"Whatever their origin, they [the auroras] show the existence of causes in virtue of whose energy the upper strata of our atmosphere become self-luminous, sometimes in a high degree; for, in northern regions, our travelers have read by their brilliance. But the Aurora is not the only phenomenon which indicates the existence of a power in the matter of our globe to emit light. One fact, that must have been often noticed, forcibly impresses me with the conviction, that here, through what seems common, truths of much import will yet be reached. In the dead of night, when the sky is clear, and one is admiring the brilliancy of the stars, hanging over a perfectly obscured earth, a cloud, well known to observing astronomers, will at times begin to form, and it then spreads with astonishing rapidity over the whole heavens. The light of the stars being thus utterly shut out, one might suppose that surrounding objects would, if possible, become more indistinct: but no! what was formerly invisible can now be clearly seen; not because of lights from the earth being reflected back from the cloud—for very often there are none—but in virtue of the light of the cloud itself, which, however faint, is yet a similitude of the dazzling shell of the Sun."
After mentioning the phosphorescence of the dark hemisphere of Venus and the belief that something similar has been seen on the unillumined surface of our satellite, he continues thus:
"But the circumstance most remarkably corroborative of the mysterious truth to which these indications point, is the appearance of our midnight luminary during a total eclipse. By theory, she ought to disappear utterly from the heavens. She should vanish, and the sky seem as if no Moon were in being; but, on the contrary, and even when she passes the very centre of the Earth's shadow, she seems a huge disc of bronze, in which the chief spots can easily be described by a telescope."
And that, remember, when the moon is in the utter blackness of the earth's shadow. Of course, another explanation has been advanced; but it does not take the professor long to dispose of that.
"It has been put forth in explanation," he says, "that a portion of the rays of the Sun must be reflected by our atmosphere and bent toward the eclipsed disc, from which again they are reflected to the Earth—thus giving the Moon that bronze color; but, the instant the hypothesis is tested by calculation, we discern its utter inefficiency. Nor is there any tenable conclusion save this:—That the matter both of Sun and planets is capable, in certain circumstances whose exact conditions are not known, of evolving the energy we term light."
All this, and more, Rhodes explained to me, succinctly but clearly.
"Oh, we'll find light, Bill," said he.
All the same this subterranean world for which we were bound presented some unpleasant possibilities, in addition, that is, to those concomitant to its being a habitat of demons—and Heaven only knew what besides.
"And then there is the air," I said. "As we descend, it will become denser and denser, until at last we will be able to use these ice-picks on it."
Rhodes, who was removing his creepers, laughed.