Introduction
Human beings have been fascinated with time for tens of thousands of years. Early Homo sapiens used time to know when to hunt, rest, cultivate, etc. For measuring time accurately, Neolithic humans began to construct timekeeping devices, which later came to be known as clocks. These clocks added punctuality to the human mainframe and accelerated efficiency to a great extent. In this blog, we discuss nine such clock models that revolutionized the field of Horology (the field of measuring time and making timekeeping devices). We discuss their construction, working, and their impact on timekeeping. So, let’s explore the evolution of clockmaking technology through the sands of time.
Chapter 1: Sundial (~3500 BCE – 1600 CE)
Sundials are the earliest known clocks or timekeeping devices, created by human beings. They consisted mainly of a platform with indicator markings and a rod-shaped figure above it, also known as a gnomon. During the day, the gnomon cast a shadow over the platform, whose length and angle were measured and calculated to find the exact hour. The device depended on human observation and calculation, and only worked when sunlight was available. Sundials were soon replaced by more efficient clocks in the future, especially the mechanical clock. They are still on display in various regions for decorative and educational purposes.
Chapter 2: Water Clock / Clepsydra (~1500 BCE – 1600 CE)
Water clocks (or Clepsydras) were one of the earliest known clocks made by man, which were independent of any external cause, like sunlight. They were famous in ancient Egypt, Greece, and China. They were built with various designs, especially the Chinese and Arabs devised many complicated mechanisms. In simple terms, the device consisted of two containers connected through a simple pipe or a hole. Water was poured into one of the containers and allowed to drip into the other at a controlled and measured rate. The empty container had markings that could indicate the time passed based on the volume of water filled. In some models, markings were instead on the container filled with water, and time was calculated on the basis of the decrease in water levels of the container. In both models, the water clocks proved superior to sundials and were used mostly at night. Their use declined after the invention of the mechanical clock during the 15th-16th centuries.
Chapter 3: Candle / Incense Clock / Hour Glass (~500 – 1800 CE)
Around the middle of the first millennium CE, a new type of mechanism was created to make timekeeping portable, so it could be carried from one place to another. Thus, the candle clock and the hourglass were invented. The candle clock was nothing but a candle with markings on it that indicated the time elapsed as the candle burned over the course of time. Hourglasses, on the other hand, were an improvisation on the water clocks, where sand and glass bulbs replaced water and containers. The amount of sand passed from one bulb to another indicated the time elapsed. After the entire sand had passed to the second bulb, the clock could be easily reset by just switching the second bulb on top, so that sand could then pass to the first bulb, and the clock worked in the opposite direction. Hourglasses were mainly used in long voyages, while the candle clock was mainly used for domestic and ceremonial purposes. Their use declined around the 17th-18th century due to the invention of more advanced clocks.
Chapter 4: Mechanical Clock (~1300 – 1800 CE)
Mechanical Clocks were the earliest form of properly engineered clocks. They were much more accurate compared to their predecessors and slowly led to their decline in usage. A typical mechanical clock consists of 5 parts: a power source, a gear train, an escapement, a regulator, and an indicator. In the earliest mechanical clocks, a falling weight was used as the power source. The falling weight interacting with gravity created a steady pull that drove the gear train. A gear train is a system of interconnected gears arranged so that the rotation of one of the gears leads to the rotation of all the gears. These gears drive something called an escapement, a disc with two tooth-like arms called pallets, mounted on a rotating shaft, that control the movement of the gears. This escapement is guided by another object called the regulator. In the earliest clocks, a horizontal cross-bar with adjusted weights known as a foliot was used as the regulator. As the gear train moved the pallets, the escapement moved the bar back and forth. The weights on the foliot resisted sudden changes due to rotational inertia, thereby regulating the movement of the gear train. The regulated motion of the gear train was finally transferred to an indicator, in the form of hands, which displayed it in the form of passage of time on the clock’s face. These types of clocks created a revolution in horology and were in continuous use till the 1800s.
