Author: Kenneth L Mitchell explores the life of one of Ireland's greatest ever engineers.

It sounds like the beginning of a distasteful joke; “Did you hear the one about the blind Irishman who built a lighthouse?” But it’s not a joke, instead it’s the true story of an Irishman who overcame some amazing personal obstacles to become one of our greatest ever engineers.

Alexander Mitchell was born on the 13 April 1780 in South William Street, Dublin, the son of an Inspector-General of Army Barracks in Ireland Aged seven, he and his family moved to Pine Hill, Belfast and he attended the prestigious Belfast Academy.

 It was during his time at this school, that his talent for maths first came to attention. Also noticed was his failing eyesight, by age 16 he could no longer read, and in 1802 at the age of 22 he was completely blind.

Undeterred, he borrowed £100 and started up a successful business making bricks in the Ballymacarrett area of Belfast. This enabled him to start building his own houses and he completed around 20 in the city.  

It was during this period that his talent for inventing came to the fore and he fabricated several machines for use in brick-making and the building trade. Described as a tall, strong, active and jovial man, he married his neighbour, Mary Banks (against his mother's wishes), and had five children, some of whom joined the family business and assisted on his various inventions.

His first love was of Irish music and songs; he mastered both the flute and accordion and had a good singing voice.  He even invented his own musical instruments and in 1844 was elected an associate of the Belfast Anacreontic Society.

Belfast has a strong seafaring tradition and no doubt he heard many a tragic story of lives lost at sea. It is also famously built on a mudflat and as a builder he would have witnessed the problems that occurred when building on such strata and set his mind to it. In 1833 he patented his greatest invention; the screw-pile lighthouse, which he described as

A simple means of constructing durable lighthouses in deep water in shifting sands

Inspired by an ordinary bottle corkscrew, this invention enabled lighthouses to be built in shallow water under difficult soil conditions and would prove to be invaluable in getting ships to harbour safely. In addition, they were relatively inexpensive, easy to construct, and comparatively quick to build.

The typical screwpile lighthouse was hexagonal or octagonal in shape consisting of a central pile which was set first and then eight perimeter piles which were screwed into the sea or river bed. 

The piles were screwed 6.5 meters down by men using a capstan keyed onto the pile The screw-like cast-iron flange at the end of the pile was augured into the bottom in order to increase the bearing power and anchoring properties.

Alexander would have to wait five years to see his invention put to use, at the mouth of the Thames with the building of Maplin Sand lighthouse, in 1838.  This was quickly followed by another one at  

A hands-on man despite his disability, he would be seen climbing ladders and scaffolding on his project seemingly impervious to the possibility of falling into the sea and mud beneath.  Actually, he did fall in a couple of times, but these incidents never fazed him and afterwards proceeded with the job in hand as if nothing had happened.  He would personally supervise all his constructions except those in India.

Things did not continue smoothly however, In 1842 he was contracted to build Kish lighthouse in Dublin and disaster struck when his screw piles failed in a gale and the project was abandoned.  Nonetheless, he continued unabated and his first successful Irish lighthouse was built at Belfast Lough in 1844 reflecting in some ways his own life story.  He showed his love for the city by reducing the cost of the construction to the minimum amount he could manage.

Maplin Sand Lighthouse[/caption] In 1847 he used his technology to extend the southern pier in Courtown, Wexford.  In 1851 he laid the foundation for a lighthouse in Cobh, and in 1855 he finished his last two Irish lighthouses at Soldier’s Point, Dundalk.  

These established the success of his invention and soon his screw pile technology were being applied on a broad range of structures and projects as far away as the United States and India. In India his invention was used to construct a viaduct and bridges on the Bombay and Beroda Railway, a system of telegraphs and a pier in Madras. It was in the United States that his invention came to the forefront, firstly with the con

struction of a breakwater at Portland, Oregon, and subsequently over 100 screw-pile lighthouses were erected on the east coast of the United States.  Relentlessly Alexander continued on inventing, most notably been an improved method of mooring ships and this soon was also adopted. In 1848, the Institution of Civil Engineers awarded him the Telford silver medal for his inventions.

Mitchell went on to adapt his technology to propellers and patented the screw propeller in 1854.  This was used on ships, increasing speed, reducing coal consumption and he was awarded a Napoleon medal at the Paris Exhibition for it.

As recently as 2012 his invention was still being used for construction projects for the London Olympics and his screw pile is considered one of the greatest engineering devices of the 19th century. Alexander died on June 25, 1868, at Glen Devis near Belfast and is buried in the old Clifton graveyard, Belfast beside his beloved wife, Mary. 

References

Biography of Mitchell in Belfast Natural History and Philosophical Society Centenary Volume 1821 Brendan O'Donoghue, The Irish County Surveyors 1834-1944 (Dublin: Four Courts Press, 2007) Martin's Belfast Directory for 1841-42 and The Belfast and Province of Ulster Directory for 1852.

Lutenegger, Alan J.(2011). "Historical development of iron screw-pile foundations, 1836-1900". International Journal for the History of Engineering & Technology

Bigger, Francis Joseph  Alexander Mitchell. The Famous Blind Engineer of Belfast  Belfast, 1907

Robb, Colin Johnston, 'The blind lighthouse engineer', 1954, IB 96, 31 Jul 1954, 756 http://www.historyireland.com/18th-19th-century-history/alexander-mitchell-1780-1868-belfasts-blind-engineer/ http://irishscientists.tripod.com/scientists/ALEXANDE.HTM

http://www.buildingsofireland.ie/Surveys/Buildings/BuildingoftheMonth/Archive/Name,1402,en.html http://www.dia.ie/architects/view/3808/MITCHELL-ALEXANDER%5B2%5D http://sources.nli.ie/Record/PS_UR_009397