Eddystone Lighthouse

same as in the description

The Eddystone Lighthouse is a lighthouse that is located on the dangerous Eddystone Rocks, 9 statute miles (14 km) south of Rame Head in Cornwall, England. The rocks are submerged below the surface of the sea and are composed of Precambrian gneiss.

The current structure is the fourth to be built on the site.

This is probably the most famous British lighthouse and indeed one of the most famous lighthouses in the world. The first tower, built of wood, had to be rebuilt one year later and lasted only 4 more years. The third (Rudyerd's Tower), was designed by John Rudyerd and built with alternate courses of oak timbers and granite blocks. Remarkably durable, this tower (the first successful open ocean lighthouse in the world) stood from 1709 until it burned in 1755. The fourth tower was a tapered granite and concrete structure built by John Smeaton. A huge advance in civil engineering, it introduced techniques that became standard in lighthouse construction. Completed in 1759, it stood until cracks in the masonry forced its removal in the 1880s. The upper portion of Smeaton's Tower was rebuilt on Plymouth Hoe (see above) but the base of the original remains next to the current tower. A Fresnel lens was installed in Smeaton's Tower in 1845. The present tower, designed by Sir James Douglass, is built with granite blocks that are interlocked both side to side and above and below, giving the tower exceptional strength. Located on a rock that barely breaks the surface of the sea about 25 km (15 mi) south southwest of Plymouth. Accessible only by boat or helicopter. Site and tower closed.

About Douglass's lighthouse

Source: https://www.wikiwand.com/en/Eddystone_Lighthouse

The current, fourth lighthouse was designed by James Douglass (using Robert Stevenson's developments of Smeaton's techniques). This lighthouse is still in use.

Design and building

By July 1878 the new site, on the South Rock was being prepared during the 3¬Ω hours between ebb and flood tide; the foundation stone was laid on 19 August the following year by HRH The Duke of Edinburgh, Master of Trinity House. The supply ship Hercules was based at Oreston, now a suburb of Plymouth; stone was prepared at the Oreston yard and supplied from the works of Messrs Shearer, Smith and Co of Wadebridge. The tower, which is 49 metres (161 ft) high, contains a total of 62,133 cubic feet of granite, weighing 4,668 tons. The last stone was laid on 1 June 1881 and the light was first lit on 18 May 1882.

The lighthouse was topped by a larger than usual lantern storey, 16 ft 6 in (5.03 m) high and 14 ft (4.3 m) wide; the lantern was painted red. It contained a six-sided biform (i.e. two-tier) rotating optic of the first-order, 12 ft 6 in (3.81 m) high and weighing over seven tons. Each of the six sides of the optic was divided into two Fresnel lens panels, which provided the light's characteristic of two flashes every thirty seconds. The optic was manufactured by Chance Brothers of Smethwick and designed by their chief engineer John Hopkinson FRS. At the time the Eddystone's extra-tall (6 ft 3 in (1.91 m)) lenses were the largest in existence; their superior height was achieved through the use of extra-dense flint glass in the upper and lower portions of each panel.

The light had a range of 17 nautical miles (31 km; 20 mi). Illumination was provided by a pair of Douglass-designed six-wick concentric oil burners (one for each tier of the optic). This was said to represent 'the first practical application of superposed lenses of the first order with oil as the illuminating material'. On clear nights, only the lamp in the lower tier of lenses was lit (producing a light of 37,000 candlepower); in poor visibility, however (judged by whether the Plymouth Breakwater light was visible), both lamps were used at full power, to provide a 159,600 candlepower light. Eighteen cisterns in the lower part of the tower were used to store up to 2,660 tons (nine months' worth) of colza oil to fuel the lamps.

In addition to the main light a fixed white light was shone from a room on the eighth storey of the tower (using a pair of Argand lamps and reflectors) in the direction of the hazardous Hand Deeps. The lighthouse was also provided with a pair of large bells, each weighing two tons, by Gillett, Bland & Co., which were suspended from either side of the lantern gallery to serve as a fog signal; they sounded (to match the light characteristic of the lighthouse) twice every thirty seconds in foggy weather, and were struck by the same clockwork mechanism that drove the rotation of the lenses. The mechanism required winding every hour (or every forty minutes, when the bells were in use), 'the weight to be lifted being equal to one ton'; shortly after opening, the lighthouse was equipped with a 0.5 h.p. caloric engine, designed 'for relieving the keepers of the excessive strain of driving the machine when both illuminating apparatus and fog bell are in use'.