and appear to uncommon advantage. The picturesque would be spoilt by admitting a fourth.

Chapter 10.

What does Elizabeth Bennet mean in this passage?

I think it would be helpful to look at the work to which Elizabeth is referring, in order to get the joke ;-)

We are all familiar, I am sure, with Henry Austen’s Biographical Notice of his sister, which was published after JA’s death. In it he mentions JA’s fondness for the works of William Gilpin:

At a very early age she was enamored of Gilpin on the Picturesque; and she seldom changed her opinions either on books or men

William Gilpin was an influential writer in the 18th century, on traveling in the UK, and is distinguished from others in that in his works he endeavored to teach people “how to look” and appreciate what they saw around them.

Here are his biograhical details to give you some background

In chapter 10,when she sees Mr. Darcy and Miss Bingley, arm in arm, then rudely joined by Mrs. Hurst to exclude her , Elizabeth is clearly making an allusion to Gilpin’s comments on grouping figures in the landscape or in pictures, as made in his bookObservations, relative chiefly to picturesque beauty, made in the year 1772, on several parts of England; particularly the mountains an lakes of Cumberland and Westmoreland which was published in two volumes in 1786.

This is a scan of the fontispiece of my copy of the 1808 edition:

Well, to be frank, Elizabeth was being ever so slightly rude( but clever). She was making an allusion to Gilpin's comments on the correct grouping of cows LOL

JA knew this work intimately, it seems to me. She was not above ridiculing Gilpin’s rather pompous style, no mater how “enamored” she might be of him. An example of this is to be found in the very strong but cutting allusion she made to his writing on his birthplace Scaleby Castle in the same book, Observation etc, in her youthful work the “History of England”.

Let's have a look at the relevant passages in his book, pertaining to the grouping of larger cattle.

These two prints are meant to explain the doctrine of grouping larger cattle.

In his notes to the print Gilpin wrote:

But with three, you are almost sure of a good group, except indeed they all stand in the fame attitude, and at equal distances. They generally however combine the most beautifully, when two are united, and the third a little removed.

Four introduces a new difficulty in grouping. Separate they would have a bad effect. Two, and two together would be equally bad. The only way, in which they will group well, is to unite three, as represented in the second of these prints, and to remove the fourth.

and

JA was not the only one who poked fun at Gilpin’s’ style. A book she had also read, Dr Syntax’s Tour in Search of the Picturesque(1810) written by William Combe and illustrated by Thomas Rowlandson did exactly this.

Here is an extract from one of her letters to Cassandra where she makes a direct reference to Dr Syntax:

Give my love to little Cassandra! I hope she found my bed comfortable last night and has not filled it with fleas. I have seen nobody in London yet with such a long chin as Dr. Syntax, nor anybody quite so large as Gogmagoglicus.
Henrietta Street, Wednesday, March 2 (1814)

Note that Rowlandson followed Gilpin’s instructions about grouping cows to the letter ;-)

I'm sure the well-read Darcy understood Elizabeth's allusion( and as even he was affronted by the Superior Sisters rude behaviour, he proably admired Elizabeth's ready wit and intelligence: but as for the Superior Sisters themselves ...Do you think they would ever realise just how they had been picutred by Elizabeth in her imagination?LOL