Alexander Mitchell, (13 April 1780 – 25 June 1868) was an Irish engineer who from 1802 was blind. He is known as the inventor of the screw-pile lighthouse. After his father's death in his early childhood; Alexander, his mother, sister and brothers rented a cottage a mile from Belfast . From here, Mitchell attended the best classical school in Belfast. He greatly enjoyed his school life, showing a marked taste for mathematics. But his sight always defective, declined rapidly, so that by the age of 16, he could no longer read (Possibly his sight may have been overstrained in his childhood, by lying on the floor of the hall in William street, reading by the dim light that came from the street lamp, through the fanlight over the door). Although this was the case, he seems to have learned a lot in school, as his family constantly came to him for help in geography, history and even spelling.
Mitchell became a brickmaker in Belfast who invented machines used in that trade, and the screw-pile for which he gained some fame. The screw-pile was used for the erection of lighthouses and other structures on mudbanks and shifting sands, and employed with great success all over the world from Portland breakwater to Bombay bridges. It was used for the construction of lighthouses on Maplin Sands in the Thames Estuary (the first light application, in 1838), at Morecambe Bay (the first completed, in 1839), and at Belfast Lough where his lighthouse was finished in July 1844.
In 1848 he was elected member of the Institution of Civil Engineers and received the Telford Medal for a paper on his invention. In May 1851 he moved to Cobh to lay the foundation for that lighthouse; the success of these undertakings led to the use of his invention on the breakwater at Portland, the viaduct and bridges on the Bombay, Baroda and Central India Railway and the whole system of Indian telegraphs.
He was friendly with astronomer John Thomas Romney Robinson, and mathematician George Boole. Even in his poorest and anxious days, Alexander Mitchell was full of good spirit. When friends called, there was always music, as he played the flute and accordion, and sang many Irish songs. He died four years later on 25th June, 1868.
A screw-pile lighthouse is a lighthouse which stands on piles that are screwed into sandy or muddy sea or river bottoms. The first screw-pile lighthouse to begin construction was built by blind Irish engineer Alexander Mitchell. Construction began in 1838 at the mouth of the Thames and was known as the Maplin Sands lighthouse, and first lit in 1841. However, though its construction began later, the Wyre Light in Fleetwood, Lancashire, was the first to be lit (in 1840).
In the United States, several screw-pile lighthouses were constructed in the Chesapeake Bay due to its estuarial soft bottom. North Carolina's sounds and river entrances were also once home to many screw-pile lights. The characteristic design is a 1 1⁄2-storey hexagonal wooden building with dormers and a cupola light room.
Alexander Mitchell invented the screwpile, a major improvement over the standard straightpile construction type. With his son, he patented his wrought-iron screwpile design in England in the 1830s. The Walde Lighthouse in northern France (Pas-de-Calais), established in 1859, was based on Mitchell's design. Although discontinued in 1998 and shorn of its lantern, it is the only remaining screwpile lighthouse in France.
Screwpile lighthouses were relatively inexpensive, easy to construct, and comparatively quick to build. They became especially popular after the Civil War when the Lighthouse Board adopted a policy to replace inside (bays, sounds, and rivers) light vessels with screwpile lighthouses. Most screwpile lighthouses were made with iron piles, though a few were made with wooden piles covered with metal screw sleeves (these sleeves were probably adopted because they were less expensive and easier to insert into the bottom, plus the sleeve protected the wood from marine-boring invertebrates). The typical screwpile lighthouse was hexagonal or octagonal in plan consisting of a central pile which was set first and then the six or eight perimeter piles were screwed in place around it.
Metal screwpiles were used to form the foundation of many lighthouses built on sandy or muddy bottoms. The helicoidal or screw-like cast-iron flange at the end of the metal pile was augured into the bottom increasing the bearing power of the pile as well as its anchoring properties. Yet lighthouses built with these foundations were found to be vulnerable to ice floes. In areas such as the Florida Keys, where the bottom is soft coral rock, diskpile foundation lighthouses were built.
Wrought iron piles were driven through a cast-iron or semi-steel disk which rested on the sea floor until a shoulder on the pile prevented further penetration. The disk diffuses the weight of the tower more evenly over the bottom. In coral reef areas where sand is also prevalent, a cast-steel screw was fitted to the end of the pile to give it more anchoring ability. Cofferdams were used generally in shallow waters where it was not necessary to deeply penetrate the natural bottom. The cofferdam enabled the water inside the dam to be pumped out and the foundation built "in the dry."
SOME INTERESTING POSTS!!!!!
This business leader, with his own vision ventured into new business; became one of the wealthiest & donated 25% of his wealth!!
The near-sighted inventor who left school to support the family, came out with the internal combustion engine !!!