Measuring time

The March of Time. Top left: Observing the length and angle of the sun's shadow cast by an upright stick. Top centre: The Tower of the Winds in Athens built by a Macedonian astronomer around 50 BC, with its elaborate weather vane and various sundials on the outside, and inside an elaborate astronomical clock driven by water power. Right, from top to bottom: A portable sundial from about 1560 with dials on all four sides and the top. A set of four sandglasses in ebony and ivory, probably Italian, dated about 1720. Each glass measures a quarter of the passing hour. An astronomical timepiece made by the Elizabethan clockmaker, Vallin, in about 1600. It shows the time, sun, phases of the moon and London high tide information. A modern Hewlett-Packard atomic clock using Rubidium radiation and a quartz crystal to measure time with incredible and continuous accuracy. Original artwork for the illustration on pp24-25 of L&L no. 598 (30 June 1973).