Why see it?

This bizarre fashion for enormously-wide dresses fossilized into a kind of uniform that all the ladies at the Georgian court were required to wear. 

Ludicrously impractical, the dresses were worn over whalebone hoops and weighed down with heavy silver thread.   

Who wore this gorgeous creation?

It is believed to have belonged to Mary, Marchioness of Rockingham, who was married to Charles, 2nd Marquis of Rockingham.  This dress was probably worn by Lady Rockingham when her husband became Prime Minister.