LONDON.- A rare jadeite double-square seal believed to have been an Imperial seal of the Jiaqing Emperor, taken from the Summer Palace during Britains second Opium War with China in 1860, and brought to Britain by Liverpool born medical missionary, William Lockhart, will be sold on May 12th in London at Bonhams auction of fine Chinese Art. The seal which measures under an inch square, is estimated to sell for £40,000 to £60,000. It is being sold with William Lockharts fan which is printed with a map of China on one side and a map of Beijing on the other. The location of Lockharts hospital in Beijing is marked with an X. The seal inscription reads Jiaqing Chen Han (‘Jiaqing Emperor’s Literary and Artistic Work’) and Ji Xia Yi Qing (‘When does one have the leisure to delight the heart?’ Asaph Hyman, a Specialist in Bonhams Chinese Art Department, says: The provenance of the present seal, the presence of t