The tone of Journey to the Center of the Earth is nuanced and follows a clear developmental arc. This is largely because it’s entirely told in the first person. Its young protagonist writes from an imagined future, so the narrative voice is from the first-person perspective. Axel’s attitude to the events he’s undergoing fluctuates primarily between serious contemplation, dreamy fantasies of success, and nervousness about the dangers and changes ahead.
Initially, the narrator approaches his perilous trip with a certain degree of naivety and self-centeredness. Verne offers readers a viewpoint that reflects Axel’s youth and inexperience. He worries about his fiancée, about his physical safety, and about his uncle’s sanity. However, as the novel unfolds, there's a noticeable shift in tone. The tonal change reflects Axel’s developing maturity, reflecting his growing self-confidence and knowledge of the world. Instead of being anxious, the narrator starts to turn more toward scientific analysis and open-minded curiosity. This mirrors Axel’s building confidence and his wish to make sense of the extraordinary environment he navigates. There are also moments when Axel’s mental state is directly represented in the writing. He isn't universally content and intellectually engaged, by any means. For example, during the frightening lightning storm scene, the novel's diction becomes as disjointed as the narrator’s thoughts and fears are.
By the book's conclusion, the tone has become steadily confident and positive. The narrator speaks as if constantly celebrating the spirit of science and adventure. This does more than just illustrate Axel’s growth into maturity. It communicates the novel's (and the author’s) overarching endorsement of scientific curiosity. In Journey to the Center of the Earth, then, Verne’s tone advocates for intellectual bravery and the willingness to push boundaries. Although the author wasn’t a scientist himself, this novel and many of his other works of speculative fiction reflect a deep commitment to scientific discovery.