Kaoru Mori has a bit of a Victorian England obsession; she has stacks of pictures and information and references on the period, and it shows in her work. Unfortunately, most of it is easily lost on the rest of us.
To help out, Mori has also published the Emma Victorian Guide, a companion reference to the series. And for those of us not fluent in Japanese, the IIChan Translation Group does their part with "Whisper's Guide to Emma's World." It's a short feature after every episode, and two pages after every volume, explaining references.
For easy searching, I've pulled out the manga-page extras and listed the tidbits explained on each; the anime follows the first part of the manga closely, so the historical notes are the same.
See Crumpets and Corsets for more historical references.
Volume 1 notes 1
The Crystal Palace/Great Exhibition
Coming Out balls
Volume 1 notes 2
The new aristocracy
Maids (general background)
Volume 2 notes 1
Harrods Department Store
Volume 2 notes 2
Maids (lady's maid, parlormaid)
Flower girls, orange girls
Midland and Great Northern Railroads
Hansom Safety Cab
Volume 3 notes 1
The Industrial Revolution
Volume 3 notes 2
Dances (quadrille, polka, waltz)
New money vs. old money
Volume 4 notes 1
Gretna Green (elopements thereto)
The Barber of Seville
Volume 4 notes 2
Debrett's and Burke's (directories)
Volume 5 notes 1
Volume 5 notes 2