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of astigmatism, which decidedly disturb vision, are, however, not uncommon, and are therefore also found among painters. I have had occasion to examine the eyes of several distinguished artists which presented such an anomaly, and it interested me much to discover what influence this defect had upon their works. The diversity depends in part upon the degree and nature of the optical anomaly, but its effect shows itself in different ways, according to the subjects the artist paints. An example will explain this better. I know a landscape-painter and a portrait-painter who have both the same kind of astigmatism; that is, the refraction of the vertical meridian differs from the refraction of the horizontal

one.

The consequence is, that their sight is normal for vertical lines, but for horizontal lines they are slightly short-sighted. Upon the landscapepainter this has hardly any disturbing influence. In painting distant views sharp outlines are not requisite, but rather undefined and blending tones of colour. His eye is sufficiently normal to see these. I was struck, however, by the fact that the foreground of his pictures, which generally represents water with gently-moving waves, was not painted with the same truthfulness to nature as the middle and back-ground. There I found short horizontal strokes of the brush in different colours, which did not seem to belong to the water. therefore examined the picture with a glass, which, when added to my eye, produced the same degree of astigmatism as existed in the painter's eye, and the whole picture appeared much more beautiful, the foreground being now as perfect as the middle and back-ground. In consequence of this artificiallyproduced astigmatism, I saw the horizontal strokes of the brush indistinctly and so mixed together, that through them the colour and transparency of the water were most exquisitely rendered.

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Upon the portrait-painter astigmatism had a very different influence. He was held in high esteem in Paris, on account of his excellent grasp of cha

racter and intellectual individuality. His admirers considered even the material resemblance of his portraits as perfect; most people, however, thought he had intentionally neglected the material likeness by rendering in an indistinct and vague manner the details of the features and the forms. A careful analysis of the picture shows that this indistinctness was not at all intentional, but simply the consequence of astigmatism. Within the last few years the portraits of this painter have become considerably worse, because the former indistinctness has grown into positively false proportions. The neck and oval of the face appear in all his portraits considerably elongated, and all details are in the same manner distorted. What is the cause of this? Has the degree of his astigmatism increased? No; this does not often happen: but the effect of astigmatism has doubled, and this has happened in the following manner:An eye which is normal as regards the vision of vertical lines, but short-sighted for horizontal lines, sees the objects elongated in a vertical direction. When the time of life arrives that the normal eye becomes far-sighted, but not yet the shortsighted eye, this astigmatic eye will at short distance see the vertical lines indistinctly, but horizontal lines still distinctly; and therefore near objects will be elongated in a horizontal direction. The portrait-painter, in whom a slight degree of astigmatism manifested itself at first only by the indistinctness of the horizontal lines, has now become farsighted for vertical lines, and therefore sees a distant person elongated in a vertical direction; his picture, on the contrary, being at a short distance, is seen by him enlarged in a horizontal direction, and is thus painted still more elongated than the subject is seen: so the fault is doubled. I shall be able to show this more clearly by experiments.

The vertical and horizontal lines of this diagram (Fig. 1) are reflected with equal distinctness upon the screen by the spherical apparatus.

Those among my audience who have a decided form of astigmatism will,

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the portrait assumes the form in which the painter sees his own painting on the canvas. This will explain to you why he paints the portrait still longer than he sees the person.

With regard to an anomaly of sight, which seems almost foreign to the subject of painting-I mean colourblindness-I will also say a few words here, as the subject seems to be regarded with particular interest in England.

This

What we call colour-blindness is a congenital defect of vision, which is characterized by the absence of one of the three primary sensations of colour. The primary sensations of colour are red, green, and violet, according to Thomas Young and Helmholtz; or red, green, and blue, according to Maxwell. When, as may easily happen, to this defect is joined a decided talent for painting, drawing alone ought to be attempted, because so absolute a defect will soon assert itself. But we meet with slighter degrees of colour-blindness, where the perception of red is not entirely wanting, but only considerably diminished; so that, for instance, an intense or strongly illuminated red can be perceived as such, while a less intense red appears green. moderate degree of colour-blindness does not always deter people from painting. A proof of this I saw at the last year's Exhibition, in a picture which represented a cattle market. The roofs of the surrounding houses were all painted red on the sunny side, green in the shadow; but-what particularly struck me-the oxen also were red in the sun, green in the shadow. The slighter degrees of this anomaly, in the form of an insufficient perception of colours, have probably been the real cause why several great artists, who have become famous on account of the beauty of their drawing and the richness of their compositions, have failed to attain an equal degree of perfection in colouring.

