Knowledge of time The usefulness of the number 3

— Every civilisation has its magic numbers, whether lucky or unlucky. What about “3”? It is quite simply the basis of our time calculation system and has indeed been so for thousands of years.

Chiffre 3

Knowledge of time is of course a fundamental need. Without it, just imagine the consequences on our means of communication! On various levels, this need has always existed and gave rise to the division of time, particularly that of the day – a practice that our modern timekeepers have rendered increasingly rigorous. Nonetheless, these instruments as such are fairly recent: for centuries, man made do with very simple means to divide up the day that could be found in his immediate surroundings.


Gnomon. © DR

The first of these means was the gnomon. The word comes from the Greek (meaning indicator), but its use dates back well before the Green civilisation, since it already appeared in China during the Yao period, 24 centuries BC. It was originally a stick placed in the ground. According to the length of the shadow it cast, people determined the period of the day between the rising of the sun, its zenith (noon) and its setting. People also realised that the length of the shadow also varied in step with the seasons, and thus began marking off increasingly accurate graduations on the ground. This method enabled for example the builders of Stonehenge in the south of England to point their temple towards the sunrise on the day of the summer solstice, meaning the longest of the 365 days in a year. That was way back in 2700 BC…


Stonehenge. © DR

More recently, around 600 B.C., man had the idea of incorporating the gnomon into a dedicated construction that we refer to as a sundial and is also found across all civilisations. In India, for example, the Jaipur Observatory (1724 AD) harbours an astonishing number of all kinds of sundials. Under the influence of the Babylonians (in what is now Iraq), whose system of calculations and trade was based on the number 3 and its multiples since 2000 BC, the day was divided into 12 periods on most sundials in Europe and the Middle East. It is important to use the term periods and not hours, since the length of the day varies according to the system, which meant that the longer the day, the longer the period. The transition between these flexible periods and fixed-duration hours occurred only much later, when the first horological movements appeared in the 13th century. Nonetheless, some civilisations held onto the system of flexible periods until quite recently – such as Japan, which did not adopt fixed-length hours until 1873.


Sundials at Jaipur Observatory. © DR

Coming back to the sophisticated timepieces in our contemporary world, what do we notice about their dials? That they are divided into 12! In other words, when it comes to calculating time, we still resort to the 4000 year-old Babylonian system: 12, 24, 60 and 3600 are all multiples of 3. Go figure as to why the whole world uses such an antiquated method… Or why all attempts to convert time calculation to the decimal system have failed, apart from the modern division of the second. Perhaps the relationship between man and time goes well beyond the laws, systems or standards that have since been invented. It is also true that while man can influence many things about his environment, he has no hold on time. So perhaps he maintains a natural relationship with this phenomenon, just as back in the day when the 3 most important events of the day were the rising of the sun, its zenith and its setting. Back to the figure 3…