LONDON.- Known in their times as the nightingales, Elizabeth and Mary Linley were the most beautiful and talked-about young girls in Baths society in the 1770s. From a musical family, they were applauded on the theatre stages of Bath and London, as much as they appeared in the newspapers of the day as society figures. They were portrayed together, in 1772, by Thomas Gainsborough, who was a close friend of their fathers, and their neighbour in Bath. The painter had seen Elizabeth and Mary grow before his eyes and tenderly represented them in their magnificent large canvas known as The Linley Sisters, now at Dulwich Picture Gallery. In the same year as the Dulwich painting was finished by Gainsborough, Elizabeth eloped to France with the young playwright Richard Brinsley Sheridan