It is not our design to enter into an elaborate description of this piece of mechanism, as every student of philosophy, who is well acquainted with the reflection and refraction of rays of light, will understand how an ingenious contrivance produced the results spoken of.  The same principle enters into the arrangement of the camera obscura.  There was an aperture very artfully cut through the wall, and so guarded on the outside as to escape notice; and in this a tube was placed with a set of happily contrived fixtures, by the aid of which the scene without was accurately depicted on the polished surface within.  It was the work of the captain, as Eveline supposed.

As this contrivance was evidently intended to give information of danger from without, it must certainly be connected in some manner with the means of escape; else what was it worth?  Such was the conclusion to which Eveline arrived, as she philosophized upon the matter.  And she reflected further, what other method of escape was there, save a secret medium of communication with the outer world?  None at all, except it be a quiet waiting within the passage she now herself occupied, which she could not bring herself to believe was the case; so she renewed her search for the door of egress.

On minutely examining the mirror, she saw at one side of it a small projection, like a ball of ivory, and pressing hard upon it, a door, of which the mirror itself was a section, sprang a little way open.  She threw it back wide on its hinges, and holding her lamp in the opening, saw at her feet a flight of stairs leading down into the gloom below.  A damp current of air came up from this subterranean cavity, and its clammy coldness sent a chill almost of horror through the frame of the agitated girl.  One less resolute than herself would have shrunk at the idea of exploring so dismal a looking place; but not so she.  Summoning all her energy, she boldly descended the steps, which had evidently been cut out by the hands of man, and soon found herself at the bottom of the course.  In front of her, all was solid earth and rock; but on turning to the right she discovered an opening, following which it was but a little while till she saw light ahead, and a few more steps brought her to the margin of the stream, along the bank of which was the path to the cave.  That path, then, was immediately above her!  And here she was with the wide world before her!  How her heart bounded!

Her first thought was to fly immediately; but prudence dictated a cautious survey of the place before venturing her all in an attempt at flight.