Jul 26, 2011
Seven Wonders of the Industrial World - Part Two
The Bell Rock Lighthouse, lying approximately 12 miles off the coast of Angus, Scotland, is the oldest existing sea-washed lighthouse in the world. It was also the last sea tower to be built in the days of sail. Bell Rock, also known as Inchcape Rock, is a long and treacherous sandstone reef lying in the North Sea, which, except at low tides, lies submerged just beneath the waves.
According to legend, the rock is called Bell Rock because of an attempt by the abbot from Arbroath, in the 14th century, to install a warning bell on it. The bell lasted only one year before it was stolen by pirates. This story is immortalized in The Inchcape Rock, a famous poem by 19th century poet Robert Southey.
By the turn of the 18th century, it was estimated that the rocks were responsible for the wrecking of up to six ships every winter. In one storm alone, 70 ships were lost off the east coast of Scotland.
Scottish engineer Robert Stevenson proposed the construction of a lighthouse on Bell Rock in 1799. To build a permanent beacon that would warn ships to keep away from this rock was both a challenge and an obsession for Stevenson.
He became an engineer for the Northern Lighthouse Board in 1797, inspecting the few warning lights for seafarers that then existed along the Scottish coastline. These were often no more than coal braziers, and the resulting spoil from wrecked ships was a lucrative business. Most of the coast was in darkness.
Stevenson was convinced he could improve on these primitive lights. It took a year to find anyone brave enough to risk taking him to Bell Rock, but when he finally surveyed the reef in the summer of 1800, he devised a plan for a substantial stone tower.
Cost concerns and the relatively radical nature of his proposal caused it to initially be shelved. However, the loss of the warship HMS York and all on board in 1804 resulted in an uproar in Parliament which eventually led to legislation being passed in 1806 enabling construction to begin.
Stevenson drew the inspiration for his lighthouse design from the Eddystone Lighthouse, off the coast of Cornwall. Built 50 years earlier by John Smeaton, this was a milestone in lighthouse design. Shaped with the now classic wide base, tapering to a narrow tower, it was the only off-shore structure that had until then managed to survive for any length of time against the constant battering of the seas.
Stevenson elaborated on this design. His lighthouse would have to be higher, over 30m (100ft), if it was to survive the waves of the North Sea. He also incorporated more efficient reflectors, using the latest oil lighting technology, which would make his beacon the brightest yet seen.
It was the challenges faced in the building of the lighthouse that led to it being described as one of the Seven Wonders of the Industrial World. Work could only be done during the calm summer months, and even then work was limited to the two hours at low tide. In between, the workers Stevenson recruited waited, living at first on a ship, then later in a temporary barracks built on stilts above the rock.
Work was slow and laborious. They used simple pickaxes, which needed constant re-sharpening by a smithy, who often worked up to his knees in freezing water. Stevenson could not afford to use gunpowder for fear of damaging the rock itself.
The foundations and beacon legs were raised during the first season. During the winter, stonemasons cut rocks for the lighthouse out of Aberdeen granite. During the spring of 1808, work resumed. The temporary barracks was completed and the first three courses of stone were laid. In the whole of the second season, there were only 80 hours of building work completed on the rock.
The masonry work on which the lighthouse rests was constructed to such a high standard that it has not been replaced or adapted in 200 years. Bell Rock Lighthouse stands 115 feet in height and 42 feet in diameter at the base, tapering to 15 feet in diameter at the top. It is of solid dovetailed masonry for the first 30 feet, half of which is below high water and above are five chambers and the light room. A total of about 2500 granite stones were used in its construction.
The original optical system used at the Bell Rock consisted of twenty four parabolic reflectors 25 inches in diameter with their inner surfaces silvered to better reflect the light. The reflectors were arranged in a rectangle with seven located on each of the major sides. The ten reflectors on the minor sides had red glass discs fitted to the outer rims. The whole apparatus revolved by the action of a clockwork arrangement powered by a weight descending through the tower. As the optical system revolved a distinctive pattern of alternating red and white light was seen. This was the first revolving light in Scotland. The 24 great lanterns were lit for the first time on 1 February 1811.
The lamps and reflectors were replaced in 1843, with the original equipment being used in the lighthouse at Cape Bonavista, Newfoundland where they are currently on display. The new mechanism in the Bell Rock had fully equalised light beams. About 1877, paraffin oil replaced the use of spermaceti oil. In 1964 a more efficient light mechanism was installed using electric light. On the 26th October 1988 a Dalen optic was installed, replacing the existing electric light of 1964 and the lighthouse was de-manned. This type of light, named after its Swedish inventor, flashes white - every 5 seconds - and has a nominal range of 18 miles. Remote electronic monitoring takes place from the Northern Lighthouse Board Headquarters in Edinburgh.