Symbolism, Imagery, Allegory
Technology works as the exact opposite of magic in the book, and represents intelligence, self-reliance, and general capability. Hank solves most problems with technology, including the pumps he uses to clear the holy fountain, the lightning rod that destroys Merlin's castle, and the bicycles that the knights use to ride to the rescue. It's important to note that technology comes from an American, while magic and superstition belong to the Englishmen. It isn't just symbolic of Hank's brains and ingenuity then, but also lets Twain thumb his nose at the snooty folks across the Atlantic, while pointing out how awesome American ingenuity is.
It grows problematic only at the end, when Hank saves himself and his followers by slaughtering 25,000 knights with electric wire and Gatling guns:
The thirteen gatlings began to vomit death into the fated ten thousand. They halted, they stood their ground a moment against that withering deluge of fire, then they broke, faced about and swept toward the ditch like chaff before a gale. (43.16)
Twain doesn't comment on the sheer slaughter that occurs, but it undoes the good guys by trapping them with an increasingly stinky and disease-ridden mound of corpses. Like a lot of the other symbols in this book, it turns back on itself in the last few chapters, when comedy quickly becomes tragedy.