With nothing but her dog Garrick to her name, strong-willed servant Demelza convinced her master, Captain Poldark, to tie the knot after just one night of passion in the popular new BBC series. But research shows that marriage in the 18th century was actually a mercenary affair in the vast majority of cases which saw many men marry to get their hands on a woman's wealth. Anne Laurence, a historian with Open University, has found that pragmatic marriages made for the preservation or the transfer of wealth became more important during the Poldark era. Her study is based on around 400 marriage announcements in London newspapers when it was common to refer to a bride's wealth, according to The Observer. Scroll down for video . Strong-willed servant Demelza convinced her master, Captain Poldark, to tie the knot after just one night of passion in the popular new BBC series . The fortunes of the brides were routinely given either in thousands of pounds or described as 'large', 'ample', 'considerable' or 'handsome'. In almost two thirds of the announcements studied, the bride's fortune, ranged from £1,000 to more than £20,000. But the wealth of the grooms was rarely mentioned. Ms Laurence said: 'Mercenary marriages became the subject of much criticism, but it would seem that the zeitgeist was against the moralists. 'Western sensibilities react against the idea that marriage might be for reasons other than love of a partner and a desire to spend the rest of one's life with them. But research shows that marriage in the 18th century was actually a mercenary affair in the vast majority of cases, pictured is Aidan Turner as Captain Poldark and  Eleanor Tomlinson as Demelza . The wealth of the grooms was rarely, if ever, mentioned in the 400 marriage announcements studied . 'We recognise no one has to get married to survive. At the same time, the very rich make prenuptial agreements and ever-larger divorce settlements make the news weekly. 'The preservation of a fortune concentrates the mind on pragmatic considerations.' She gave an example of one of the marriage announcement's which said: 'On Tuesday last Gilbert Burton, Esq; eldest son to George Burton, Esq; was married at Foot's Cray near Eltham in Kent, to Miss Craddock, only daughter to Mr Craddock, late an eminent goldsmith in Lombard Street, a beautiful young lady with a fortune of £10,000.' Her study is to be presented at the annual conference of the Economic History Society. A guide was published in 1742 to help men locate wealthy widows and spinsters. More than 400 wealthy woman were listed in 'A Master Key to the Rich Ladies Treasury: the Widower and Batchelor's Directory' including their reputed fortune and  stock market investments. The anonymous author cast his net wide: several of the women were in their 70s and 80s.
Study has revealed that marriage in the 18th century was  a mercenary affair . Historian Anne Laurence studied 400 announcements in London papers . Brides' fortunes were described as  'ample', 'considerable' or 'handsome'
But the wealth of the grooms were rarely mentioned in the publications .