Sundials of various forms have been around for thousands of years, but these days they are more often than not used as a part of the garden decor rather than a gadget to tell the time. Often decorative sundials will have a motto inscribed on the face and a couple are from the article I found:

“I stand amid the summer flowers
To tell the passage of the hours”

“I am a sundial, and I make a botch
Of what is done far better by a watch”

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

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

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Image source jofo2005

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