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17 April 2012
As an island nation, we in the UK are used to seeing lighthouses around our coasts, but have you ever stopped to consider when they were first built and how they worked in those early days?
The purpose of lighthouses is obviously to mark dangerous coastlines, rocks and reefs and to aid navigation, especially at night or in misty conditions.
The first known warnings made to boats of hazardous rocks and shores, were fires, set at the edge of the water, but it was in Egypt that we first heard of actual structures being built, which used light to guide ships.
Built on the island of Pharos, the lighthouse was commissioned by Ptolemy in 290 B.C. It took 20 years to build, and became the tallest building in existence, except for the Great Pyramid, standing at between 450 and 600 feet in height, and was recognised as one of the Seven Wonders of the World. It is thought to have cost around the equivalent of three million dollars or £2.8 million. Its design was nothing like the slim structures we are familiar with today. It consisted of three stages, the first being in the shape of a massive box built on a 20 foot high stone platform. On top of this was an eight sided tower, followed by a cylinder that extended to an open cupola where the fire burned to provide the light. On its roof was a large statue, thought to be of the sea god Poseidon. The fire's light was believed to have been projected into a beam by the use of a large curved mirror, probably made of polished bronze. It was said that ships could detect its signals up to 100 miles away, the light from the tower by night, and the smoke from the fire by day. This claim however seems a little excessive.
The lighthouse became so famous that the name "pharos" became the root of the word "lighthouse" in many languages. It stood for over 1,500 years, surviving a tsunami in 365 AD, but earth tremors resulted in cracks forming in the structure which needed restoration. Then, a major earthquake in the region, in the 14th century, caused such severe damage that the structure eventually collapsed.
In medieval times the Iranians apparently erected large minaret towers in the mouth of the Persian Gulf to aid navigation. In China, the medieval mosque at Canton also had a minaret serving as a lighthouse, and in 1165 a pagoda known as the Liuhe Pagoda, was built in Hangzhou and acted as a lighthouse for sailors in the Qiantang River.
One of the oldest working lighthouses in Europe is Hook Lighthouse, constructed at Hook Head in County Wexford, Ireland in 13th century and built in circular design. Two lighthouses, called the Pharos, were built at Dover (UK) soon after the Roman conquest of Britain. They were constructed on two heights (the Eastern and the Western). The one on the Eastern Height still stands in the grounds of Dover Castle.
Another famous early Roman lighthouse is the Tower of Hercules, probably built in the first century, on a peninsula at A Coruna in north-west Spain. It was originally known as the "Farum Brigantium", the Latin word farum being derived from the Greek pharos. The light was originally produced using a wood fired system located on the summit platform, but the lighthouse was abandoned after the Viking Invasions of 854-56. It was restored in the 14th century when the town became one of the kingdom's largest ports, and by the 17th century it had been fitted with a dome shaped lantern. More restoration was completed in the early 18th century, and in 1847, a system using Fresnel lenses (see later) was installed. It was electrified in 1926, with a beam visible for up to 32 nautical miles and is the oldest Roman lighthouse in use today.
Some early lighthouses used wick lamps as a light source and often the beam could only travel a few miles. The Argand hollow wick lamp and parabolic reflector were developed in Europe around 1781, while in the USA, whale oil was used with wicks until the Argand system was introduced around 1810,which was then later replaced with Colza oil (similar to rapeseed oil), lard oil and then Kerosene.
In 1822 a Frenchman, named Augustin Fresnel, found out how to increase the light intensity using prisms, and the first Fresnel lens was installed in 1822 in the Cordouan lighthouse in the mouth of the Gironde estuary. This light could be seen from 20 miles or 32 km away. By the 1860s, low-light-loss Fresnel lenses, much larger than the original ones, were in use in lighthouses around Britain and France, their use quickly extending to Italy and further afield to Australia and America. To create the flashing effect, designers had to come up with a way of making the lens revolve. This was done using a rotating stand with a clockwork mechanism with descending weights on cables. The keeper periodically cranked up the weight to the top of the lighthouse and as it descended, the lens revolved. The flashing effect was achieved each time a segment of the rotating lens passed between the lamp and the observer. The rate of rotation determined the frequency of the flash and made it possible for each lighthouse to have its own recognisable pattern.
Around the turn of the 20th century, acetylene gas (electricity and carbide) began replacing kerosene, and around 1910 many lighthouses began using the clever device called the Dalen Sun Valve, invented by the Swede, Gustav Dalen. The valve opened and closed the gas supply to the lamp according to how much sunlight it received, so the lights could be turned on automatically at dusk and off at dawn. Dalen also found out how to store the gas in tanks and to interrupt its flow, causing the light to flash. Dalen's inventions resulted in savings in fuel and maintenance, as the lamps only needed servicing twice a year.
As electricity became available, the clockwork mechanisms in the lighthouses were replaced by electric motors, with 100W bulbs providing the light source, and electronically operated fog signals were added. With all this electrification and automation, lighthouse keepers were sadly obsolete and from the 1980 they became superfluous to requirements. The last lighthouse in the UK to be automated was North Foreland in Kent, in 1998.
Many Fresnel lenses have been replaced by rotating aerodrome beacons which require less maintenance. The system of rotating lenses has in some cases been replaced by a high intensity light that emits short flashes, similar to the obstruction lights used to warn aircraft of tall buildings. Recent innovations include Vega Lights, (lighthouse beacons providing a range of up to 22 nautical miles with a 100 Watt lamp). They can operate in remote, solar-powered locations, on unattended sites, and require maintenance only once a year. There are in the region of 600 of these in operation around the world.
Technology moves on, and as new innovations such as GPS make navigation easier and safer, it may be tempting to think that lighthouses have had their day. Personally I'd prefer to have a reliable backup to my GPS, and there is nothing so comforting on your first ever night watch under sail, than to see the beam of a lighthouse shining through the darkness, to count the flashes and know that you are where you should be.
Author – Dee White
(Watch this space for further Lighthouse articles)
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