Turner's father William Turner (1745–1829) moved to London around 1770 from South Molton, Devon. Joseph Mallord William Turner was born on 23 April 1775 and baptised on 14 May. He was born in Maiden Lane, Covent Garden, in London. His father was a barber and wig maker. His mother, Mary Marshall, came from a family of butchers. A younger sister, Mary Ann, was born in September 1778 but died in August 1783. There are reasons to question the accepted location and birth date for Turner. He sometimes talked of being born in the same year as Napoleon and the Duke of Wellington, which would put his birth date as 1769. His age at death in the General Register Office death index is recorded as 81, which may support a birth year of 1769. However, in the first codicil to his will dated 20 August 1832, he stated that his birthday was 23 April. There has also been doubt about his birthplace, with one claim that he was born at Barnstaple rather than in Maiden Lane or South Molton. Turner's mother showed signs of mental disturbance from 1785 and was admitted to St Luke's Hospital for Lunatics in Old Street in 1799. In 1800 she was moved to Bethlem Hospital, a mental asylum, where she died in 1804. Around 1785 Turner was sent to live with his maternal uncle, Joseph Mallord William Marshall, a butcher in Brentford, a small town on the River Thames west of London, where Turner attended school. The earliest known artistic exercise by Turner comes from this period and consists of simple colourings of engraved plates from Henry Boswell's Picturesque View of the Antiquities of England and Wales. Around 1786 Turner was sent to Margate on the north-east Kent coast, where he produced a series of drawings of the town and surrounding area that foreshadowed his later work. By this time his drawings were being exhibited in his father's shop window and sold for a few shillings. His father proudly told the artist Thomas Stothard that his son was going to be a painter. In 1789 Turner again stayed with his uncle, who had retired to Sunningwell, and a whole sketchbook from this time survives along with a watercolour of Oxford. Turner developed the habit of making pencil sketches on location that he later used as the basis for finished paintings, a working method he continued throughout his career. Many early sketches were architectural studies or perspective exercises, and as a young man he worked for several architects including Thomas Hardwick, James Wyatt and Joseph Bonomi the Elder. By the end of 1789 he had also begun to study under the topographical draughtsman Thomas Malton, who specialised in views of London. Turner learned the basic professional techniques from him, copying and colouring outline prints of British castles and abbeys, and later referred to Malton as his real master. Topography was a thriving industry at the time and provided a way for a young artist to earn money while studying.