Popular Science Monthly/Volume 47/August 1895/Art and Eyesight
|ART AND EYESIGHT.|
MEMBER OF THE ROYAL COLLEGE OF SURGEONS OF ENGLAND.
THERE was perhaps no more interesting object at the Columbian Exposition, as an example of a developing appreciation, than the typical Illinois farmer as he stood surprised and bewildered before some of the works of the modern school of painters. His verdict in many instances was doubtless like that of the small boy upon the decorative attempts of an artistic aunt when he said, "It do look awful." Apparently the effect upon at least one such visitor was even more appalling. Perhaps he had been gazing at the various yearnings of the impressionists, or was lost in the labyrinth of color, but at any rate he accosted a bystander in hot haste with "Mister, can you tell me the handiest way to get out of this 'ere place?" If others were not in equal haste to leave the place, they certainly went away questioning seriously what causes had combined to produce some of the conspicuous phases of modern art. Perhaps an explanation can be offered by science. At least, when we examine into the subject we find that the vision of artists is, as a rule, more imperfect than that of other persons. Where this is a not natural defect, artists find it convenient or necessary in their work to make their vision purposely imperfect, and in consequence do not place on canvas what the eye usually sees. Hence a discrepancy between Nature, as seen by the ordinary observer, and its alleged representation by some artists.
The chief imperfection in the vision to which I refer is astigmatism, although either with that, or independently of it, there is usually with artists excessive contraction of the muscle used in focusing the eye—the so-called ciliary muscle. The majority of people have become somewhat familiar with the term astigmatism and its meaning, but, as it involves a rather complicated principle in optics, it may be well to define it here. Technically it might be described as an asymmetry of the eye in which the radius of curvature in one meridian is greater or less than the radius of curvature in another. This definition may be easily understood by a simple illustration. If the transparent portion in the front part of the eye, known as the cornea, were perfectly regular, like the surface of the ordinary sunglass, the rays of light would all tend to converge to a single point; but if the globe were compressed in any one direction—for example, from above downward—then this transparent portion of the eye would not have a regular curvature, but would be somewhat like the top of a Derby hat, held with the long diameter horizontally and the convex surface forward. Practically this is what usually exists in the human eye. As the globe is compressed above and below by the upper and lower lids, it is to a certain extent flattened. This is the usual form of astigmatism, or astigmatism with the rule, as it is called. Other causes tend to make the axes of these two curvatures oblique to each other, or may change their position in various ways, which need not be considered here.
According to the popular idea, the human eye is a perfect instrument, but this, in the vast majority of cases, is not the truth. Nearly every one is astigmatic. Many a person whose eyes are quite imperfect would laugh at the idea if this were told him. He has perhaps always prided himself upon having the best of vision. But the fact is that only a very small per cent of eyes are really free from this unequal curvature which we call astigmatism.
One series of observations made by Dr. Roosa of two hundred eyes, whose owners supposed them to be perfect, and which were apparently perfectly normal, showed that only about one per cent were, beyond question, absolutely perfect, and my own investigation in the same direction would fully corroborate this. If, therefore, a variation from the normal type is so frequent, it is but natural to suppose that artists should have at least their share of astigmatism. But the fact is that among artists astigmatism is not only more frequent, but also that it exists, on the average, in a higher degree, probably, than among any other class of persons.
We can understand the reason for this if for a moment we observe an artist at his work. Having arranged on his palette a variety of pigments, he stands before the easel and applies them to the canvas, but at intervals steps back some few feet in order to get the effect of distance, as he says. It should be noticed that almost without exception the artist when doing this partly closes his eyes, pressing the lids together, making "clingement" as the French call it, because, as he explains, "better effects" are thus obtained. At the same time he tips his head from one side to the other, the reason for which we will consider later. Now, if the eyes of persons with ordinary occupations are changed, as we have seen, by the pressure of the upper and lower lids upon the globe, it is but natural to infer that the same result would follow even in a greater degree with persons whose occupation from morning until night, year in and year out, is such as to cause them to practice to an unusual degree this habit of clingement, or lid pressure upon the cornea. Indeed, this fact has long since attracted the attention of investigators and has been demonstrated and elaborated by Bull, of Paris, and others. Dr. Bull experimented on his own eyes, having them measured exactly by an instrument of wonderful exactness known as the ophthalmometer while he was making this lid pressure. These measurements showed that even this slight momentary contraction of the lids produced a perceptible increase of the unequal curvature of the cornea, and also that a very high degree of astigmatism could with little effort be produced by pressure of the lids.
