The first Chinese translation of the last nine books of Euclid's Elements and its source

Books VII to XV of the Elements (Books VII to XIII by Euclid and Books XIV and XV by Hypsicles of Alexandria) were first translated into Chinese by the British missionary Alexander Wylie and the Chinese mathematician Li Shanlan between the years 1852 and 1856. The translation was subsequently published in 1857. Neither of the translators in their prefaces to the translation or in their other writings mentioned the specific original source. Accordingly, historians have pondered this question ever since. Some took a bold guess that its source was Isaac Barrow's English translation. This article provides solid evidence to show that the guess is wrong, and argues that the first English translation of Euclid's Elements of 1570 by Henry Billingsley was the actual source.