Lighthouse

History of lighthouses

From Wikipedia, the free encyclopedia     

Tower of Hercules, a Roman lighthouse at La Coruña modelled on the Pharos.

 

The history of lighthouses refers to the development of the use of towers, buildings, or other types of structure, as an aid to navigation for maritime pilots at sea or on inland waterways.

Premodern era

Before the development of clearly defined ports mariners were guided by fires built on hilltops. Since raising the fire would improve the visibility, placing the fire on a platform became a practice that led to the development of the lighthouse. In antiquity, the lighthouse functioned more as an entrance marker to ports than as a warning signal for reefs and promontories, unlike many modern lighthouses.
                                                                                   

Greek-Roman period

Graphic reconstruction of the Pharos according to a 2006 study.

Written descriptions and drawings of the Pharos of Alexandria provide information about lighthouses, but the tower itself collapsed during an earthquake many centuries after its construction in the 3rd century BC by the Greeks. The intact Tower of Hercules at La Coruña and the ruins of the Dover lighthouse in England give insight into construction; other evidence about lighthouses exists in depictions on coins and mosaics, of which many represent the lighthouse at Ostia. Coins from Alexandria, Ostia, and Laodicea in Syria also exist.
                                                                                      

Europe

Engraving of the Cordouan tower completed in 1611

During the middle age times, Roman lighthouses fell into disuse, but some remained functional, such as the Farum Brigantium, now known as the Tower of Hercules, in A Coruña, Spain, and others in the Mediterranean Sea such as the Meloria Tower at Genoa. As navigation improved, lighthouses gradually expanded into Western and Northern Europe.^[1] One of the oldest working lighthouses in Europe is Hook Lighthouse located at Hook Head in County Wexford, Ireland. It was built during the medieval period, in a sturdy –circular design.

  

Modern lighthouses

Construction

The modern era of lighthouses began at the turn of the 18th century, as lighthouse construction boomed in lockstep with burgeoning levels of transatlantic commerce. Advances in structural engineering and new and efficient lighting equipment allowed for the creation of larger and more powerful lighthouses, including ones exposed to the sea. The function of lighthouses shifted toward the provision of a visible warning against shipping hazards, such as rocks or reefs.
                                                                                   

Further development

Bell Rock Lighthouse constructed on a dangerous rock submerged at most states of the tide

Scottish engineer Robert Stevenson was a seminal figure in the development of lighthouse design and construction in the first half of the 19th century. In 1797, he was appointed engineer to the newly formed Northern Lighthouse Board, the Lighthouse Authority for Scotland and the Isle of Man. His greatest achievement was the construction of the Bell Rock Lighthouse in 1810, one of the most impressive feats of engineering of the age. This structure was based upon the design of the earlier Eddystone Lighthouse by John Smeaton, but with several improved features, such as the incorporation of rotating lights, alternating between red and white.

Lighting improvements                 

Argand lamp with circular wick and glass chimney. (Illustration from Les Merveilles de la science [1867-1869] by Louis Figuier).

The source of illumination had generally been wood pyres or burning coal but this was expensive, some lighthouses consuming 400 tons of coal a year. Candles or oil lamps backed by concave mirrors were used, often in large banks. The French conducted a series of tests between 1783 and 1788 with varying results. Smeaton's Eddystone lighthouse used 24 candles until 1810.

Optics

Diagram depicting how a spherical Fresnel lens collimates light.

With the development of the steady illumination of the Argand lamp, the application of optical lenses to increase and focus the light intensity became a practical possibility. William Hutchinson developed the first practical optical system in 1763, known as a catoptric system. He constructed paraboloidal reflectors by attaching small pieces of reflective material to a cast that had been moulded into an approximate paraboloid. This rudimentary system effectively collimated the emitted light into a concentrated beam, thereby greatly increasing the light's visibility. His system was installed in the newly built Leasowe Lighthouse, and was later copied elsewhere.^[31] The ability to focus the light led to the first revolving lighthouse beams, where the light would appear to the mariners as a series of intermittent flashes. It also became possible to transmit complex signals using the light flashes.

   

5. References

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6. Crompton, Samuel, W; Rhein, Michael, J. The Ultimate Book of Lighthouses. San Diego, CA: Thunder Bay Press, 2002. ISBN 1-59223-102-0
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8. Beaver, Patrick (1971). A History of Lighthouses. London: Peter Davies Ltd. p. 17. ISBN 0-432-01290-7.
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10. Stevenson, D. Alan (1959). The world's lighthouses before 1820. London: Oxford University Press. pp. 32–33.
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12. Russ, Rowlett (2005). "Lighthouses of France: Aquitaine". Retrieved Jul 15, 2015.
13. 
    
Bathurst, Bella (2000). The lighthouse Stevensons. New York: Perennial. p. 135. ISBN 0-06-093226-0.