In The Count of Monte Cristo, characters often showed up to the opera after the first act was already finished. The narration says that this was the fashionable thing to do at the time. Why was this, and why did it start?
As a corollary to this when did it customary to prevent people from entering an opera or else forcing them to wait until between acts? Was it based on social status (i.e. a Count could get in half-way but if you're in the cheap seats tough luck?)