Posted 2017/7/27
The most famous sand glass is the "five-gear sand glass" created by Zhan Xiyuan in 1360. The sand drifted from dipper-shaped sand pool to the sand dipper on the side of the first gear to drive the first gear, making different grades of mechanical gears start to revolve. The last grade of gear pulled the middle gear revolving on the level surface. On the axle center of middle gear there was a finger which revolved on the round plate of instrument with marking lines in order to show the time. This method was completely the same with the surface structure of present clock. In addition to that, Zhan Xiyuan skillfully added a mechanic driving equipment to the middle gear to remind the two wood men standing at the five-gear sandglass to give the time signal by hitting the drum. These two wood men would come out automatically to give the time signal by hitting the drum every hour or quarter. This sandglass was free from supportive astronomic instrument and became an independent mechanic clock structure.
