78-139

Chinese mathematician and astronomer who developed the world's first seismoscope, as well as one of the earliest rotating globes. His seismoscope, an ingenious invention that he unveiled in 132, consisted of a cylinder surrounded by dragons with frogs beneath. When the earth shook, a ball would drop from a dragon's mouth into that of a frog, making a noise. Zhang Heng also produced a corrected calendar in 123, and discussed cosmology in several texts. He provided a figure of √10 for π, which at 3.162 was only correct to one decimal place.