Outsize objects

Sule Skerry is the most remote lighthouse in Scotland. Forty miles west of Orkney, and a similar distance north off the coast of Sutherland, it is yet directly in the path of vessels making their way through the Pentland Firth to or from the Iceland seas. It was built over two years, because the length of the days at such a northerly latitude meant that darkness fell early, and the winter weather was extremely stormy. The lens was the largest owned by the Lighthouse Commissioners, due to the importance of Sule Skerry as a landfall light for vessels approaching from the Atlantic.

The enormous lantern, sixteen feet in diameter, was placed on top of an 88 feet tower, and the new light could be seen at Cape Wrath, 35 miles away, on 60 nights in its first three months of operation.

The families of keepers based here were housed in Stromness from 1895 until automation in December 1982. The hyper-radiant lens was removed and presented to National Museums Scotland in 1978. It has been replaced by a Dalen Operated gas light with a fourth order lens.

The first foghorn – after experiments with bells, gun-fire, horns and gongs – was installed at St Abbs Head as late as 1876. Those at Ailsa Craig (1886) were worked by compressed air operated by gas engines, while that at Rattray Head (1895) influenced the design of the lighthouse itself.

The mournful wail of the foghorn, particularly when heard through an east coast ‘haar’, could send shivers up the spine of those who lived close to the sea. But when in 1899 the Inchkeith foghorn sounded more or less continuously for 130 hours, those who lived on the Fife coastline were less than amused.

A few years earlier, in 1885, the Commissioners had used their powers of compulsory purchase on the island of Fidra to acquire land for a lighthouse, and the Dirleton Estate made a claim for compensation for damages through possible foghorn use. However, the Court of Session found that protection of life at sea was more important than the possibility of ‘harsh or disagreeable sounds occurring now and then.’

By 2005, the Northern Lighthouse Board reviewed all its Aids to Navigation (AtoNs), including foghorns. ‘The conclusion was that audible fog signals had a significantly reduced role in the modern marine environment, as a result of the widespread use of electronic position finding aids and radar, and the adoption of enclosed bridges on many vessels.’ The very last Scottish foghorn was switched off on 4 October 2005 at Skerryvore lighthouse.

Nearly all Robert Stevenson's lanterns, with their rectangular-paned framed glazing panels, were replaced with the new triangular structures introduced by Alan Stevenson when their reflectors gave way to more efficient lenses.

When the 1833 lighthouse at Girdleness was modernised in 1847, the upper lantern was not destroyed. Instead, it was shipped to Inchkeith Island in the Firth of Forth, where it was set up some distance from the main 1804 lighthouse and used to shelter experimental optics and lamps from the elements. Here some of Thomas Stevenson’s important developments on holophotal glass optics were tested.

The cast iron structure consists of 80 parts, with 200 fittings, and is decorated with motifs symbolising the Northern Lighthouse Board’s work to make navigation safe around the hazardous Scottish coastline.

The whole of the light from the burner is condensed into a horizontal arc of 45º, using a third-order Fresnel fixed light apparatus and annular lens, held in a bronze frame on three pillars.

The frame has eight straight condensing prisms held vertically on either side of the ‘bull’s-eye’, which has nine elements below it and 12 elements above, all throwing the beam out in front. At the back of the optic, there are six part and 10 horizontal curved prisms in a semi-circle, which return the light forward; the light rays which pass above this, pass through the five conoidal right-angled prisms held above the main optic, and then forward.

‘The whole light is spread with strict equality over the 45º by means of the five optical agents described,’ wrote Thomas Stevenson, ‘involving in no case more than four refractions and four total reflections.’ This is the ‘full-sized model’ displayed at the Paris Exhibition of 1867, and thus was never used in a lighthouse.

Faraday did not develop systems of electrical light for lighthouses, but was asked to investigate those proposed by others, and one reasonably-successful system was proposed in the late 1850s by Frederick Hale Holmes (c.1811-1870). This used a carbon arc lamp, with its power generated from an electromagnetic machine driven by a steam engine. Earlier attempts had been fuelled by batteries, which were quickly drained.

After considerable testing by Faraday, Holmes’s system was installed in the South Foreland lighthouse and first shone on 8 December 1858. Although it was not continuously used over the next few years, it was modified so as to ensure its effectiveness.

In 1871, a new alternating current machine devised by Holmes was installed, the machine you see here. Faraday undertook much of the monitoring of the light, visiting South Foreland in all weathers and frequently going out to sea to observe the light. Although electric lights were installed in other lighthouses, the programme was deemed a failure due to the expense involved and in 1880 electricity at South Foreland was abandoned.