The chamber lock, with two gates, is invented in the Song Dynasty at the end of the 10th century. In 983, a civil servant named Chiao Wei-Yo is in charge of transport in the Huai region. At this time barges were transferred from the canal to the Huai, at the northern extremity of the Shangyang traverse, by dragging them on an inclined ramp. This operation often damaged the heavily-loaded barges and their cargo. To remedy this difficulty, Chiao Wei-Yo conceived the concept of the chamber lock, the very first such device in the history of man:
“Chiao Wei-Ho therefore ordered the construction of two gates at the third dam along the west river. The distance between these two gates was a little more than 50 paces (75 m) and the entire space was covered with a large roof. [….] When the gates were closed, water accumulated like the tide until the desired level was attained, then, when the right moment arrived, it was allowed to flow out.”[430]
Additional evidence of the appearance of the chamber lock comes from the magic canal, linking the basins of the Yangtze and the Xi to the south. Joseph Needham notes that up until the 9th century, written accounts mention 18 single gates on this canal, and that from the year 1178 the number increases to 36. He interprets this doubling as the replacement of the single-gate flush locks by chamber locks with two gates. A later account dating from the 16th century also suggests the existence of chamber locks on this canal:
“On the Ling Chhh (Lingqu — magic canal) north to south there are 32 lock-gates, i. e. from the Li to the Thung-Ku Shui. From east to west, entering Yung-fu, there are 6. In the winter (the canal) dries up and one cannot pass through. But when I made the passage through these lock — gates there was plenty of water, and under the moonlight they looked like steps leading up to some high platform, or like tiers of walls and terraces coming down one behind another from the sky.”[431]
The chamber lock is a Chinese invention that does not appear in Europe until the 14th century. In China itself this invention will have a somewhat murky future, since, as we will see, the old principle of the flush lock will remain in broad use on the Grand Canal for some time to come.
