When I prepared the core question of lecture 17 (Why did China not colonize the world during the 15th century?) four years ago, Menzies' book "1421, the Year China Discovered America" had just hit the market. It provided some clues that could help to resolve the contradiction between China's technological capabilities and its abstention from colonial conquest.
Over the last few weeks I had another look at Menzies' claims and what others say about them and am no longer so convinced about his book. It contains many dubious statements and relies on evidence provided by people with dubious records; as a result, Menzies has lost much of his credibility. I changed the text of the lecture accordingly and shall install the changed version later today. While I still think that Menzies raises interesting and important questions my lecture notes no longer refer to his theory as a serious contribution to scientific debate. I now leave it to the readers to follow up the question of China's role in 15th century exploration themselves if they want to.
The one thing that has not changed in this discussion is the superiority of Chinese technology over European technology during the 15th century.