The waterwheel appeared in Chinese records during the Han. As mentioned by Huan Tan in about 20 AD, they were used to turn gears that lifted iron trip hammers, and were used in pounding, threshing and polishing grain. However, there is no sufficient evidence for the watermill in China until about the 5th century. The Nanyang Commandery Administrator Du Shi (d. 38 AD) created a waterwheel-powered reciprocator that worked the bellows for the smelting of iron. Waterwheels were also used to power chain pumps that lifted water to raised irrigation ditches. The chain pump was first mentioned in China by the philosopher Wang Chong in his 1st-century-AD Balanced Discourse.