De onde vem a luz na Viagem de Júlio Verne ao Centro da Terra?

A maioria das fontes de luz é bastante mundana:

• Eles partem com tochas, embora raramente os usem com medo de causar uma explosão (ênfase minha):

  My uncle had been hard at work all the afternoon. The garden was full of ropes, rope ladders, torches, gourds, iron clamps, crowbars, alpenstocks, and pickaxes—enough to load ten men.

  ^{A Journey to the Center of the Earth Chapter 4: "We Start on the Journey"}

• Durante grande parte da jornada, os viajantes carregam bobinas de Ruhmkorff :

  All our industry and ability were devoted to packing every object in the most advantageous manner—the instruments on one side, the arms on the other, the tools here and the provisions there. There were, in fact, four distinct groups.

  The instruments were of course of the best manufacture:

  [...]

  6. Two Ruhmkorff coils, which, by means of a current of electricity, would ensure us a very excellent, easily carried, and certain means of obtaining light.

  ^{A Journey to the Center of the Earth Chapter 8: "The Eider-Down Hunter — Off At Last"}

  Harry quebra uma dessas bobinas no Capítulo 23, quando ele cai. O outro está quebrado durante a fuga do Mar Central.

• Depois de escapar do mar Central, Hans consegue acender um fogo nos restos de uma das bobinas de Ruhmkorff:

  The clever and patient hunter had succeeded in lighting the lantern; and though, in the keen and thorough draft, the flame flickered and vacillated and was nearly put out, it served partially to dissipate the awful obscurity.

  ^{A Journey to the Center of the Earth Chapter 39: "The Explosion and Its Results"}

  Mas isso rapidamente se apaga; não sobrevive até o final do capítulo.

Mas há alguns exemplos fantásticos:

• A primeira ocorrência de uma fonte de luz inexplicada é no Mar Central (literalmente um mar em uma caverna), que é iluminado por uma fonte desconhecida. Harry especula que a luz é causada por alguns fenômenos eletromagnéticos:

  One thing startled and puzzled me greatly. How was it that I was able to look upon that vast sheet of water instead of being plunged in utter darkness? The vast landscape before me was lit up like day. But there was wanting the dazzling brilliancy, the splendid irradiation of the sun; the pale cold illumination of the moon; the brightness of the stars. The illuminating power in this subterranean region, from its trembling and Rickering character, its clear dry whiteness, the very slight elevation of its temperature, its great superiority to that of the moon, was evidently electric; something in the nature of the aurora borealis, only that its phenomena were constant, and able to light up the whole of the ocean cavern.

  ^{A Journey to the Center of the Earth Chapter 27: "The Central Sea"}

• Algum tipo de gás luminoso ilumina outra câmara:

  The raft took a sudden turn, whirled round, entered another tunnel—this time illumined in a most singular manner. The roof was formed of porous stalactite, through which a moonlit vapor appeared to pass, casting its brilliant light upon our gaunt and haggard figures. The light increased as we advanced, while the roof ascended; until at last, we were once more in a kind of water cavern, the lofty dome of which disappeared in a luminous cloud!

  ^{A Journey to the Center of the Earth Chapter 40: "The Ape Gigans"}