In Nanjing, Carter left his companions in order to visit two cousins who were missionaries in Huaiyuan, Anhui province, making the over 200-kilometre (120 mi) journey on foot with a group of Chinese merchants.
[1] In 1921, while reading a book on a train to Shandong, where he was travelling to assist with famine relief, Carter came across a passage about the four great Chinese inventions of the compass, gunpowder, paper and printing, which seized his imagination.
Carter readily took up the suggestion and spent the winter and spring of 1922–3 in Berlin researching archeological material brought from Chinese Turkestan by Albert von Le Coq.
From Berlin, Carter's researches led him to Paris, where he introduced himself to Paul Pelliot of the École française d'Extrême-Orient, the archeologist and sinologist who had collected hundreds of rare manuscripts from the Mogao Caves near Dunhuang in Chinese Turkestan.
Pelliot took an immediate interest in the subject, bringing from his desk drawer a box full of movable type in Chinese characters, hundreds of years older than Gutenberg's, which he had found on a cave floor.
While much of its content has by now been overtaken by subsequent research and archeological discoveries, Carter's book was a ground-breaking contribution to the subject and even now much (such as his chapter on paper) remains relevant.