Very strong a priori reasons, therefore, lead us to expect that the eyes of artists are as a rule more imperfect than those of persons with other occupations. I have taken pains, however, to establish this fact by tests and measurements. The first results of that investigation are given in the American Journal of Ophthalmology for October, 1894, and tests have been made at intervals since then of the vision of artists, record being kept of the variety of work done, style preferred, whether the individual practiced lid pressure habitually or not, and other details of a technical nature. Excluding those on the one hand who were too young in the profession to be really classed as "artists," and on the other hand those whose eyes were practically in a diseased condition, the list thus far includes eighty-four artists, or one hundred and sixty-eight eyes.
Among these, not a single eye was found to be without some astigmatism. This is not surprising, but the degree of astigmatism is significant.
In the series of two hundred eyes already referred to as examined by Dr. Roosa, which had every indication of being absolutely perfect, an exact examination showed that there was, on the average, a degree of astigmatism which technically would be written 0·68 of a dioptre, this dioptre corresponding to a certain weak glass used as the unit of measure.
Among artists, on the other hand, the examination showed that the average was 0·83 of a dioptre, thus being decidedly greater than with persons having other occupations.
It would be interesting to study the degree of this fault as related to the style of the artist, but the limits of this paper do not permit such a long digression. Moreover, this number is small, and there is always danger in generalizing from insufficient data, but I think it fair to say that these facts are sufficient to show the comparatively high degree of the astigmatism of artists, and I am confident that corroborative testimony will not be wanting when this subject is studied by others. Nor is this idea by any means a new one. It is true, exact measurements of the vision of so large a number of painters had not been previously made, but long ago the effects of astigmatism were so conspicuous in some wellknown pictures as to attract attention.
A quarter of a century ago no oculist was more prominent than Prof. Liebreich, of London, or better able than he to speak on questions relating to optics. Unfortunately for that branch of science, he came into a fortune, and, giving up the labors of professional work, devoted himself to the study of painting, thus doubling his equipment for the investigation of such questions as these. He turned his attention to the pictures of Turner and Mulready, both of whom have prominent places in the National Gallery and at the Kensington Museum, and in the works of these artists Liebreich's trained sight discovered incontrovertible evidences of defective vision. These facts were brought out in 1863 by Liebreich in a communication to the Royal Institution which still lies buried among its archives.
"Till the year 1830," he says, in speaking of Turner, "all is normal. In 1831 a change in the coloring becomes for the first time perceptible, which gives to the works of Turner a peculiar character not found in any other master. Optically this is caused by an increased intensity of the diffused light proceeding from the most illuminated parts of the landscape. . . . From the year 1833 this diffusion of light becomes more and more vertical. It gradually increases during the following years. At first it can only be perceived by a careful examination of the pictures, but from the year 1839 the regular vertical streaks become apparent to every one. . . . It is a generally received opinion that Turner adopted a peculiar manner, that he exaggerated it more and more, and that his last works are the result of a deranged intellect. I am convinced of the incorrectness—I might almost say of the injustice—of this opinion. . . . According to my opinion, his manner is exclusively the result of a change in the eyes, which developed itself during the last twenty years of his life. In consequence of it, the aspect of Nature gradually changed for him, while he continued
in an unconscious, I might almost say in a naïve, manner to reproduce what he saw...."
