Cleomedes and Wang Chong on the Size of the Earth

Abstract

In the works of Wang Chong and Cleomedes there are coinciding numerical parameters related to the determination of the size of the Earth. In Wang Chong, the numerical data appear partly arbitrary, partly insufficiently substantiated. In the corresponding passage of Cleomedes, the argument pretends to be scientific, but in fact turns out to be internally contradictory and almost illogical. Painstaking reconstruction of the reasonable core in Cleomedes’ account reveals that the numerical parameters given by him go back to a certain early system of Greek astronomy. This system assumed a flat Earth, the movement of the luminaries only above the Earth, the principle of the limited spread of sunlight; it employed the measurement of distances along the meridian based on the proportional change in the length of the shadow and the use of the archaic stadium of 100 single steps. It is about the system of Anaximenes and his followers. In Chinese material, this system is known as the gai tian, and I repeatedly argued its Greek origin. Wang Chong is also an adherent of the gai tian. All this makes it very likely – but still not proven – that the numerical parameters presented by Wang Chong came to him ultimately from Greek sources.