AD 1088: The Dream Pool Essays is published by the Chinese polymath scientist and statesman Shen Kuo. His book represents the earliest known writing about the magnetic compass, movable type printing, experimentation with the camera obscura only decades after Hasan ibn al-Haytham, which includes many different fields of study in essay and encyclopedic form, including geology, astronomy, archaeology, mathematics, pharmacology, magnetism, geography, optics, hydraulics, economics, military strategy, philosophy, etc. Some of Shen's most advanced theories include geomorphology and climate variability, while he improves Chinese astronomy, by fixing the position of the pole star and correcting the lunar error, by plotting its orbital course every night for a continuum of five years. Shen's book is also the first to describe the drydock in China – and discusses the advantages of the recent invention of the canal pound lock, over the old flash lock.