The Oldest and Newest Clock in China In Northern Sung Dynasty (960-1127), Su Song and Han Gonglian, the famous scientists then, created the first accurate and advanced clock in China, that is, the Water-powered Astronomical Clock Tower. It was the symbol of the top of the sciences and technologies of worldwide that time. This machine was first put on the agenda in the year 1086, and seven years later, in the year 1093, it was finally completed....

Topaz Topaz is a hard, transparent mineral. It is a compound of aluminum, silica, and fluorine. Gem topaz is valuable. Jewelers call this variety of the stone precious topaz. The best-known precious topaz gems range in color from rich yellow to light brown or pinkish red. Topaz is one of the hardest gem minerals. In the mineral table of hardness, it has a rating of 8, which means that a knife cannot cut it, and that topaz will scratch...