Stop the Clocks Trivia Quiz

This timekeeping device, the clepsydra, or water clock, measured time by the regulated flow of water. The example shown here is of an 'outflow clepsydra,' which is filled with water and allows water to drip out of a hole in the bottom at a steady rate. The other basic type of water clock is the (generally bowl-like) 'inflow clepsydra,' measuring time by how much water has accumulated. In both instances, the containers have graduated markings to mark the level of the water as it changes.

The example shown here is from Ancient Egypt, but clepsydras were also used in Babylon, in Ancient Greece (including gears and floats to enhance accuracy), in China and India (elaborate water clocks including automata and bells to signal time intervals), and during the Islamic Golden Age.

The drawing of the candle clock in this picture was made by Farruk ibn Abd al-Latif in his 14th century transcription of "The Book of Knowledge of Ingenious Mechanical Devices" (translated) by 12th century engineer and inventor Badi' al-Zaman ibn al-Razzaz al-Jazari.

Candle clocks were simple (yet ingenious) devices for measuring the passage of time through the controlled burning of a candle. Generally, a candle was marked with graduated intervals along its length, and as the wax melted, it showed the passage of time. Some candles were even embedded with weights or nails that would release and fall, making a noise like a rudimentary alarm clock.

And, of course, candle clocks could be used at night, when sundials were useless.

The clock shown in the picture is located at Salisbury Cathedral in England. It was constructed ca. 1386, and is believed to be the oldest working (mechanical) clock in the world.

The innovation of the verge and foliot escapement was developed ca. 1275, and was the first type of regulator in timekeeping devices. A technical description (per Wikipedia) describes its function as, "A verge, or vertical shaft, is forced to rotate by a weight-driven crown wheel, but is stopped from rotating freely by a foliot. The foliot, which cannot vibrate freely, swings back and forth, which allows a wheel to rotate one tooth at a time."

But these early mechanical timekeepers were not perfect, and would still need to be calibrated using a sundial.

The Egyptian shadow clock, also known as a shadow stick or gnomon, was a simple yet ingenious device used around 1500 BCE to measure time during the day. It consisted of a vertical stick or obelisk placed in the ground, with markings to track the movement of its shadow as the sun moved across the sky.

Egyptians divided their daylight up into 12 segments, and used the shadow clock to measure the passage of that time, observing the changing length and position of the shadow it cast. The concept was a precursor to the sundial, which was more precise and widespread in use in later civilizations.

Incense clocks originated in China in the 6th century CE, and were later adopted and refined in Japan. Unlike sundials or water clocks, incense clocks measured time by the burning of incense, which offered a unique blend of function and sensory experience. Specially-formulated incense sticks - designed to burn at a consistent rate - were marked or segmented to represent a fixed duration of time.

This basic function became more specialized in Japan, used in temples and homes to regulate meditation periods, tea ceremonies, and other rituals. Often the incense clocks were designed as artwork, adding a visual appeal to the aromatic properties, making for a more holistic experience when used.

An astronomical clock not only can display the time of day, but also various types of astronomical information, such as the positions of the sun, moon, and zodiac constellations, the lunar phases, and sometimes planetary positions, as well.

Pictured here, the Prague Astronomical Clock (or Prazský orloj) is one of the oldest such devices that is still original and operating. It was installed in 1410 by Mikulás of Kadaň (a clockmaker) and Jan Sindel (professor of astronomy at Charles University), and has survived wars, fires, and restorations over the centuries.

This specific example of an Astronomical Clock includes an astronomical dial showing the positions of the sun and moon, old Czech time, central European time, and Babylonian time, and also includes a zodiac ring and background astrolabe. It also has a calendar dial with medallions for each month and the patron saints' days.

Pendulums improved on the design of the verge and foliot escapement, and were first developed for timekeeping by Christiaan Huygens in 1656 (and patented in 1657). Inspired by Leonardo da Vinci's studies on pendulums, Huygens' work managed to improve accuracy from a variance of 15 minutes in a day to just 15 seconds.

The hourglass, also called the sandglass or sand timer, has likely been around since the 8th century CE, although documentary evidence only appears around the 14th century. Believed to have developed from the clepsydra, this simple yet functional timekeeping device is typically constructed of two glass bulbs connected by a narrow neck, which allows sand to flow from one bulb to the other at a measured rate.

The duration it measures depends on the amount and size of the sand, the width of the neck, and potential environmental factors such as humidity.

Constructed in 1724, the Brihat Samrat Yantra ("Great King of Instruments") was one of five very large sundials distributed around India Maharaja Jai Singh II, scholar and ruler of Jaipur.

The massive triangular gnomon is aligned with the Earth's axis and is flanked by two quadrants with finely-graded scales that let observers measure the time of day with precision (accurate to within two seconds).

In addition to basic timekeeping, the Samrat Yantra was used to track the movements of celestial objects, to predict eclipses, and refine the calendar system.

An astrolabe is essentially a portable version of an astronomical clock; a two-dimensional model of the celestial sphere. Its main functions include determining time (based on the position of the Sun or stars), finding latitude (by measuring the altitude of celestial objects), solving problems in spherical astronomy (such as predicting sunrise and sunset), and navigating at sea.

The primary components of an astrolabe are: the mater (base plate, engraved with coordinate grids), the rete (a rotating star map with pointers for prominent stars), the alidade (a sighting rule used to measure angles), and climates plates (interchangeable disks for different latitudes).

Astrolabes have been around since the times of Ancient Greece, likely developed by Hipparchus or Ptolemy (ca. 150 BCE) who described the key principles behind the astrolabe in their writings.

The atomic clock is the most accurate timekeeper that has been invented. The idea for using atoms for timekeeping originated with James Clerk Maxwell and Lord Kelvin in the 1870s. In 1945, it was physicist Isidor Isaac Rabi who came up with the idea of atomic beam magnetic resonance to build a clock.

From there it was just a matter of time (pun intended), and the first functioning atomic clock was constructed in 1949 by the National Bureau of Standards using ammonia molecules to measure microwave resonance frequencies. In 1952 the first cesium-based atomic clock was built, and this has become the standard for modern atomic timekeeping.

The maritime chronometer was developed during the age of exploration as a response to solving the Longitude Problem. Latitude could be determined easily enough while at sea by measuring the angle of the Sun or stars above the horizon, but longitude required knowing the exact time at a reference location (such as Greenwich) and comparing it to local time.

In 1717 the British government offered a prize of 20,000 pounds for a method to determine longitude at sea within half a degree, and the challenge was met by John Harrison. His first model (H1) was developed in 1735, but it took until 1759 and model H4 to build a chronometer that was accurate enough to meet the standards of the prize.

Using the maritime chronometer and a reference to Greenwich Mean Time (GMT), navigators measured local noon (the Sun directly overhead) and compared it to GMT. And knowing that the Earth rotates 15 degrees every hour, each hour of time difference equaled 15 degrees of longitude distance.