Author's Note 38

"When under special conditions we cannot form a fair idea of distance, when we can only judge things by the size of the angle or rather of the image formed in our eyes, we cannot avoid being deceived as to the size of these objects. Every one knows by experience how when we are travelling at night we take a bush near at hand for a great tree at a distance, and vice versa. In the same way, if the objects were of a shape unknown to us, so that we could not tell their size in that way, we should be equally mistaken with regard to it. If a fly flew quickly past a few inches from our eyes, we should think it was a distant bird; a horse standing still at a distance from us in the midst of open country, in a position somewhat like that of a sheep, would be taken for a large sheep, so long as we did not perceive that it was a horse; but as soon as we recognise what it is, it seems as large as a horse, and we at once correct our former judgment.

"Whenever one finds oneself in unknown places at night where we cannot judge of distance, and where we cannot recognise objects by their shape on account of the darkness, we are in constant danger of forming mistaken judgments as to the objects which present themselves to our notice. Hence that terror, that kind of inward fear experienced by most people on dark nights. This is foundation for the supposed appearances of spectres, or gigantic and terrible forms which so many people profess to have seen. They are generally told that they imagined these things, yet they may really have seen them, and it is quite possible they really saw what they say they did see; for it will always be the case that when we can only estimate the size of an object by the angle it forms in the eye, that object will swell and grow as we approach it; and if the spectator thought it several feet high when it was thirty or forty feet away, it will seem very large indeed when it is a few feet off; this must indeed astonish and alarm the spectator until he touches it and perceives what it is, for as soon as he perceives what it is, the object which seemed so gigantic will suddenly shrink and assume its real size, but if we run away or are afraid to approach, we shall certainly form no other idea of the thing than the image formed in the eye, and we shall have really seen a gigantic figure of alarming size and shape. There is, therefore, a natural ground for the tendency to see ghosts, and these appearances are not merely the creation of the imagination, as the men of science would have us think."-Buffon, Nat. Hist.

In the text I have tried to show that they are always partly the creation of the imagination, and with regard to the cause explained in this quotation, it is clear that the habit of walking by night should teach us to distinguish those appearances which similarity of form and diversity of distance lend to the objects seen in the dark. For if the air is light enough for us to see the outlines there must be more air between us and them when they are further off, so that we ought to see them less distinctly when further off, which should be enough, when we are used to it, to prevent the error described by M. Buffon. Whichever explanation you prefer, my mode of procedure is still efficacious, and experience entirely confirms it.