| "I am a sundial, and I make a botch | | | | should be set at the angle in degrees which |
| | | | is equal to the latitude of your location. |
| Of what is done far better by a watch" | | | | The sundial can then be fixed with the gnomon |
| | | | pointing to the Pole Star. There are various |
| So wrote Hilaire Belloc, but is this really | | | | ways of achieving this, the easiest of which, |
| fair? Sundials are the earliest known form of | | | | is to use a compass adjusted for the magnetic |
| time-keeping having been used for some five | | | | variation. Further details are beyond the |
| thousand years. The Greek historian Herodotus | | | | scope of this article, but for those |
| stated that sundials were first used by the | | | | interested look at this site. |
| Chaldeans and Sumerians in Babylonia which | | | | |
| was part of the modern Iraq. They used | | | | If you have read this far you will have |
| vertical rods on their buildings and noted | | | | discovered that there is a great deal more to |
| the position of the shadow to record the | | | | the sundial than a mere item of garden |
| passing of the hours. The concept was | | | | decoration. If this has piqued your interest |
| developed by the Greeks and Romans who | | | | in the subject, then you are not alone. There |
| constructed various different shapes of dial | | | | are Sundial Societies in countries around the |
| to enable them to tell the time and the | | | | world. The North American Sundial Society has |
| season of the year. Usually these were | | | | details of its objects and activities on its |
| bowl-shaped dials with vertical or horizontal | | | | website. |
| gnomons (shadow-casters) and hour lines | | | | |
| marked in the hollow of the bowl. Over the | | | | A number of sundial trails have been |
| years more elaborate designs were produced | | | | established. A good example is the Thames |
| until the advent of accurate clocks when the | | | | Sundial Trail in London, England. This site |
| function of the sundial became more | | | | lists a number of other trails in countries |
| decorative than as a reliable means of | | | | all over the world but only two in the United |
| telling the time. | | | | States. However the North American Sundial |
| | | | Society has a complete list on its website. |
| The question is often asked "Can a sundial | | | | |
| really tell the correct time?" to which you | | | | Two rather different designs are shown here. |
| will receive the Alice in Wonderland reply | | | | The first, which is commonly referred to as a |
| that it depends upon what you mean by "the | | | | Human Sundial, uses the person's shadow to |
| correct time". Our clocks and watches work on | | | | indicate the time. By standing in the |
| the basis of there being exactly twenty-four | | | | appropriate box for the date the shadow will |
| hours between one day and the next but, | | | | show the correct time. The second is a |
| because of the eliptical nature of the | | | | Digital Sundial which sounds like a |
| earth's orbit around the sun, the time shown | | | | contradiction in terms but in reality is just |
| on the sundial will vary according to the | | | | a rather clever design. |
| seasons. In February by the clock the sun is | | | | |
| almost fifteen minutes slow, whereas during | | | | Many sundials have a motto inscribed on the |
| the spring and summer months it gains and | | | | face. Often these are rather serious in tone |
| loses between four and six minutes in two | | | | and of the "Tempus fugit" variety but you |
| cycles. At the other extreme in November the | | | | also find some written in a lighter vein. |
| sundial appears to be some seventeen minutes | | | | Here are a few of my favourites: |
| fast. In fact the sundial is accurate on only | | | | |
| four days of the year, about April 15, June | | | | The shadow of my finger cast |
| 14, September 2 and December 25. Some | | | | |
| sundials include a table showing the | | | | Divides the future from the past |
| deviation from "clock time" according to the | | | | |
| date. | | | | The clock the time may wrongly tell, |
| | | | |
| The time indicated by the sun will also vary | | | | I never if the sun shines well |
| with the location of the dial. The sun | | | | |
| travels across the sky at the rate of fifteen | | | | I stand amid the summer flowers |
| degrees per hour so every degree of | | | | |
| longditude represents a difference of four | | | | To tell the passage of the hours |
| minutes from the standard meridian for the | | | | |
| region. The angle of the gnomon also depends | | | | And finally again from Hilaire Belloc: |
| on the situation, so to set up your sundial | | | | |
| correctly you need to know both the latitude | | | | I am a sundial, turned the wrong way round. |
| and longditude of its location. For the | | | | |
| United States and the United Kingdom this | | | | I cost my foolish mistress fifty pounds! |
| site can provide the information. The gnomon | | | | |