Around the beginning of the ethnically Han Ming dynasty (1368–1644), China was leading the world in mathematics as well as science. However, Europe soon caught up to China's scientific and mathematical achievements and surpassed them. Many scholars have speculated about the reason behind China's lag in advancement. A historian named Colin Ronan claims that though there is no one specific answer, there must be a connection between China's urgency for new discoveries being weaker than Europe's and China's inability to capitalize on its early advantages. Ronan believes that China's Confucian bureaucracy and traditions led to China not having a scientific revolution, which led China to have fewer scientists to break the existing orthodoxies, like Galileo Galilei. Despite inventing gunpowder in the 9th century, it was in Europe that the classic handheld firearms, matchlocks, were invented, with evidence of use around the 1480s. China was using the matchlocks by 1540, after the Portuguese brought their matchlocks to Japan in the early 1500s. China during the Ming Dynasty established a bureau to maintain its calendar. The bureau was necessary because the calendars were linked to celestial phenomena and that needs regular maintenance because twelve lunar months have 344 or 355 days, so occasional leap months have to be added in order to maintain 365 days per year. In the early Ming dynasty, urbanization increased as the population grew and as the division of labor grew more complex. Large urban centers, such as Nanjing and Beijing, also contributed to the growth of private industry. In particular, small-scale industries grew up, often specializing in paper, silk, cotton, and porcelain goods. For the most part, however, relatively small urban centers with markets proliferated around the country. Town markets mainly traded food, with some necessary manufactures such as pins or oil. In the 16th century the Ming dynasty flourished over maritime trade with the Portuguese, Spanish and Dutch Empires. The trade brought in a massive amount of silver, which China at the time needed desperately. Prior to China's global trade, its economy ran on a paper money. However, in the 14th century, China's paper money system suffered a crisis, and by the mid-15th century, crashed. The silver imports helped fill the void left by the broken paper money system, which helps explain why the value of silver in China was twice as high as the value of silver in Spain during the end of the 16th