From Etidorhpa:
" What you say is not true; we approach daylight, I can see your form."
" Listen to me," he said. " Can not you understand that I have led you
continually down a steep descent, and that for hours there has been no step
upward? With but little exertion you have walked this distance without
becoming wearied, and you could not, without great fatigue, have ascended
for so long a period. You are entering a zone of inner earth light; we are
in the surface, the upper edge of it. Let us hasten on, for when this cavern
darkness is at an end- and I will say we have nearly passed that limit- your
courage will return, and then we will rest."