In opposition to these isolated cases, I have to draw your attention to other cases which happen more frequently, and in advanced age, in consequence of a change in the perception of colours.

They do not arise from a deficient function of the nervous apparatus of the eye, but in consequence of a change in the colour of the lens.

The lens always gets rather yellow at an advanced age, and with many people the intensity of the discoloration is considerable. This, however, does not essentially diminish the power of vision. In order to get a distinct idea of the effect of this discoloration, it is best to make experiments with yellow glasses of the corresponding shade. Only the experiment must be continued for some time, because at first everything looks yellow to us. But the eye gets soon accustomed to the colour, or rather it becomes dulled with regard to it, and then things appear again in their true light and colour. This is at least the case with all objects of a somewhat bright and deep colour. A careful examination, however, shows that a pale blue, or rather a certain small quantity of blue, cannot be perceived even after a very prolonged experiment, and after the eye has long got accustomed to the yellow colour, because the yellow glass. really excludes it. This must, of course, exercise a considerable influence when looking at pictures, on account of the great difference which necessarily exists between real objects and their representation in pictures.

These differences are many and great, as has been so thoroughly explained by Helmholtz. Let us for a moment waive the consideration of the difference produced by transmitting an object seen as a body on to a simple flat surface, and consider only the intensity of light and colour. The intensity of light proceeding from the sun and reflected by objects, is so infinitely greater than the strongest light reflected from a picture, that the proportion expressed in numbers is far beyond our comprehension. There is also so great a difference between the colour of light, or of an illuminated object, and the pigments employed in painting, that it appears wonderful that the art of painting can by the use of them produce such perfect optical delusions.

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It can of course only produce optical delusions, never a real optical identity; that is to say, the image which is traced in our eye by real objects is not identical with the image produced in our eye by the picture. This is best observed by changing the light. Whoever paints in London has but too frequent opportunities of observing this. A little more or less fog, the reflection of a cloud illuminated by the sun, suffices to alter entirely the colouring of the picture, while the colouring of natural objects is not changed in the same manner.

Let us now return to our experiment with the yellow glass, and we shall find that it affects our eye very much in the same way as a yellow tint in the light, and therefore modifies natural objects in quite a different degree from pictures. If we continue the experiment for a considerable time, the difference becomes more and more essential. As I said before, the eye becomes dulled with regard to the yellow light, and thus sees nature again in its normal colouring. The small quantity of blue light which is excluded by the yellow glass produces no sensible difference, as the difference is equalized by a diminution of sensibility with regard to yellow. In the picture, on the contrary, there is found in many places only as much blue as is perfectly absorbed by the yellow glass, and this therefore can never be perceived however long we continue the experiment. Even for those parts of the picture which have been painted with the most intense blue the painter could produce, the quantity of blue excluded by the yellow glass will make itself felt, because its power is not so small with regard to pigments as with regard to the blue in nature.

Imagine now that in the course of years one of the transparent media in the eye of a painter had gradually become yellowish, and that this yellow had by degrees considerably increased in intensity, and you will easily understand the influence it must exercise upon his work. He will see in nature almost everything correctly; but in his picture everything will appear to him

yellowish, and consequently he will paint it too blue. Does he not perceive this himself? Does he not believe it if told of it? Were this the case, it would be easy for him to correct the fault, since an artist can paint in a yellower or bluer tone, as he chooses. These are two questions which are easily answered by psychological experience. He does not perceive it himself, because he does not remember that he formerly saw in a different way. Our remembrance with regard to opinions, sensations, perceptions, &c. which have become gradually modified in the course of years-not by any external influence or sudden impression, but by a gradual change in our own physical or mental individuality—is almost nil.

