Popular Science Monthly/Volume 1/October 1872/Visual Images in Darkness
|VISUAL IMAGES IN DARKNESS.|
THERE is a chapter in Sir John Herschel's volume of "Lectures on Scientific Subjects" which treats of certain peculiar forms of ocular spectra, under the above title.
The spectra here alluded to—those which present themselves to us, independently of the will, in darkness or when the eyes are closed—are familiar to us all; but it appears to me that the subject has certain bearings which have been hitherto overlooked, and which merit a passing notice.
In the first place, I must beg permission to quote Sir John's own words respecting the most frequently-occurring forms—those possessing perfect geometrical regularity:
"I find them," he says, "to be formed in darkness, and, if the darkness be complete, equally with open or closed eyes.
"The forms are not modified by slight pressure on the retina, but their degree of visibility is much and capriciously varied by that cause. They are very frequent; in the majority of instances, the pattern presented is that of lattice-work, the longer axis of the rhombs being vertical. Sometimes, however, the larger axes are horizontal. The lines are sometimes dark on a light ground, and sometimes the reverse. Occasionally at their intersection appears a small, close, and apparently complete piece of pattern work, but always too indistinct to be clearly made out.
"Occasionally the latticed pattern is replaced by a rectangular one, and within the rectangles occurs in some cases a filling-up of a smaller lattice-pattern or of a lozenge of filigree-work, of which it is impossible to seize the precise form, but which is evidently the same in all the rectangles.
"Occasionally, too, but much more rarely, complex and colored patterns like those of a carpet appear, but not of any carpet distinctly remembered or lately seen; and in two or three instances in which this has been the case the pattern has not remained constant, but has kept changing from instant to instant, hardly giving time to apprehend its symmetry and regularity, before being replaced by another; that other, however, not being a sudden transition to something totally different, but rather a variation on the former."
Thus far I have spoken of rectilinear forms; with myself, however, curvilinear forms more frequently present themselves. These so closely resemble the spectra which Sir John describes as having presented themselves to him when under anaesthetic influence, that I again quote his words:
"The indication," he says, "by which I knew it" (the chloroform) "had taken effect consisted of a kind of dazzles, immediately followed by the appearance of a very beautiful and perfectly symmetrical Turk's-cap pattern formed by the intersection of a great many circles outside and tangent to a central one. It lasted long enough for me to contemplate it so as to seize the full impression of its perfect regularity, and to be aware of its consisting of exceedingly delicate lines, which seemed, however, to be not single but close assemblages of colored lines not unlike the delicate fringes formed along the shadows of objects by minute pencils of light. The whole exhibition lasted, so far as I could judge, hardly more than a few seconds."
On the administration of chloroform a second time, after an interval of many months, "the Turk's-cap pattern again presented itself on the first impression, which I watched with some curiosity; but it was not quite so complete as, nor was it identical with the former. In the intersections of the circles with each other I could perceive small lozenge-shaped forms or minute patterns, but not clearly enough to make them well out. On both these occasions the colors were lively and conspicuous. . . . Since that time circular forms have presented themselves, spontaneously, of the shadowy and obscure class. On one occasion circular were combined with straight lines, forming a series of semicircular arches, supported by, or, rather, prolonged beneath into, vertical columns, while another series of arches and uprights, darker than the general ground, appeared, intersecting the former, so as to have the dark uprights just intermediate between the bright ones of the first set. On the second occasion the pattern consisted of a very slender and delicate hoop, surrounded with a set of circles of the same size, as tangents to the centre circle and to one another. On the third occasion the whole visual area was covered with separate circles, each having within it a four-sided pattern of concave circular arcs. All these phenomena were much fainter than in the chloroform exhibition."
The accuracy of these descriptions will be readily admitted, as far as my own observations have enabled me to judge. I am, however, disposed to believe that the forms under which the spectra present themselves vary persistently in different individuals to a considerable extent.
A question now naturally arises: What are these spectra, and how are they formed?
