Thanks for the question! There are numerous differences between Jules Verne’s novel 20,000 Leagues Under the Sea and the 1954 Disney film version. While the original plot of Verne’s story is largely left intact in the film, the film alters several details and characters. Although there are too many differences to outline in detail, I’ve chosen a few to highlight.
One detail that is changed for the film is the modernization of the Nautilus. Verne spends pages of his novel describing the unique battery-system that powers the Nautilus. In the film, Nemo harnesses nuclear power for his submarine. This may seem like a minor detail, but remember that nuclear power had only been harnessed a decade before the release of the film. The early 1950s were a scary time as nuclear weapons proliferated and became more advanced. By transplanting nuclear technology into the film, Nemo’s power is emphasized for his original audience, making his character more potent and dangerous.
Professor Arannax’s interests also vary dramatically between the novel and the film. In the novel, Arannax is introduced to the wonders of the sea by Captain Nemo and, as a marine biologist, loves his time on the sea-floor. He collects specimens and spends large amounts of time recording new species in his journals. In contrast, Professor Arannax of the film is interested largely in discovering the secrets of Nemo’s technology. He repeatedly attempts to persuade Captain Nemo to share his technology with the rest of the world, but Nemo refuses and claims that the world isn’t ready for the power of nuclear fission. These arguments tie back to the Cold War historical context of the film and differ dramatically from the pages of Verne’s novel.
One final difference is the character of Ned Land. In the novel, Land is powerfully built but silent, spending his time brooding and pining for escape. In contrast, in the Disney film, Land is bombastic, violent, and outspoken. Ned Land’s character is played by the legendary actor Kirk Douglas, and his outstanding performance makes Land one of the most memorable characters of the film.
I hope this helps!