This one is officially my favourite of all the dresses in the museum. I just adore the way it flows, it patterns and colours and the overall style. If it were possible to buy them this would be mine! It's definately from the 1800s for sure and has a Jane Austen flair to it, I think.
Now, the pattern is of some leaves/branches/vines which are repeated all over the outerdress. The innerdress or underdress is a plain cream perhaps cotton or silk, the skirt flows wonderfully.
The overdress is actually the bodice and sleeves with a similarly patterned train attached to the middle of it. I just love the way the whole dress seems to flow perfectly and create this Austen/fairytale look.
EDIT - Thinking back and with KingAndrewI's help the 1700's, possibly 1790s about.
From Bath Fashion Museum