Let's take a look at what's going on with Thornton. He's taken by surprise the very moment Margaret enters the room: first, because she isn't Mr. Hale (or a little girl) and second, because she is "a young lady of a different type to most of those he was in the habit of seeing."
What is is that sets Margaret apart from the rest? What is he seeing? She has a self-composed natural dignity, a straight-forward unabashed manner, a simple yet elegant costume, and a beautiful countenance. All this he notices in a few seconds.
Then Margaret speaks: "Mr. Thornton, I believe."
And he can't even formulate a response! "The ready words would not come."
He's standing there, staring at her, already tongue-tied. Can you picture this? I hope he at least remembered it's not polite to leave your mouth hanging open!
Since Thornton seems mute, Margaret takes command of the social situation. Explaining that her father will return soon, she asks Thornton to sit. Here's how Thornton -- venerated Milton magistrate and master over hundreds of men -- reacts:
"Mr Thornton was in habits of authority himself, but she seemed to assume some kind of rule over him at once. He had been getting impatient at the loss of his time on a market-day, the moment before she appeared, but now he calmly took a seat at her bidding."
He manages to utter something about going to find her father. And as she replies about the house her family intends to take, Thornton suddenly feels that the place he approved for the Hales in Crampton will not be good enough "now that he [sees] Margaret with her superb ways of moving and looking."
Okay, so now she at least got him to sit down, but I don't think he's been able to take his eyes off of her. I mean, he's known her for less than two minutes and he's internally raving about "her superb ways of moving and looking?!" I think the man has been gobsmacked.
Margaret, however, has no clue she's causing any internal combustion. But as she takes off her shawl and takes a seat in front of him, Thornton is drinking in every detail of her feminine appearance:
"... her full beauty met his eye; her round white flexile throat rising out of the full, yet lithe figure; her lips, moving so slightly as she spoke, not breaking the cold serene look of her face with any variation from the one lovely curve; her eyes, with their soft gloom, meeting his with quiet maiden freedom."
There's only so much that Gaskell can describe while staying within the confines of Victorian propriety, but with these well-chosen words I am imagining Thornton's gaze roving over Margaret's body in a way that is unmistakably sensual. He's watching her lips as she speaks and noticing her bare neck? Whew! But that's not all. If his eyes are sweeping up to notice her throat "rising out of the full, yet lithe figure," I think we can assume he hasn't missed surveying the ample curves found below the neck. Ahem.
Go ahead and read that passage again and visualize where Thornton's gaze is lingering. The physical attraction is potent.
Yet, it's not merely physical attraction that enchants him. The beauty he sees in her is tied to the qualities she exudes: self-possessed dignity, serene freedom, natural grace, gentle frankness, unshrinking self-confidence and strength. He seems to discern the essence of Margaret Hale in one short occasion. She's a rather amazing blend of both masculine and feminine natures. And Thornton is drawn to her expression of these qualities, so many of which he himself possesses and venerates.
So how does this unexpected powerful attraction to a woman impact Thornton? He's thoroughly discombobulated. He can't formulate full sentences in response to Margaret's attempt to make conversation. He's irritated and mortified to recognize that "while he looked upon her with an admiration he could not repress, she looked upon him with proud indifference." He feels inadequate as a match for her and feels resentment rise at the thought that she must look down on him. And when it's time for him to leave, her respectful bow to him makes him feel "more awkward and self-conscious in every limb than he had ever done in all his life before."
I love that he exits that scene almost literally off-balance! Even walking is a new sensation when Margaret is in the room.
Can we, then, certify that Thornton has fallen in love at first sight? Well, let's see if we can tic the boxes on a few common elements of what falling in love often looks and feels like:
- Undeniable, strong physical attraction. √
- Vaulted admiration of character/qualities. √
- Feeling awkward, self-conscious, and unworthy. √
- Bumbling, stuttering like an idiot. √
Whether or not his feelings can actually can be called "love" after such a brief encounter, Thornton has all the symptoms of falling for Margaret at their very first encounter.
And it only gets worse from him as the story continues. Poor man.