He does not believe it-I would not say because an artist rarely recognizes what others tell him with regard to his works, but because with him, as with everyone else, the impressions received through his own eye have a stronger power of conviction than anything else. "Sehen geht vor Sagen" (Seeing is believing), says the old adage.

We are almost always conscious of indistinct vision, be it in consequence of incorrect accommodation or insufficient power of sight, especially if it is not congenital, but has gradually appeared. But it is extremely difficult and in many cases impossible to convince those of their defect who suffer from incorrect vision as to form and colour. They never become conscious of it themselves, even if it is not congenital, and the most enlightened and intelligent among them remain incredulous, or become even angry and offended, when told of it. Incorrect perception of form may, however, easily be demonstrated. If in consequence of astigmatism a square appears oblong to anyone, he can measure the sides with a compass; or, what is more simple still, he can turn it so that the horizontal lines are changed into vertical ones, and vice versa, and his own sight will convince him of his error. It is more difficult to demonstrate whether

a person sees colours correctly or not. Such glaring mistakes as those produced by colour-blindness can be easily recognized, but faults produced by a diminished sensation of small differences in the shades of colour can only be recognized as such by the fact that the majority of persons with normal vision declare them to be faults. Such, for instance, are deviations produced by an incorrect perception of pigments, which in painting makes itself felt by a constantly recurring plus or minus of a single colour in the whole picture. It may also show itself by small faults in the rendering of every colour. In discussing this subject with artists, they at once declare these anomalies to represent a school, a taste, a manner, which may be arbitrarily changed. They most unwillingly concede that peculiarities of sight have anything to do with it. It seems to me sometimes as if they considered it in a certain measure a degradation of their art that it should be influenced by an organ of sense, and not depend entirely upon free choice, intelligence, imagination, and talent.

Thus, to return to the point from which we started, if a painter whose lens becomes yellower begins to paint in a bluer tone, it is said that he has changed his style. The painter himself vehemently protests against this opinion; he thinks that he still paints in his old style, and that he has only improved the tone of his colour. His earlier works appear to him too brown. To convince him of his error it would be necessary to remove his lens suddenly. Then everything would appear to him too blue, and his paintings far too blue. This is no hypothesis, but a fact. Patients on whom I have operated for cataract, very often spontaneously declared, immediately after the operation, that they saw everything blue; in these cases I invariably found their crystalline lens to be of an intense yellow colour. In pictures painted after the artists were considerably over sixty, the effect of the yellow lens can often be studied. To me their pictures have so

characteristic a tone of colour, that I could easily point them out while passing through a picture-gallery. As a striking example I will only mention Mulready. It is generally stated that in his advanced age he painted too purple. A careful examination shows that the peculiarity of the colours of of his later pictures is produced by an addition of blue. Thus, for instance, the shadows on the flesh are painted in pure ultramarine. Blue drapery he painted most unnaturally blue. Red of course became purple. If you look at these pictures through a yellow glass, all these faults disappear: what formerly appeared unnatural and displeasing is at once corrected; the violet colour of the face shows a natural red; the blue shades become grey; the unnatural glaring blue of the drapery is softened. To make the correction perfect, the glass must not be of a bright gold colour, but rather of the colour of pale sherry. It must be gradually darkened in accordance with the advancing age of the painter, and will then correspond exactly with the colour of his lens. The best proof of the correctness of this statement is, that the yellow glass not only modifies the blue in Mulready's pictures, but gives truthfulness to all the other colours he employed. To make the proof complete, it would be necessary to show that by the aid of yellow glass we saw Mulready's pictures as he saw them with the naked eye; and this can be proved. It happens that Mulready has painted the same subject twice,-first in 1836, when he was fifty years of age and his lens was in a normal state, and again in 1857, when he was seventy-one, and the yellow discoloration had considerably advanced. The first picture was called when exhibited "Brother and Sister; or, Pinching the Ear;" the second was called "The Young Brother." In both pictures a girl, whose back only is visible, is carrying a little child. A young peasant, in a blue smock-frock, stands to the right and seizes the ear of the child. The background is formed by a

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