​54Chang Hêng 張衡 (T. 平子). A.D. 78–139. An eminent astronomer and mathematician of the Han dynasty, said by ​some to have been the son of Chang Tao-ling. He graduated as chü jen about A.D. 100, but declined to take office, and gave himself up to scientific studies. The Emperor An Ti, hearing of his fame, summoned him to Court and appointed him Grand Historiographer. The Emperor Shun Ti continued him in this post, and subsequently advanced him to still higher rank. He constructed an armillary sphere, and wrote a treatise on astronomy, entitled 靈憲, besides poetry and miscellaneous treatises.