Inscribed stone in Farranreagh

Inscribed slab known as an Altazimuth Stone, described by Michael Egan of Knightstown as; 'In an area of ground known as the Pond Field, Knightstown, Valentia Island lies a Valentia Slate slab. The slab is in the shape of an equilateral triangle, each side measuring 42 inches(1.06m) x 3 inches (0.07m) thick. It has laid there since 1862. Engraved on that stone are the words GREAT EUROPEAN ARC OF LONGITUDE  SITE OF THE POSITION OF THE ALTAZIMUTH  USED  IN THE DETERMINATION OF THE LONGITUDE OF VALENTIA IN 1862. There are only two such stones in the World, the second one being in the Ural Mountains, Russia. For hundreds of years navigation had the lines of latitude, the sun, moon, stars and the land (when they were within sight of such land) to navigate. When clear of land and without the sun, moon and stars, which would be quite regular, all that was left was Latitude which was in no way accurate for shipping,  “dead reckoning” was not good enough. In other words ships were lost and only got to their destination if they were lucky. The vital missing piece were the lines of longitude. In 1714 the British Government brought in the Longitude Act offering £20,000 to anyone who would solve the longitude question. John Harrison invented a clock which would stand up to extreme heat, extreme cold and would not be affected by ship’s movement of any kind. There was then another problem, namely, where to place the prime meridian, the zero-degree longitude line. It was settled finally at Greenwich, London. When it  was settled in Greenwich, the lines of longitude had to be sorted out going east and west and this is where the Valentia Altazimuth Stone comes in. It took time and knowledge to carry out the experiment using an instrument called the Altazimuth, derived from two words Altitude and Zenith (basically a telescope with readings vertically and horizontally) in conjunction with the stars and the underwater cable from Valentia Island to the UK at that time. When that experiment was successfully completed, a Stone, as mentioned above, was placed in that spot surrounded by a small concrete wall and iron railings. A similar experiment took place in the Ural Mountains, Russia. Valentia was used in that it was the furthest point west and the Ural Mountains was used as it was the most eastern point in Europe with an Altazimuth Stone, east and west, just two in the world thereby allowing the lines of longitude to be marked out'. Comp[iled by: Caimin O'Brien based on details provided by Michael Egan