The Human Illusion of Time

6. Late Middle Ages

In the late Middle Ages, humankind continued experiments with mechanical devices. Some experiments were aimed to create a device that could provide a mechanical process with a constant duration. It was the next step in organizing human life, but the creation of such a device had one big problem. As soon as any device begins to count the constant duration of any physical process, its indications become usable for everyday life. However, an indication of that device becomes contrary to the indication of ancient seasonal hours because the indication of seasonal hours depends on the duration of a sun day. Hence, indications of any device using a constant duration process and seasonal hours differed. As soon as they use mechanical devices with a constant duration process to estimate seasonal “hours,” they have the following question. How is it possible to unify the readings of two devices that use different principles of action to make the “right” estimation of “hours”?

That was not an easy question because humankind had never faced such a problem. To find an answer to that question, they need to make some technology that can unify processes with ever-changing duration and mechanical processes with a constant duration. Moreover, a mechanical device becomes operational at night. Hence, many questions arise for “night hours”. What indication of “hours” must be at night? How many hours can it show at night? Is the “night hour” equal to the duration of the “day hour”? (and so on)

To produce a mechanical device with a constant duration process usable for indication of “hours,” each hour must have the same duration as any other. Therefore, the duration of a day was incomparable to the estimation of that duration. They need to have a different process in nature that has a constant duration during the day and night. That process was successfully found. It was the duration between any given noon and the following noon. Despite the different angles between the horizon and the sun at noon on different days, the duration between two subsequent noons is ever constant. Hence, humankind reverts to celestial processes to estimate constant duration processes.

Moreover, celestial processes show one more helpful aspect. Despite the different day-night durations across a year, there are two specific days that have equal day-and-night durations. Those are equinoxes.

Suppose a day's duration equals a night's duration at each equinox. In that case, an exact number of "hours" can be used to estimate the duration for both processes. Moreover, each hour's duration becomes equal to any other hour's at each equinox, even for seasonal hours. Those duration combinations become appropriate for comparison with a device with a constant duration of mechanical process. Hence, each mechanical device can be calibrated for one "hour" or seasonal hour on the day of any equinox. In that case, an indication of the mechanical device must be adjusted so that the duration of twelve "hours" indication of that device becomes equal to the duration of a whole day of an equinox measured by seasonal hours. As a result, an indication of another twelve "hours" indicates night "hours" for that mechanical device, and the total duration between two subsequent noons becomes twenty-four hours. Thus, standard duration and calculation methods were invented for all hours, day and night.

Everything went well, but that method of estimation and calculation for hours caused one more question. Ancient seasonal sundials indicate hours as soon as the Sun rises above the horizon. Unlike seasonal hours, a device with a constant duration of the mechanical process begins its indication at noon. Therefore, a variable difference in a few hours appears between an indication of the seasonal sundial and a mechanical device. They need to take one more step to find a solution to that matter because mechanical devices based on mechanical processes with constant duration can work at night. It seemed more useful than ancient seasonal hours. Thus, mechanical devices had priority.

They decided (it was a human discussion) to begin calculating "hours" each day from noon. It was a revolutionary idea that stayed contrary to any previous human experience to start the calculation of day hours from sunrise. To keep that helpful system, they need to estimate noon (an event that appears as soon as the Sun crosses the celestial meridian). That procedure required specific devices and activity from humans, and it was not as easy as estimating the beginning of sunrise. Moreover, it led to the recalibration of all sundials to make their indication equal to that of mechanical devices. It was a true innovation. However, a new idea was widely accepted and gave way to the creation of clocks.