That astigmatism distorts objects can be easily demonstrated. It is well known that the structure of the human eye is practically the same as that of the photographer's camera. Ordinarily the image which falls on the glass plate of the camera is equally clear in every part, because the lenses in front are ground with spherical surfaces. Such a camera when properly directed at a picture like that of the Taj Mahal, for example, gives us on the glass plate a clear and undistorted image of the building, such as is seen in Fig. 1. If, now, we render the front glass of the camera slightly astigmatic, by placing in front of it a so-called cylindrical glass with the axis horizontal, it produces optically exactly the same effect as that obtained when the globe of the eye is pressed from above downward. Moreover, the degree of this distortion in any eye can be reproduced with perfect exactness by placing in front of the camera a cylindrical glass of proper strength. It will be remembered that the average degree of astigmatism with the artist's examined was found to be 0·83 of a dioptre, and for this experiment I have chosen one of the lenses which is very nearly the same strength. Of course, the effect is magnified, as the camera is larger than the eye. But the eye can recognize differences infinitely more minute than those which it is possible to reproduce here, and the physiological distortion is even greater than that which it is possible to represent on the printed page. A picture taken with such a combination of lenses is shown in Fig. 2. In this it will be noticed that while the vertical lines are all clearly marked the horizontal ones are blurred and indistinct. If, now, for any reason the globe of the eye has the same distortion from side to side instead of from above downward, this can be imitated by placing the cylindrical lens before our camera with the axis vertical instead of horizontal. The result is shown in Fig. 3. The effect in this case is to blur the lines which before were clear, and make clear those which were blurred. For example, the horizontal line extending
along the top of the wall of the terrace, and even some of the strata of the stones, can be distinguished, and the horizontal lines in the building itself are also well defined. On the contrary, the vertical lines are blurred. The pillars at the top of the tower and on the dome itself are all indistinct, while, as a whole, the building is broadened and the arches are apparently wider than is shown in Fig. 2.
In all these pictures the frame also is worthy of notice. In the first it has its true proportions; and in the second, it is distorted at the sides, and in the third, above and below.
There can be no question but that astigmatism even in a slight degree materially affects what the artist sees, and if it is true that he draws what he sees, does this not mean that his drawing tends to be proportionately faulty? Nor does it affect the vision for rectangular objects alone. This distortion is a constant quantity, and it does not take very exact study to see its effect in the drawing
of the figure. For this reason, often an undue plumpness is given to some portions, while others are rendered emaciated and anæmic to a degree of which the originals were never guilty.
Another disadvantage of astigmatism to the artists is that lines really parallel appear to converge or diverge, when distorted by the blurring which astigmatism can produce. The reason of this would require too great a digression here. The practical fact is that as the blurring is unequal when different parts of the objects are differently illuminated, and as the direction of the apparent blurs depends somewhat upon the form of the object, lines which should be straight have their direction apparently changed.
This is shown in a modified way by the accompanying diagram.
If the page be tilted so as to be held in the line of vision, and if we "sight" along these heavy black lines, they are seen to be really parallel; and yet, when viewed as the page is ordinarily held, they appear inclined more or less to each other. Such an effect is produced only in exceptional cases, where the axis of the astigmatism varies in the two eyes, and this is therefore rather an unfair example. But the fact remains that the blurring of lines in certain directions may cause an artist to misrepresent very greatly the object which he is trying to reproduce.
Before leaving this phase of astigmatism it is worth while to note in passing a significant motion of the artist, already mentioned, in tipping his head from side to side, as he stands off to criticise his work. I am inclined to think he does this instinctively, in order to see better the errors in drawing caused by his own astigmatism.
The imperfect photographs of the Taj Mahal may serve to illustrate this point for some of the readers of this article. If one eye be closed (simply to exclude the correcting vision of the other), and if either of the astigmatic pictures be looked at while the book is rotated from side to side in the plane of the open page, one position can be found by most persons in which the lines are decidedly more distinct than in any other.
But, as the artist can not conveniently tip up the sides of his easel without disturbing also the equilibrium of brushes and paints and-bottles, he simply steps back and tips his head.
Moreover, the critic does the same. He, too, instinctively wishes to obtain the clearest lines—for to some these blurred, astigmatic images are confusing, disagreeable, almost painful—and to obviate that, the stranger in the studio, when he comes to see the finished picture, tips the head just as did the artist when he was at his work. The more closely we observe actions called "instinctive," the more frequently do we find they have an underlying cause.
