The word "hour" comes from the Greek, meaning, "season". Early measurements of time derived from the sun. On sundials built by ancient Egyptians, Babylonians, Greeks and Romans, 12 scratches divided the circle described by the sundial pointer's shadow. The actual time taken for the shadow to cover one interval varied from season to season, according to how high the sun rose in the sky. These were "temporary (or seasonal) hours".
Not until the 13th century did the Arab mathematician Abu el-Hasan develop hours of a fixed duration, using the principles of trigonometry to regulate these intervals. There followed the earliest mechanical clock, erected in Milan in 1335, and pocket watches, first manufactured in Germany soon after 1500. Errors in these early timepieces could run to as much as half an hour a day. Nowadays, precision atomic watches can measure nanoseconds - millionths of a second.
By the time Salvador Dali (1904-1989) painted 'La Montre Molle' (The Soft Watch), the timekeeping demands of the Industrial Revolution had seen public clocks installed in every building and pocket watches in every businessman's fob. People were in a hurry. Dali's painting, which summons up all our unease about our own mortality, contrasts the softness of our living bodies with the unyielding ticking away of their decay. What are we in a hurry for? To what end?
"We set spies and watches on the Sun. We make Time give an account of itself, and shall we not give an account of Time?" wrote the poet Coleridge in his notebooks in the summer of 1807.
However you measure it, time is always passing.