19 July

Seasonal hours. The Babylonians and others, instead of doing something stupid like moving their clocks back and forward by an hour twice a year, instead allowed the length of their hours to vary with the season, defined by the sun and sundials. There were always 12 hours in the day, but the length of the hours themselves changed. Not that this was necessarily their concern, but this prevents the sharp (and very unhealthy) shock to the system from shifting clocks twice a year. The picture is a tablet they used to do these calculations.