There is another imperfection of vision, more frequently artificial and temporary than due to any structural change. This is imperfect focusing. To understand this, let us for a second time observe the artist before his easel. If he is painting a bunch of flowers, with a white rose near the center, and if he wishes this rose to stand out in strong relief, he focuses his eyes naturally and normally upon it, and reproduces on the canvas the same clearly denned, well-focused flower which he sees. To the other flowers of the cluster he does not care to give the same prominence, and sketches them with less distinctness, or else focuses his eyes purposely for a point in front of the bouquet or behind it, thus blurring the colored flowers and purposely transferring to the canvas an ill-defined image of them. For example, teachers often find fault with their pupils, saying, "The trouble is, you see too much; you should not paint so exactly." An artist, holding an important public position as a teacher of painting in Boston, recently showed me lenses which were.used by the students when learning thus to focus the objects imperfectly. Given, then, this fact of imperfect vision on the part of the artist, either in the form of astigmatism or in the form of undue contraction of the focusing muscle, let us consider its effect in relation to three factors—namely, drawing, values, and color.
As to the first, imperfect vision is unquestionably a disadvantage, as we have seen. The draughtsman owes his power to two things—accuracy of eye, which enables him clearly to perceive forms; and dexterity of hand, which enables him to reproduce them. Truth in one is as indispensable as in the other.
Next, as to the question of values. This term, as we know, is used in a certain sense to express perspective, or, more exactly, the relative distance of an object in the foreground as compared with another more or less in the background. In the case of the bouquet, just cited, the white flower in the center, having the highest relative value, is painted exactly in focus. A certain amount of artificial adjustment of focus by the artist is an undoubted advantage for the rest of the bouquet, however, and the habit of focusing the eye for some point in front of the picture or beyond it is, therefore, practically universal among artists, though in most instances they are not conscious of the act. In a similar way the effects called technically "distance" and "atmosphere" are also best secured in this way. The two factors thus far considered relate to representations in black and white as well as to those in color.
We come now to consider the third factor, that of the mixing of colors. We shall find that this involves the blurring or overlapping of images on the retina, which can be caused by astigmatism, if it exists in sufficient degree, or by improper focusing. It is usually produced by both of these together and by another function dependent on the combination and contrasting of colors. All this is done unconsciously by the observer.
To make this point clear, a slight digression is necessary to glance at the growth of painting. It must be remembered that the earlier artists were religious enthusiasts. First, they painted upon the walls of the basilicas and baptisteries; but as the early styles of architecture changed, and more and more of the wall space was encroached upon by windows, canvas came into use, and with opportunities thus increased painters grew more numerous and more proficient. Their methods of procedure were as simple as their faith, and there were but few efforts to produce unusual effects. The pigments were mixed on the palette, and thus mixed were transferred to the canvas. This was the method until recent times, and by that method the great masterpieces have been produced.
