on the disk - this is how time is measured with the sundial.

4. Sundials Egyptians measured the time of day by using Sundials. Sundials rely on the sun to tell time. These early timekeepers discovered that hours are shorter in the winter and longer in the summer. Sundials can only be used during the day to tell time. After a while, the Egyptians and other ancient societies realized that the Sun rose and set in different places in the Summer and winter. In fact, the sun never took the same course on any one day throughout the year! They tried everything, until they Realized that if they would just put the post of the sundial in at a special angle, it would work all year

5. Water Clocks A water clock or clepsydra Greek κλέπτειν kleptein ,'to steal'; ὕδωρ hudor , 'water‘” is anytimepiece in which time is measured by the regulated flow of liquid into ‘inflow type’ or out from ‘outflow type’ a vessel where the amount is then measured. Made up of two containers, water drips from the higher container to the lower container. The point at which the water is collected raises a floating device which triggers the pointer to mark the hour. These clocks worked better than the sundial because they were able to tell time at night. In later years these clocks were adopted by the American Indians.

6. Candles A candle clock is a thin candle with consistently spaced markings (usually with numbers), that when burned, indicate the passage of periods of time. While no longer used today, candle clocks provided an effective way to tell time indoors, at night, or on a cloudy day.

7. Incense Clocks In addition to water, mechanical, and candle clocks, incense clocks were used in the Far East, and were fashioned in several different forms. An incense stick clock was an incense stick with calibrations, most were elaborate, sometimes having threads, with weights attached, at even intervals. The weights would drop onto a platter or gong below, signifying that a certain amount of time had elapsed. Sticks of incense with different scents were also used, so that the hours were marked by a change in fragrance.

8. Hourglass The hourglass is sometimes referred to as a sand clock or a sandglass. Like other timepieces, it needs to be carefully calibrated. The hourglass maker must test the instrument and fine tune it to measure the correct length of time. There are many factors that contribute to the ability of an hourglass to accurately measure time. The type and quality of sand is key. It must have a rate of flow that does not fluctuate. Sand that is too coarse will wear away the glass, eventually making the neck too large. Most important is the ratio of the neck (the hole, or tube) width to the diameter of the sand particles.

9. Bells King Charles V of France decided that all Paris church bells must ring at the same time as the Royal Palace. This stopped the ringing of bells during prayer time. The name “Clock” originally meant “Bell.”

10. Astronomical Clocks The term is used to refer to any clock that shows, in addition to the time of day, astronomical information. This could include the location of the sun and moon in the sky, the age and phase of the moon, the position of the sun on the ecliptic and the current zodiac sign, the sidereal time, and other astronomical data such as the moon's nodes (for indicating eclipses) or a rotating star map

12. Modern Inventions

13. Mechanical Clocks The difficulty in inventing a mechanical clock was to figure out a way in which a wheel no bigger than a room could turn at the same speed as the Earth, but still be turning more or less continuously. If this could be accomplished, then the wheel became a mini-Earth and could tell the time. For, after all, the time is nothing more nor less than how far the Earth has turned today.

14. Pendulum clock Galileo made an amazing contribution to the world of time, simply by not paying attention in church. The year was 1581 and Galileo was 17. He was standing in the Cathedral of Pisa watching the huge chandelier swinging back and forth from the ceiling of the cathedral. Galileo noticed that no matter how short or long the arc of the chandelier was, it took exactly the same amount of time to complete a full swing. As the pendulum swings left to right, a wheel with teeth turns the hour and minute hands. The second hand on the clock was developed at this time. This clock was more accurate than any previous clock invented.

15. Wristwatches n 1904, Alberto Santos-Dumont, an early aviator, asked his friend, a French watchmaker called Louis Cartier, to design a watch that could be useful during his flights. The wristwatch had already been invented by Patek Philippe, in 1868, but only as a "lady’s bracelet watch“. As pocket watches were unsuitable, Louis Cartier created the Santos wristwatch, the first man's wristwatch and the first designed for practical use. Wristwatches gained in popularity during World War I, when officers found them to be more convenient than pocket watches in battle.

16. Marine Chronometers Marine chronometers are clocks used at sea as time standards, to determine longitude bycelestial navigation. Marine chronometers keep the time of a fixed location—usually Greenwich Mean Time—allowing seafarers to determine longitude by comparing the local high noon to the clock. According to COSC, a chronometer is a high-precision watch, capable of displaying the seconds and housing a movement that has been tested over several days, in different positions, and at different temperatures, by an official, neutral body.

17. Atomic clocks Atomic clocks are the most accurate timekeeping devices known to date. Accurate to within a few seconds over many thousands of years, they are used to calibrate other clocks and timekeeping instruments. Atomic clocks have employed other elements, such as hydrogen and rubidium vapor, offering greater stability—in the case of hydrogen clocks—and smaller size, lower power consumption, and thus lower cost (in the case of rubidium clocks).

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