Glowing Caves of New Zealand

POSTED by Mithrandir: asked May 15 '16 at 17:24

Disclaimer: I haven't read the book yet, but am really curious about this, but am trying to avoid spoilers that give away the whole story. I'm trying to get just an answer to this question without learning too much else. Surely in the center of the earth it would be pitch black? Where does light come from?

POSTED by Jason Baker: answered May 15 '16 at 18:16

Most of the light sources are quite mundane:

They set out with torches, though they rarely use them for fear of causing an explosion (emphasis mine):

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"

For much of their journey, the travellers are carrying Ruhmkorff coils:

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:

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 breaks one of these coils in Chapter 23, when he falls. The other is broken during the escape from the Central Sea.

After escaping the Central Sea, Hans manages to light a fire in the remains of one of the Ruhmkorff coils:

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"

But this quickly goes out; it doesn't survive to the end of the chapter.

But there are a couple of fanciful examples:

The first occurrence of an unexplained light source is in the Central Sea (literally a sea in a cave), which is illuminated by an unknown source. Harry speculates that the light is caused by some electromagnetic phenomena:

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"

Some manner of luminous gas illuminates another chamber:

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"