房玄龄
Fang Xuanling recorded in the "Book of Jin" chronicle that at around 340 a Jie state Later Zhao's which ruled part of North China had a Chinese scholar Xie Fei (together with Wei Mengbian) serving as a Head of Healing (Medicinal) Department in the Later Zhao State Chancellery, was a mechanical engineer who built a south-pointing chariot (also called "south-pointing carriage"), a directional compass vehicle that apparently did not use magnetic principle, but was operated by use of differential gears (which apply an equal amount of torque to driving wheels rotating at different speeds), or a similar angular differential principle.