When Lever Principle Was Discovered in Ancient China

Lever principle is a basic principle that all kinds of weighing apparatus in ancient time must abide by. It had played an important role in the developing process of traditional metrology. The time when it was known by ancient people cannot be later than that when lever scale with different beams was used. The essential prerequisite for using lever scale is that its maker knew the principle well. The pre-Qin book Mojing is the first in ancient China that described the working characteristic of lever scale theoretically. During the period of Zhao King of the Yan State,people had ever tried to weigh a huge pig in lever. Moreover,there are copper lever scales of the Warring States period (475- 211 BC)existed in unearthed cultural relics today. Considering those factors mentioned above,we might say that the time when lever principle was discovered in ancient China was no later than the Warring States period, which is nearly at the same time with Western countries.