Now the latter theory, admissible after all, was unable to survive the researches carried out in the Old and New Worlds. That a private individual had at his disposition a mechanical contrivance of this sort was improbable. When and where could he have had it built, and how could he have kept its construction secret? (1.2.6)
Maybe amazing individual achievement is less believable because we don't want to admit that other men are more capable than we are. Aronnax is less willing to admit his own limitations than most; he's too interested in being a renowned scientist.
Part 1 Chapter 4
I would not have been nearly so astonished to discover the most fabulous and mythological of creatures. That what is extraordinary could have come from the Creator, is easy to believe. But to discover all of a sudden a mysterious human construction of the impossible, to find it before your eyes was enough to unhinge your mind. (1.4.69)
Here, again, Man seems unwilling to admit that other men can create great things. Perhaps it's no wonder that Nemo fled "society" for open water.
Part 1 Chapter 8
Where were we? What strange force was taking us away? I felt, or rather believed I felt, the machine sinking down to the furthest depths of the ocean. Fearful waking nightmares tormented me. I glimpsed a whole world of unknown animals sheltering in mysterious refuges, with the submarine vessel as one of their congeners, living, moving, formidable like them. (1.8.65)
Aronnax himself says that it's easier to believe in an unknown natural creation than an awesome manmade one. Here, he backs up this claim by observing that the Nautilus is so advanced, it's like an animal. We're always afraid of what we don't understand, right?
Part 1 Chapter 23
When I thought that the marvelous electrical agent not only gave movement, heat, and light to the Nautilus, but also protected it into a holy ark which no desecrator could touch without being struck by lightning, my admiration knew no limits; and this went from being direct to the machine back to the engineer who had built it. (1.23.2)
In order to understand how sophisticated the Nautilus is, Aronnax has to put things in supernatural terms. The sub isn't simply advanced, it's holy. Do you think people have a penchant for attributing the mysterious (but perfectly explainable) to the holy or the supernatural?
Part 2 Chapter 4
"Yes, captain, and the Nautilus lent itself marvelously to all this study. Ah, what an intelligent boat it is!"
"Yes, intelligent, audacious, and invulnerable! It fears neither the terrifying storms of the Red Sea, nor its currents, nor even its reefs." (2.4.43-4)
The Nautilus is "intelligent," just like other living creatures. Why do you think Verne blends the boundaries between the natural world and man-made technology in his futuristic novel, 20,000 Leagues Under the Sea?
"Who knows if a second Nautilus will appear in the next 100 years! Progress is slow, Dr Aronnax."
"Agreed," I replied; "your ship is a century ahead of its time, or perhaps several. What a shame that such a secret must die with its inventor!"
Captain Nemo did not reply. (2.4.48-50)
Aronnax is just about right. The first nuclear submarines were built about a hundred years after 20,000 Leagues was written. How does this passage position Captain Nemo as a misunderstood genius, rather than a vengeful killer?
Part 2 Chapter 9
Was I heading for some natural phenomenon that was still unknown to scientists on land? Or even—for the thought did cross my mind—did man perhaps have a part in this blaze? Was some hand fanning the fire? Would I meet companions or friends of Captain Nemo in these deep strata, living as strange an existence as him, and to whom he was paying a visit? Would I find a whole colony of exiles weary of the miseries of earth who had sought independence at the bottom of the ocean—and found it? All these crazy, impossible ideas haunted me. (2.9.37)
Once you've viewed one manmade wonder, it seems like man is capable of a lot more. After Aronnax experiences the Nautilus, his mind begins racing; if this is possible, what else is possible in the world?
Part 2 Chapter 11
"Can it be that all we will have to take with us are the memories of these yet-unseen sight?"
"Would it please you," Captain Nemo asked, "to take back more than memories?"
"What do you mean?"
"I mean that nothing would be easier than to make a photographic record of this submarine region." (2.11.39-42)
Leave it to Nemo to use another bit of new technology to document his own amazing discoveries. And leave it to Aronnax to fret over making his adventures on the Nautilus immortal; it's all in the name of Science… right?
Part 2 Chapter 15
"And how did we run aground?"
"From a whim of nature, not from human error. There were no operational failures. However, we cannot prevent the effects of equilibrium. One can disdain human laws, but not resist natural ones." (2.15.31-2)
There are some things that no amount of technological sophistication can overcome. Like ice floes. And suffocating from asphyxiation. The lesson here, kiddos, is this: when you mess with Nature, Nature messes with you right back. Okay?!