It is true that the works of some of the great colorists before which we bow down and worship to-day are not the pictures painted by these artists. The pigments they used have faded, and successive layers of varnish have changed them greatly. But in all, whether well preserved, in a slightly pathological condition, or in an advanced stage of decomposition, the point to be observed is, that the pigments were mixed on the palette just as they were placed on the canvas, and in looking at them no effort at accommodation of the eye or special focusing is required. If the eyes of the observer are opened in a natural manner, he sees just what was intended should be seen. In spite of certain variations from this type, that was the condition of the art of painting until the present generation. But, near the middle of this century a book was published by Chevreul on the Principles of Harmony and Contrasts of Colors, which by popularizing facts already known undoubtedly exerted an important influence on the artistic mind, especially in France. The principle to which I refer consists in this, that the pigments mixed on the palette and transferred to the canvas, as was the habit of earlier artists, do not produce upon the human retina so marked or so true an effect as when the proper pigments are placed unmixed but side by side on the canvas, and then viewed in such a blurred way that the rays from each are superimposed upon the retina. It is not simply a theory that the mixture of colors optically, produces effects quite different from those obtained by the mixture of corresponding pigments, but it is easily demonstrated. If we mix the rays of the spectrum, as can be done by means of a lens or concave mirror, the result is white light; but if the very same pigments, as pure as can be obtained, are mixed on the palette, we obtain not white, but a dark gray—indeed, in certain proportions we have almost a black resulting. Again, the commingling of the yellow and blue of the spectrum produces white, as was first shown by Helmholtz, but when these pigments are mixed they produce green. Such examples might be multiplied to a considerable extent. The reason why the mixture of colors in the spectrum differs in the results from the mixture of pigments is due to the fact that the pigments are not pure colors. Every red contains some blue or yellow, the yellows contain some blue or red, and the blues contain some red or yellow. Not only does the actual mixture of pigments produce effects differing from those caused by the mixture of the same colors in the eye, but the mere juxtaposition of the two pigments on the canvas influences the color of each, even when they are both properly focused in the eye. Thus, if small spots of pure yellow and blue are placed side by side, we see that the yellow inclines to red and the blue to violet. But if the spots are blurred and blended by making the eye sufficiently astigmatic by improper focusing, then by this or other optical combination it is possible to obtain shades of gray. In a word, the combination is in a "higher key." These and similar facts have been gradually worked out on the one hand in the laboratory by the physicists, and on the other by those who were constantly experimenting with pigments as they were mixed on the palette. Only a few painters know the scientific principles involved, but many had stumbled upon the practical results, and of late a new and almost distinctive class has arisen, whose usual practice it is not to mix the colors on the palette, but, consciously or unconsciously, to so arrange them on the canvas that they blend in the eye when properly viewed. This is one of the distinctive features of the so-called school of impressionists. It is easy to see that unusual care and fine artistic sense must be exercised in attempting any such trick with pigments. A genius may succeed at this, but the result for a mere imitator is disastrous. The effect is that produced when a certain artist by chance sat down on his freshly prepared palette. "Ah!" said his friend, "that is the best picture you ever produced. Cut it out, call it 'An Old-time Garden' and it will sell for a fortune." In spite of the ridicule which this class of painters has brought upon itself, it must be said in justification that the method has a certain basis of scientific truth, and that good effects, striking effects, if not the best effects, can often be obtained by this mixture of colors, not on the palette, but in the eye. But this method of arranging colors demands as its correlative a certain amount of imperfect vision. In order to see such pictures at their best, it is necessary to view them from a considerable distance, as we have seen the artist do in his studio, or else, approaching the picture, pinch the cornea by means of the lids into a marked degree of astigmatism, or, consciously or unconsciously, contract the ciliary muscle so that the eye is really focused for a point in front of the picture. Under any one of these three conditions there can be produced on the retina an overlapping of the colors, or what is termed in optics circles of diffusion. It may be mentioned in this connection that one of the most distinguished leaders to-day of the school of impressionists in France, a master who has probably done more than any other to bring that style of painting to public attention, has one eye so imperfect as to be practically useless for his painting, and the other eye is distinctly astigmatic, besides having the changes in the hardening of the lens common to advancing years. This was shown by tests which I made less than two years ago. The question might be asked, Has every impressionist a marked degree of imperfect vision from astigmatism or from other causes? While I am convinced that this is the rule, there are, of course, a great many exceptions to it. Certainly the degree of impressionistic tendency shown is by no means in proportion to the astigmatism possessed by a given artist. Various causes in the individual cases combine to influence the results. Imitation of a popular style is undoubtedly a potent factor, and many artists of late have certainly modified their previous methods in the honest desire to get more light into their pictures, as they would say, or to paint in a higher key. While the artistic instinct itself may be unchangeable from age to age, it is not strange that the expression of that instinct in painting should strive for greater perfection, and in doing so make use of any aids which science may offer.
