LONDON (AP).- A long-lost Victorian painting that hung in a family’s unlocked New England beach house for half a century could fetch 500,000 pounds ($800,000) when it is sold next month, Christie’s auction house said Tuesday. “The Derby Day” is an early version of one of the era’s most famous pictures — William Powell Frith’s teeming, picaresque image of the crowds at an 1850s horse race, from a rich family in their carriage to gamblers, acrobats and prostitutes. The finished painting hangs in the Tate Britain gallery in London. The 15-by-35 inch (39 centimeter by 91 centimeter) oil-on-canvas sketch being sold by Christie’s is Frith’s first complete version of the scene. Peter Brown, Christie’s director of Victorian pictures, said the rediscovery of the oil sketch was “immensely exciting.” It had been hanging in a modest New England beach house for decades before a friend of the owner suggested it might be worth something.