Timepieces From shadow on sand to atomic clocks — humanity's chase of ever-more-precise time. 3 posts· 3500 BCE – 250 BCE Ctesibius's clepsydra, or the water clock that fixed itself 250 BCE The Egyptian clepsydra, or how priests told time without the sun 1500 BCE The shadow clock, or how Egypt turned sunlight into hours 3500 BCE
