While we all know that a clock refers to any device used to measure and display time, the word clock itself means bells in Celtic, and is derived from the words clagan and clocca. Clocks, for that matter, can be considered to be one of the oldest inventions of man.
Today, all clocks and watches can divided into two broad categories―analog and digital―based on the way time is displayed. To better understand how various types of clocks or timekeeping devices are classified, let's take a look at clocks given in the paragraphs that follow.
Call it a blast from the past, these devices indicate the position of the Sun in the sky. The sundial uses a gnomon―shadow-casting object or arm―that can be anything from a thin rod to a sharp-tipped object to determine the position of the Sun at the particular time of day. It indicates the time by casting a shadow on a flat surface with markings that usually corresponds to the hours of the day. Sundials can either be horizontal or vertical; however, their limitation is fairly obvious, they cannot measure time after sunset, or when the conditions are overcast.
Clepsydra or water clocks are possibly, the oldest time-measuring instruments that are known to have existed in Babylon and Egypt around the 16th century BCE. Time was measured by the regulated flow of liquid from one vessel into another, where the amount was then measured. Modern water clocks keep time by a calibrated pendulum that is powered by a water stream piped in from the clock's reservoir. Royal Gorge Park at Colorado, Woodgrove Center in Nanaimo, and Abbotsford International Airport in British Columbia are among a select few places where modern design water clocks are still in use.
The most common image that comes across your mind when you hear the word clock is that of the analog clock. Popular the world over, and available in all shapes and sizes, an analog clock indicates time using three arrows or hands. The clock has a fixed dial that has calibrations or markings along its circumference, indicating 12 hours, these are further calibrated into 60 markings, each indicating a minute. All three hands or arrows rotate across the dial to indicate the passing hours and minutes. Traditionally, analog clocks worked on the spring and gear mechanism, and the spring had to be wound using a key. Today, the advent of quartz and button cells has made winding a clock almost obsolete, barring certain antiques and collectibles. At certain defense establishments you may find a 24-hour analog clock that is used to tell military time.
Another popular display of time is via the digital clock which employs LCD, LED, or VFD to display time. These clocks indicate time in hours, minutes, and seconds. Digital clocks can indicate either a 12-hour format or the 24-hour format, while some indicate the date and day of the week too. These clocks can be powered by a quartz crystal or AC power. The only downside of a digital clock is that it resets every time the batteries die down, or if you have a power failure.
Mechanical or Pendulum Clocks
Mechanical clocks are powered by a mainspring that unwinds and moves the gears holding the hands of the clock. An escapement mechanism enables precise gear movement and provides oscillation motion to the pendulum. Each swing of the escapement triggers the movement of gears and subsequently power the gear train that drives the hands on the dial. This movement also creates the ticking sound common to pendulum watches. Certain pendulum clocks need timely winding of the mainspring once it unwinds completely.
Radio clocks display the time signals encoded and transmitted from radio stations. In turn, the encoded time signals from radio stations derive their time from atomic clocks that measure time. The clock is simply a radio receiver with a digital display that transmits the information it receives through long and short waves. The radio clock adjusts the time on the display according to the information sent by its host. Radio clocks can also keep time with a quartz crystal, and are periodically synchronized to either standard time radio stations or satellite navigation signals.
Atomic clocks measure time by using electronic transition frequency placed in the ultraviolet region of the electromagnetic spectrum of atoms as a frequency standard. These are known to be the most accurate clocks and are widely used to synchronize wave frequency of television broadcasts and in global navigation satellite systems. The accuracy of the atomic clock depends on two factors: First, temperature of the atoms, and second, the frequency and intrinsic width of the transition.
A quartz clock uses a quartz crystal to generate a oscillating electronic signal with very precise frequency to measure time. The quartz crystal resonates at a constant 32,768 Hz, making it one of the most accurate and efficient clocks used today. The best part about these watches is that the resonator crystal does not change frequencies with changes in temperature, making it a stable choice for indicating time in extreme temperatures.
Cuckoo clocks use weight and pendulums to measure time. The only factor that sets them apart is the way they chime or tell time every hour. These clocks have a little door on their face that opens up to reveal a tiny mechanical bird that calls the hour―chirps according to the time, or in modern clocks plays a melody. Known for their intricate designs, these clocks are quite popular and are considered an owner's pride.
Shaped like a lantern, these clocks were generally hung on walls. These clocks worked with weights and balance wheels, just like all other mechanical clocks of the time. Made entirely from copper alloy― mainly brass―these clocks were also called Cromwellian, bedpost or birdcage clocks. Though obsolete, they make perfect wall clocks for those interested in antiques.
Just like the name suggests, mantel clocks were used to adorn the top of the fireplace or mantel. Known as shelf clocks, the working of these clocks is triggered by a wound mainspring. Weight-driven mantel clocks could be adjusted through a hole in the clock face which eliminated the need to open the case to set it into motion. These are most sought after clocks by antiquarians and museums.
Grandfather and Grandmother Clocks
The name gives it away, known for its characteristic long case, the grandfather, grandmother, and granddaughter clocks are encased in long cases. These clocks came with either one of the two mechanisms―eight-day mechanism and one-day mechanism. The only difference being, the one day mechanism clock needed to be wound on a daily basis, while the eight-day clock once every eight days. The striking difference between grandfather, grandmother, and granddaughter clocks is their height. Anything above 6 feet is a grandfather clock, while anything below 5 feet is a granddaughter clock, and the grandmother lying in between.
This clock is specifically designed for people with visual impairment. The primary difference between a tactile clock and a regular analog clock is that the hands and tactile markings on the dial are slightly raised so that time can be read by touching the hands and markings.
A speaking clock, also known as an auditory clock, is a device that uses a prerecorded human voice to read out the time. To say the least, these clocks are beneficial for those with affected vision as it reads out the time to the individual.
With the passage of time, clocks have conveniently made the change from being pure functional devices to aesthetic pieces of home decor. Point in case, where a digital or electric clock would look appropriate for a sleek and modern home, while an analog or a mechanical grandfather clock would really complement a classic, old-world library with oak furniture. Armed with this knowledge about the various clocks, go ahead, choose your timekeeper to suit your interior.