A POPULAR AND SCIENTIFIC DESCRIPTION.
It is a curious fact that, in this age of scientific research, the absurd follies of spiritualism should find an increase of supporters; but mental epidemics seem at certain seasons to affect our minds, and one of the oldest of these moral afflictions—witchcraft—is once more prevalent in this nineteenth century, under the contemptible forms of spirit-rapping and table-turning. The modern professor of these impostures, like his predecessors in all such disreputable arts, is bent only on raising the contents of the pockets of the most gullible portion of humanity, and not the spirits of the departed, over which, as he well knows, notwithstanding his profane assumption, he can have no power.
One thing we hope in some measure to further in the following pages, is the extinction of the superstitious belief that apparitions are actual spirits, by showing some of the many ways in which our senses may be deceived, and that, in fact, no so-called ghost has ever appeared, without its being referable either to mental or physiological deception, or, in those instances where several persons have seen a spectre at the same time, to natural objects, as in the case mentioned by Dr. Abercrombie, in his work on “The Intellectual Powers:”—“A whole ship’s company were thrown into the utmost consternation, by the apparition of a cook who had died a few days before. He was distinctly seen walking ahead of the ship, with a peculiar gait, by which he was distinguished when alive, from having one of his legs shorter than the other. On steering the ship toward the object, it was found to be a piece of floating wreck.”
A ghost, according to the general descriptions of those who fancy they have been favoured with a sight of one, appears to be of a pale phosphorescent white, or bluish white colour; usually indistinct, and so transparent that objects are easily seen through it. When moving, it glides in a peculiar manner, the legs not being necessary to its locomotion.
All the senses are more or less subject to deception, but the eye is pre-eminently so; especially in the case of individuals who are in ill health, because the sensibility of the retina is then generally much exalted, as is also the imagination.
We may divide the illusions to which the sense of sight is liable into four kinds. First, mental, or those arising in the brain itself, and only referred to the eye. Second, those produced by the structure of the eye. Third, those arising from the impressions of outward objects on the retina. Fourth, those produced by various combinations of the foregoing. It is only the second and third we shall have occasion to touch upon. But before we can well understand their nature, it will be necessary to get a slight knowledge of the structure of the eye, and some idea respecting the nature of light.
Fig. 1.
With perhaps the exception of the ear, the eye is the most wonderful example of the infinite skill of the Creator. A more exquisite piece of mechanism it is impossible for the human mind to conceive. The annexed diagram ([Fig. 1]) of a horizontal section of this organ will give a better idea of its general structure than whole pages of letter-press. It will be seen to consist of a globe of three envelopes or coats, which are kept distended by three transparent humours or lenses: the aqueous (e), the crystalline (f), and the vitreous (g). The outer coat (a) is dense, white, and fibrous. In front of the eye it gives place to a perfectly transparent one, called the cornea (d). The next coat, the choroid (b), is vascular, very black on its internal surface, in order that light falling on it through the pupil (h) may not be reflected. The pupil is an opening through a diaphragm which is called the iris (i), from its colour varying in different individuals. It has the power of expanding and contracting the pupil, for the purpose of regulating the supply of light to the retina (c), or third and last coat which lies immediately on the choroid. It is transparent, very complex, and the only part of the eye we shall carefully consider. The following diagram ([Fig. 2]) represents a section of it magnified 250 diameters, a is called the limitary membrane, and forms its innermost surface, or that which is next the vitreous humour; b consists of the layer of optic nerve fibers; c is a layer of grey nerve cells; d, two layers in which the principal retinal blood-vessels are spread out; e, two layers of granular matter; f, Jacob’s membrane, or layer of rods and cones. Fig. 3 will give some idea of the supposed connexion between these various parts, the same letters referring to the same parts as in [Fig. 2.]