is Smeaton's most celebrated achievement, and the commission marked an upturn in both his fortunes and his reputation. Using manpower alone, over 40 years before battery-powered electricity became available, he designed and built a stone tower 22.5km from land on a tiny rock only accessible at low tide in summer. His ideas were to influence the design of lighthouses for the following 150 years.
Smeaton's lighthouse was the third on the site. The first was Winstanley's timber structure of 1696-98, which was destroyed in a storm in 1703. The second was also of timber, designed by silk merchant John Rudyerd and built 1708-9. This burnt down on the 2nd December 1755, precipitating Smeaton's commission. He was recommended by the then President of the Royal Society, even though he had been practising engineering for just a few years and was not well known.
Both earlier structures had been built of timber with granite ballast, the idea being that timber would move under wave action rather than resist it. Smeaton, the first engineer to consider the problem, decided to build in stone he believed that the sea must give way to the building. He took inspiration from both the shape of an oak tree trunk and the interlocking stones of London pavements. He then had to convince Josias Jessop (c1710-61) surveyor of the Rudyerd lighthouse and later Smeaton's assistant of his ideas.
Smeaton mapped the surface of the rock in April 1756 using an early theodolite. Instead of blasting a level surface, he used the existing contours, and set about constructing the lighthouse substructure
by dovetailing the stonework into the living rock. The smooth tapering tower above was circular in section, offering as little resistance to the sea as possible. The lower part was solid, the upper hollow with four chambers, one above the other, for stores and the lightkeepers. The lamp consisted of two counterbalanced chandeliers each with 12 candles, housed in an octagonal lantern.
Meticulous planning was crucial as time spent on site was limited by tides, weather conditions and lack of space. In situ work was only possible in the summer months. Success depended on the quality of the materials, workmanship and preparation.
Smeaton sourced the stone himself Cornish granite (moorstone) for exposed parts, Portland stone (limestone) for the interior and Plymouth marble for the keystone joggles between courses. He set tight tolerances and, to ensure that he got and kept the best craftsmen, he paid generously, with premiums for working at sea. Preparation for each course meant trial fitting the numbered blocks on land before shipping them to the reef for reassembly and grouting.
Furthermore, he realised that the mortar joints might compromise the integrity of the tower. With the help of William Cookworthy (1705-80), pioneer of English porcelain, he experimented with lime and pozzolana (volcanic ash) mixes to find a mortar that would set as hard as stone in wet conditions a forerunner of modern concrete mixes. He settled on equal parts lime and pozzolana mixed with a minimum of water (fresh or salt water produced the same result).
He also invented a lifting device for raising heavy loads from ships at sea to considerable heights, which has never been bettered, and installed one of the first lightning conductors in Britain. Smeaton knew of Benjamin Franklin's (1706-90) work and had observed lightning damage to Lostwithiel church in 1757.
During this period, there was conflict between England and France and Smeaton's workforce was prey to Navy press gangs, until 1757 when silver medals of exemption were issued to his workers. The medals bore the legend In Salutem Omnium Edistone Resurgit (For the Safety of All Eddystone Rises Again) and an image of the lighthouse, which was also painted on the sails of the supply vessels.
Smeaton lodged with Cookworthy in Plymouth but he made regular trips to London to see his wife and visit the Royal Society and Trinity House, who had provided a light ship anchored near the reef. Ann Smeaton would show people the lighthouse model and explain it to them.
The first stone was laid on 12th June 1757. By 17th August two years later, the stonework was up to cornice level. On 17th September the cupola of the lantern was hoisted into place and Smeaton, teetering on planks, fixed the burnished gold-plated copper ball to the top of the lighthouse, some 37m above the sea. The lamp was lit on 16th October. Amazingly, there was no loss of life or limb during construction: one man broke his leg and Smeaton dislocated a thumb.
The intrinsic weakness of the Eddystone rock and the discovery of a cave beneath the tower eventually led to the construction of another lighthouse on a neighbouring rock. Smeaton's tower was removed and the upper part re-erected on Plymouth Hoe (1882-84).
Smeaton's other lighthouse project was the Spurn Point Lighthouses
, located on the north side of the mouth of the River Humber, marking a dangerous sand spit. The designs for both lighthouses, which are founded on timber piles, were approved by Trinity House on 21st February 1767. The previous lights were removed that season but it wasn't until 1771 that work began, by which time the spit had moved and the position of the lower lighthouse had to be changed.
The lower light tower was completed in December 1773 but a storm in January 1776 exposed part of its foundations, necessitating remedial works. Both coal-fired lights were lit on 5th September 1776, and Smeaton certified completion on 7th April 1777, remarking on one site visit that although "the brick-work of both houses is somewhat rough ... I have no doubt of the firmness of the work".
main references BDCE1
painting of Smeaton
courtesy Institution of Civil Engineers