Thomas Ogren

So wrote Hilaire Belloc, but is this really fair? Sundials are earliest known form of time-keeping having been used for some five thousand years. The Greek historian Herodotus stated that sundials were first used by Chaldeans and Sumerians in Babylonia which was part of modern Iraq. They used vertical rods on their buildings and noted position of shadow to record passing of hours. The concept was developed by Greeks and Romans who constructed various different shapes of dial to enable them to tell time and season of year. Usually these were bowl-shaped dials with vertical or horizontal gnomons (shadow-casters) and hour lines marked in hollow of bowl. Over years more elaborate designs were produced until advent of accurate clocks when function of sundial became more decorative than as a reliable means of telling time.

The question is often asked "Can a sundial really tell correct time?" to which you will receive Alice in Wonderland reply that it depends upon what you mean by "the correct time". Our clocks and watches work on basis of there being exactly twenty-four hours between one day and next but, because of eliptical nature of earth's orbit around sun, time shown on sundial will vary according to seasons. In February by clock sun is almost fifteen minutes slow, whereas during spring and summer months it gains and loses between four and six minutes in two cycles. At other extreme in November sundial appears to be some seventeen minutes fast. In fact sundial is accurate on only four days of year, about April 15, June 14, September 2 and December 25. Some sundials include a table showing deviation from "clock time" according to date.