A new picture by Leonardo da Vinci has been discovered, the National Gallery in London has said. It said experts using infra-red techniques found a drawing under the surface of the Virgin of the Rocks painting which hangs at the gallery. It believes the drawing shows a woman kneeling with one arm stretched out. Experts believe the Italian Renaissance painter was planning a picture of an adoration of the child Christ but abandoned the idea. Leonardo was commissioned to paint the Virgin of the Rocks to decorate an altarpiece in a chapel in Milan in 1483. The artist appears to have painted two versions. One, which now hangs in the Louvre, was probably sold to a private client, says BBC arts correspondent Rebecca Jones.