Chapter 5: Pendulum Clock (1656 – 1930 CE)
The mechanical clocks, although far superior to their predecessors, had a major disadvantage. Their regulators worked on rotational inertia, depending on the movement of the gear train; thus, their accuracy reduced with time and needed to be readjusted. In 1656, the Dutch mathematician and engineer Christiaan Huygens invented the pendulum clock. It had almost the same design and principle as that of the mechanical clock, except for the regulator part. Instead of the dependent foilot, a pendulum was used as the regulator. Unlike the foliot, the pendulum works on the principle of simple harmonic motion under gravity. The pendulum thus swings in a uniform motion independent of any external object. Thus, the pendulum clock worked as a far better-regulated and, in turn, more efficient clock than the mechanical clock. Another innovation was that the power source was changed from a falling weight to a spring whose potential energy provided the power. The pendulum clocks were in common use till the late 1930s.
Chapter 6: Marine Chronometer (1735 – 1970 CE)
The Pendulum Clock, although very efficient and requiring very little calibration, had a major drawback. It was inefficient in sea voyages, as the motion of the pendulum was interfered with by the constant rocking and rolling of the waves. In 1735, the English engineer John Harrison invented the marine chronometer, suitable for sea voyages. The marine chronometer had a balance wheel and a spring in place of a pendulum as the regulator. The wheel oscillated in a uniform harmonic oscillation, and the spring attached to it provided the elasticity, thereby maintaining a uniform regulation independent of both gear train motion and motions from sea waves. The marine chronometer proved to be very efficient in naval expeditions and warfare, and continued to be used till the 1970s, when they were replaced by atomic clocks.
Chapter 7: Quartz Clock (1927 – present)
The Quartz Clocks are the first electrical clocks. Here, the power sources are batteries, in place of springs or weights. But the most important innovation is in the regulators. Quartz is a crystal that possesses a unique property called piezoelectricity, the ability to generate electrical pulses when under mechanical stress. Thus, in quartz clocks, tuning forks made of quartz crystal are installed in vibrated conditions, thus creating electrical pulses which act as the regulator. Electrical clocks are far superior in accuracy and efficiency compared to mechanical clocks, and thus, the former completely replaced the latter within decades. Also, quartz being extremely abundant on earth, made quartz clocks extremely cheap, and thus they are still in use in nearly every household.
Chapter 8: Atomic Clock (1949 – present)
Atomic Clocks are the champions of accuracy. In an atomic clock, the quartz crystal vibrates and sends electrical signals at a fixed frequency. These electrical signals are then converted to microwave signals. These microwave signals are sent to certain atoms: either Cesium-133, Rubidium-87, or Hydrogen (maser). The microwave signals excite the atoms. These atoms pass through a detector. Any change in the frequency of the electrical signal will change the level of excitation of the atom. The detector will detect the change and send a feedback signal to the quartz, thereby maintaining the regulating frequency. These clocks are so accurate that time has been defined by them. Before the atomic clocks, time was defined by the Earth’s rotation and revolution, whose measurements were affected by tides, earthquakes, and other causes. But after the invention of the Atomic clocks, one second is defined as 9,192,632,770 oscillations of radiation corresponding to a specific energy in the Cesium-133 atom. So, with the invention of atomic clocks, the calculation of time became finally independent of the Earth’s surface. Atomic clocks are now used in global navigation systems like GPS, telecommunication and internet facilities, stock markets, astronomical observations, and many more.
Chapter 9: Smart Watch (2000 – present)
Smart watches are direct descendants of Quartz clocks. The main body is the same except that the electrical signals are passed through a digital logical counter, which counts the oscillations. The software associated with it compares the oscillation with an external timeframe (GPS, phone, satellite, etc.) and sends feedback signals to the quartz crystal. Another thing that changed is that smart watches have a digital display frame with no clock hands as an indicator. Except for the regulator, almost all the mechanisms are the same for a smart watch and a quartz watch with a digital frame. They are today used both as timekeeping devices and for external features like measuring heart rate, weather reports, etc.
Conclusion
Clocks have evolved along with human civilizations over time. From calculating time to defining time, they have come a long way. The evolution can be classified into three different stages: pre-mechanical, mechanical, and electrical clocks. A proper electronic age for a clock is yet to come (if we don’t count mobile phones and personal computers as electronic clocks).
That is all for this blog. Hope you enjoyed it. Finally wrote my first “technology” blog after 36 blogs. So, kindly forgive the technical jargon. I will try to minimize them in the future. Will be bringing more blogs on the history of science and technology like this. Please like, share, and subscribe if you want to get updates for my blogs. And thank you for reading the piece.