An eminent scientific authority has suggested to me that they are possibly referable to that obscure mental process which Dr. Carpenter has termed unconscious cerebration. (See "Human Physiology.") But, allowing this to be the case, the questions put by Sir John Herschel still remain unanswered:
"Where do the patterns or their prototypes in the intellect originate?
"If it be suggested that a kaleidoscopic power of forming regular patterns, by the combination of casual elements, exists in the sensorium, how is it that we are unconscious of the power—unable to use it voluntarily—only aware of its being exerted at times in a manner in which we have actually no part but as spectators?"
I cannot help thinking that more than one of the most ancient types of symbolism upon which so much learning and ingenuity have been expended in endeavors to invest them with mystical meanings, or to trace their origin in the forms of the organic world, may have been first suggested by these hitherto-unnoticed spectra.
But besides these geometrical forms, there are others, which I must again describe in Sir John Herschel's words:
"I fancy," he writes, "that it is no very uncommon thing for persons in the dark, and with their eyes closed, to see, or seem to see, faces and landscapes. I believe I am as little visionary as most people, but the former case very frequently happens to myself. The faces present themselves voluntarily, are always shadowy and indistinct in outline, for the most part unpleasing, though not hideous, expressive of no violent emotions, and succeeding one another at short intervals of time, as if melting into each other. Sometimes ten or a dozen appear in succession, and have always, on each separate occasion, something of a general resemblance of expression, or some peculiarity of feature common to all, though very various in individual aspect and physiognomy. Landscapes present themselves much more rarely, but more distinctly, and, on the few occasions I remember, have been highly picturesque and pleasing, with a certain, but very limited power of varying them by an effort of will, which is not the case with the other sort of impressions. Of course," he adds, "I am now speaking of waking impressions, in perfect health, and under no sort of excitement."
There is, of course, as Sir John Herschel observes, one marked distinction between these spectra and the abstract forms referred to at the beginning of this paper: "The human features have nothing abstract in their form, and they are so intimately connected with our mental impressions that the associative principle may easily find, in casual and irregular patches of darkness caused by slight local pressure on the retina, the physiognomic exponent of our mental state. Even landscape scenery, to one habitually moved by the aspects of Nature in association with feeling, may be considered in the same predicament. We all know," he adds, "how easy it is to imagine faces in casual blots, and to fancy pictures in the fire."
However this may be, I am inclined to think that we have here an, as yet, unacknowledged source of many widely-prevailing conceptions of the "world unseen."
If we are to believe with the eminent German mythologist, Dr. Swartz, that there was a time, strange as it may now appear, "when men had not yet learned to suspect any collusion between their eyes and their fancy;" when fast-scudding clouds were flying horses or fleeting swans; when the rolling masses of vapor in the west, as the day declined, were mountains in the far-off cloud-land—not in the sense of poetic figments, but in sober reality—we can scarcely doubt but that the shadowy resemblances of which we have just spoken would be, in like manner, regarded as real existences.
Even stopping short of this extreme view of the case, I think it is difficult to suggest a more probable origin for that universally-prevailing belief, which peoples the darkness with shadowy forms—the thousand fleeting shapes which
"Make night hideous;"
or of that equally wide-spread faith in the existence of hidden realms of enchantment, of which we have types in the mystic caves of Eastern story, and the glimpses of fairy-land in our own folk-lore.
It will be observed that the phenomena above described present themselves in health, and in the absence of all excitement.
Where these two conditions are wanting, both voluntary and involuntary spectra present themselves with greater frequency and distinctness. Medical works abound in such cases, and Sir J. Herschel gives several suggestive examples from his own personal experience, which space forbids my quoting here.
There is, however, one point to which he refers which should not be overlooked. Whatever views we may be disposed to entertain respecting either the mental conditions in which these phenomena originate, or the external agencies by which these conditions are produced or modified, there is reason to believe that the appearances themselves are really formed upon the retina of the eye, and thus they may be fairly placed in the category of "things actually seen."—Science Gossip.