Photograph: Thomas Point Shoal Lighthouse, Chesapeake Bay Maryland.
The problem of erecting a lighthouse on sandbanks and shoals greatly disturbed Alexander Mitchell (1780 – 1868), an Irish brick-maker who ran a successful brick-making business near Belfast.
Belfast has a strong seafaring tradition, and Mitchell had no doubt heard many tragic tales of lives lost at sea and ships grounded on the mudflats. Mitchell decided to do something about it despite having no formal training in engineering, or lighthouse building.
Remarkably, Alexander Mitchell was also blind. Alexander Mitchell was born in 1780 in Dublin, the son of an Inspector-General of Army Barracks in Ireland, a duty that took him all over the country. At the age of seven, Alexander’s family moved to Pine Hill, near Belfast, where he got admission at the prestigious Belfast Academy.
While learning arithmetic, geometry, and trigonometry at school, Alexander discovered his love for mathematics and he excelled at it.
Alexander’s eyesight had always been poor, but it became progressively worse as he became older. At age sixteen, he could no longer read. His family helped him in his studies as young Alexander’s world slowly spiraled into eternal darkness. At twenty-two, he went completely blind.
Mitchell was an outgoing and optimistic man. He married a neighbour’s daughter, against the wishes of his mother, and together they had five children. He also set up a successful brick manufacturing business in the Ballymacarrett area of Belfast that enabled him to buy many property around the city.
Mitchell had an active social life and entertained many guests at his home, including Thomas Romney Robinson, the astronomer, and George Boole, the famous mathematician. He acted so naturally in the presence of others that some people didn’t even know he was blind. He played whist and backgammon with them while an accomplice whispered the throw of the dice or the names of the cards.
Alexander Mitchell ran his brick-making business for 30 years, during which time he made many important contribution to the trade in the shape of several innovative developments to the process.
In 1832, he retired from brick-making, and the following year, at the age of 52, patented the screw pile.
Mitchell’s solution was simple—instead of hammering iron piles straight into the soft mud or clay to make a foundation, they were to be screwed in place. Each pile was to have propeller-like blades attached on one end that would allow them to be twisted into place like a giant corkscrew.