But we must not confuse this optical trick of the impressionist with his mental condition. It is well known that when the pictures of the extremists of this school were first exhibited in the Paris Salon, they were called the works of the impressionists, for the reason that they were supposed to represent the impression of the artists at the moment. They were expressions of the lyric mood, as it were, and represented, not Nature, but the mental attitude of the painter. (If purple shadows were given to a rock, and no one else had ever seen such shadows, that was of no consequence—simply, so much the worse for the rock. Real representation was not the aim.) When the original of a portrait complained that there was not the least resemblance to himself in the picture, the impressionist replied: "Of course not. This is not photography; it is art." With some subjects such idealism is convenient. But in the extreme it shows not an astigmatism of the eye, but of the brain. The two should not be confounded.
A few practical conclusions may be drawn from our study of art and eyesight. These are briefly:
1. As far as the artist is concerned, if he wishes to avoid increasing astigmatism, it is necessary for him to abstain from this habit of making lid-pressure on the cornea, the resulting astigmatism being of no advantage, but always a disadvantage.
2. If he wishes to render himself relatively near-sighted, or, as he would state it, throw the eye out of focus, it is better to wear at his work a pair of convex glasses. The inconvenience of removing and replacing these could be obviated by spectacles made after the plan of the ordinary bifocal glasses, or, still better, by having the upper half cut away entirely, leaving for the lower a convex glass of such a strength as that individual would find most convenient for his special variety of work. In this way he is at least rid of the annoyance of constantly walking back and forward to obtain the effect of distance.
3. It is an undoubted advantage to every artist to ascertain the degree in which his eyes vary from the normal standard. Such a formula could be easily obtained. If the degree of error is but slight, of course it can be disregarded; if decided, and not properly corrected, knowledge of that variation from the normal in the artist's vision, if given in some way to the observer, would, without doubt, often win more favorable criticism for his work.
The logical and imaginative reader will perhaps picture to himself the art catalogue of the future, with a formula for the amount of imperfect vision (ametropia, as the oculists call it) added to each title. Thus:
No. 42. A Summer Morning. Myopic astigmatism, 1·5 dioptre, vertical meridian.
No. 44. He Cometh Not. Cylindrical, minus 0·5 dioptre, with spherical, minus 1·5, axis forty-five degrees.
This may seem rather like the "schedule of emotions," as it was once called, which was printed on the weekly programme in the earlier days of the Boston Symphony Orchestra, but none the less some such cataloguing of pictures would probably assist the critics and give the artist the satisfaction of more praise.
4. As the.corollary of the last proposition it should be said that the observer, in order to see a picture to the best advantage, must adjust his vision to that of the artist who produced it. Most of us do this instinctively. Not only do we select the best point of view from which to observe a picture, but we recede from the painting until the lights and colors blend in just the right degree. In addition to that, many instinctively pinch the eyes together, producing thus a momentary astigmatism, such as the artist had produced in his own eye, and find the picture thus apparently improved. A most useful appliance for viewing pictures is the so-called stenopaic slit. This is merely a slit one or two millimetres in width in a card or thin plate of brass. Simple as this device is, but few persons are aware of how much it adds to the effect in viewing paintings, as it allows the rays of light in only one meridian to pass through the cornea of the observer. If he wishes to look at a painting done by an artist whose vision is normal, or nearly so, the observer turns the slit around to correspond with the meridian of his own best vision. If, however, he looks at a picture in which it is desirable to have overlapping of the retinal images—at one, where the colors must be mixed in the eye, for example—it is necessary to rotate the slit to another position, usually at right angles to the first, and with this a canvas which before showed too clearly the blotches of color now becomes blended into a much more perfect whole. I would recommend this simple device to any one who has not already experimented with it. Thus, by adjusting our own personal equation of eyesight to that of the artist, we literally obtain his point of view. The colors are heightened, the daubs blend, and new beauties appear. Instead of seeking, like our friend mentioned at first, for "the handiest way to get out of this 'ere place," we are glad to stay longer to study and to enjoy. Here, as everywhere, it is art and science together that yield the richest result. If science is allowed to be the interpreter, we may gain a heightened enjoyment of art, and the artist a comforting increase of appreciation.