In fine, in all such marvels, supposing even that there is no imposture, there must be a human being like ourselves by whom, or through whom, the effects presented to human beings are produced.  It is so with the now familiar phenomena of mesmerism or electro-biology; the mind of the person operated on is affected through a material living agent.  Nor, supposing it true that a mesmerized patient can respond to the will or passes of a mesmerizer a hundred miles distant, is the response less occasioned by a material being; it may be through a material fluid—­call it Electric, call it Odic, call it what you will—­which has the power of traversing space and passing obstacles, that the material effect is communicated from one to the other.  Hence, all that I had hitherto witnessed, or expected to witness, in this strange house, I believed to be occasioned through some agency or medium as mortal as myself; and this idea necessarily prevented the awe with which those who regard as supernatural things that are not within the ordinary operations of Nature, might have been impressed by the adventures of that memorable night.

As, then, it was my conjecture that all that was presented, or would be presented to my senses, must originate in some human being gifted by constitution with the power so to present them, and having some motive so to do, I felt an interest in my theory which, in its way, was rather philosophical than superstitious.  And I can sincerely say that I was in as tranquil a temper for observation as any practical experimentalist could be in awaiting the effects of some rare, though perhaps perilous, chemical combination.  Of course, the more I kept my mind detached from fancy, the more the temper fitted for observation would be obtained; and I therefore riveted eye and thought on the strong daylight sense in the page of my Macaulay.

I now became aware that something interposed between the page and the light,—­the page was overshadowed.  I looked up, and I saw what I shall find it very difficult, perhaps impossible, to describe.

It was a Darkness shaping itself forth from the air in very undefined outline.  I cannot say it was of a human form, and yet it had more resemblance to a human form, or rather shadow, than to anything else.  As it stood, wholly apart and distinct from the air and the light around it, its dimensions seemed gigantic, the summit nearly touching the ceiling.  While I gazed, a feeling of intense cold seized me.  An iceberg before me could not more have chilled me; nor could the cold of an iceberg have been more purely physical.  I feel convinced that it was not the cold caused by fear.  As I continued to gaze, I thought—­but this I cannot say with precision—­that I distinguished two eyes looking down on me from the height.  One moment I fancied that I distinguished them clearly, the next they seemed gone; but still two rays of a pale-blue light frequently shot through the darkness, as from the height on which I half believed, half doubted, that I had encountered the eyes.