Which 19th-century novel features Captain Nemo and the Nautilus?

Twenty Thousand Leagues Under the Seas, published in 1870 - and the title measures distance travelled, not depth. Twenty thousand leagues is about 80,000 kilometres, roughly twice round the world; a league of depth would put the submarine well through the crust.

Verne got a great deal right by extrapolating carefully rather than guessing. Practical submarines, electric propulsion, diving suits with self-contained air, and the sheer scale of the deep-sea environment all arrived later. He also got things wrong in instructive ways, particularly the biology - he has divers walking comfortably at depths that would kill them.

Nemo is the more interesting invention. Verne wrote him as a Polish nobleman whose family had been destroyed by Russia, and his publisher objected because Russia was a valuable market - so the backstory was removed and left blank, which made the character far stranger and more memorable. In a later novel Verne made him an Indian prince dispossessed by the British Empire, which fits his rage at imperial navies rather better. Nemo means nobody in Latin, which is the name Odysseus gives the Cyclops.