During a diplomatic mission to the Ming in Beijing in early 1631,[2] Jeong stopped at Dengzhou (now Penglai) on the northern coast of Shandong.
[a] The normal route was overland, but the Koreans were obliged to travel directly across the Yellow Sea owing to the northern war zones created by the initial phases of the Manchu conquest of China.
[4] There, he met with the province's Christian governor under the Ming Ignatius Sun, who introduced him to the Jesuit interpreter João Rodrigues.
[5] He also laded Jeong down with Jesuit texts on astronomy and other sciences[1] including Alenio's Record of Foreign Lands (Korean: 직방외기, Chikpang Oegi);[6][7] a treatise on artillery and its use; and a guide to European customs and manners, as well as works on Christianity.
[8] Nonetheless, the additional material provided to Jeong has still been credited with the full-scale introduction of Western astronomical methods[9] and jurisprudence[6][7] to Korea.