drilled by drilling boreholes. Bamboo towers were erected, similar in style to modern-day oil derricks. Bamboo was used for ropes, casing, and derricks since it was salt resistant. Iron wedges were hung from a bamboo cable tool attached to a lever on a platform constructed atop the tower. The derricks required two to three men jumping on and off the lever that moved the iron wedge pounded into the ground to dig a hole deep enough into the ground to hit the brine. Bristle toothbrush: According to the United States Library of Congress website, the Chinese have used the bristle toothbrush since 1498, during the reign of the Hongzhi Emperor (r. 1487–1505) of the Ming Dynasty (1368–1644); it also adds that the toothbrush was not mass-produced until 1780, when they were sold by a William Addis of Clerkenwell, London, England. In accordance with the Library of Congress website, scholar John Bowman also writes that the bristle toothbrush using pig bristles was invented in China during the 1490s. While Bonnie L. Kendall agrees with this, she noted that a predecessor existed in ancient Egypt in the form of a twig that was frayed at the end. Bulkhead partition: The 5th century book Garden of Strange Things by Liu Jingshu mentioned that a ship could allow water to enter the bottom without sinking, while the Song Dynasty author Zhu Yu (fl. 12th century) wrote in his book of 1119 that the hulls of Chinese ships had a bulkhead build; these pieces of literary evidence for bulkhead partitions are confirmed by archaeological evidence of a 24 m (78 ft) long Song Dynasty ship dredged from the waters off the southern coast of China in 1973, the hull of the ship divided into twelve walled compartmental sections built watertight, dated to about 1277. Western writers from Marco Polo (1254–1324), to Niccolò Da Conti (1395–1469), to Benjamin Franklin (1706–1790) commented on bulkhead partitions, which they viewed as an original aspect of Chinese shipbuilding, as Western shipbuilding did not incorporate this hull arrangement until the early 19th century. C Candle clock: Candle clocks have been used in China since at least the 6th century AD. The earliest reference of a candle clock is in a poem by You Jiangu around 520 AD. Cannon: The earliest known depiction of a cannon is a sculpture from the Dazu Rock Carvings in Sichuan dated to 1128, however the earliest