Summertime, wintertime, a biannual shift or what?

Until the fourteenth century human activities were coordinated by the seasonal changes of sunrise and sunset. The day and the night were each divided into 12 h with the day beginning at sunrise and the night at sunset. Thereby, the hours of the day were shorter in winter and longer in summer whereas for the hours of the night the opposite holds. Only at the two equinoxes of a year were the hours of day and night of equal length. From a physiological perspective these were golden ages, as adjustment of the body clock with dusk and dawn triggering melatonin offset and onset could be aligned with the activity cycle. It seems that two processes initiated a change in time perception and meaning. One was the intention of monasteries to coordinate the regular prayers, thereby introducing more precise clocks independent of the length of daylight, and the astronomers, especially in the Islamic world, who needed more precise clocks for registering astronomic events and sharing their observations. During the fourteenth century everywhere in Europe on churches and towers (one-handed) clocks were installed with acoustic means like chimes informing the public which hour it is. From then on civil life became coordinated by these technical innovations. City doors were opened at fixed hours and commercial life became synchronized. Technology overtook physiology. …