1831! - Annus Mirabilis The Making of Modern Ballet

Does anything really - fundamentally - change as the ballerina dances through the years or do we just see things a bit differently? I believe that the year 1831 can be truly considered a miraculous year in the development of dance in the theatre - but what happened and why? And was it all of a sudden? Or simply the turning point of developments very long in the making? Are the names we use now for these developments a help or a hindrance? And are the terms used at the time of any utility? 

Or simply 太早说出来!