In China, it was theorized that its water-powered trip hammers and bellows from as early as the Han dynasty (202 BC - 220 AD) were powered by water scoops, but later historians believed that they were powered by waterwheels on the basis that water scoops would not have had the motive force to operate their blast furnace bellows. Evidence of Han vertical waterwheels can be seen in two contemporary funeral ware models depicting water powered trip hammers. The earliest texts to describe the device are the "Jijiupian" dictionary of 40 BC, Yang Xiong's text known as the "Fangyan" of 15 BC, as well as the "Xin Lun" written by Huan Tan about 20 AD. It was also during this time that the engineer Du Shi (c. AD 31) applied the power of waterwheels to piston-bellows in forging cast iron.