Privileged time
General mechanical engineering - General dynamics. Vector form

Subjectively, we recognize 3 attributes of time: simultaneity, order of succession, duration. These notions are well represented by devices that we generally call clocks. We are convinced that certain physical phenomena to which these devices give rise reproduce themselves identically, and we call them periodic. Among these phenomena, we must choose one. For a long time, the Earth's rotation, assumed to be uniform, represented the world clock.