If everybody about here was so honestly and sincerely afraid of Merlin's pretended magic as Clarence was, certainly a superior man like me ought to be shrewd enough to contrive some way to take advantage of such a state of things. (5.3)
Careful, Hank—you're using the very thing you want to destroy… Oh, okay, they're gonna burn you at the stake, so we'll forgive you.
"Banish this calamity, spare the sun!" (6.6)
Arthur is pretty rattled by the eclipse that Hank is passing off as magic. This moment also puts Hank in a bind: he's making use of the very fear that he wants to destroy, which may be one of the things that leads to his downfall. He has to perpetrate belief in the supernatural if he wants to end it, a bind that's bound to create problems down the road.
Those multitudes presently began to agitate for another miracle. (7.4)
The pattern gets set pretty quickly for Hank. He needs to produce "magic" to keep the people in line, which further feeds into the fact that he's a wizard rather than an engineer. It takes the whole book for him to even drop the pretense of magic, and in the end, he still can't undo it.
The castle was enchanted to me, not to her. (20.6)
Rationalization reigns supreme as Sandy has a ready explanation for why the pigs still aren't pigs—belief in the supernatural can't be argued away easily because someone will always have an explanation. Hank has to make deep and abiding changes in the way the society thinks.
If I also would be sane—to Sandy—I must keep my superstitions about unenchanted and unmiraculous locomotives, balloons, and telephones, to myself. (21.2)
Ironic twist here: Sandy thinks Hank's beliefs in modern technology are superstitious. More importantly, he has to keep quiet about the technological changes he has planned, because people will think he's crazy. Belief in science = nuthatch. Belief in ogres and magic? That just might put you in the king's good graces.
If he had stepped in there and used his eyes, instead of his disordered mind, he could have cured the well by natural means, and then turned it into a miracle in the customary way; but no, he was an old numskull, a magician who believed in his own magic; and no magician can thrive who is handicapped with a superstition like that. (22.6)
Hank cuts right to the heart of the matter in explaining Merlin's failures. Could he and Merlin have been allies had Merlin not depended so much on belief in the supernatural? Or were they destined to be enemies, since Hank took Merlin's place as Arthur's chief advisor? It could be that one feeds into the other, since Merlin wouldn't be so afraid of losing his power if he didn't have anything but superstition to peddle.
This distressed the monks and terrified them. They were not used to hearing these awful beings called names, and they did not know what might be the consequence. (24.10)
Again Hank shows us the underlying effects of superstition and belief in the supernatural: fear of speaking out means fear of honest debate, which means that ideas can't flourish and civilization doesn't move forward. Twain knew exactly what the problems were.
Wherever you find a king who can't cure the king's-evil you can be sure that the most valuable superstition that supports his throne—the subject's belief in the divine appointment of his sovereign—has passed away. (26.6)
In the legends, Arthur is appointed divinely and the divine right of kings stood as the law of the land in the Middle Ages. Twain clearly doesn't think much of it.
I was a champion, it was true, but not the champion of the frivolous black arts, I was the champion of hard unsentimental common-sense and reason. (39.4)
Well check you out, Hank the Yank. Aren't you nailing things? Where can our hero go after this… except down?
"Why did you select boys?"
"Because all the others were born in an atmosphere of superstition and reared in it." (42.9-10)
Why does Hank's plan take so long? Because he has to train a whole new generation of people not to be afraid of their own shadow, and that takes time. The tragedy is that it does seem to be working: his young boys here are educated and enlightened, and could have led England to a new golden age free of supernatural beliefs, even if Hank weren't present. It makes the tragedy of the last few chapters all the more painful.