of astigmatism, which decidedly dis- racter and intellectual individuality. turb vision, are, however, not uncom. His admirers considered even the mamon, and are therefore also found among terial resemblance of his portraits as painters. I have had occasion to ex- perfect; most people, however, thought amine the eyes of several distinguished he had intentionally neglected the maartists which presented such an anomaly, terial likeness by rendering in an indisand it interested me much to discover tinct and vague manner the details of what influence this defect had upon the features and the forms. A careful their works. The diversity depends in analysis of the picture shows that this part upon the degree and nature of the indistinctness was not at all intentional, optical anomaly, but its effect shows but simply the consequence of astigmaitself in different ways, according to tism. Within the last few years the the subjects the artist paints. An portraits of this painter have become example will explain this better. I considerably worse, because the former know a landscape-painter and a por- indistinctness has grown into positively trait-painter who have both the same false proportions. The neck and oval kind of astigmatism; that is, the re- of the face appear in all his portraits fraction of the vertical meridian differs considerably elongated, and all details from the refraction of the horizontal are in the same manner distorted. What one. The consequence is, that their is the cause of this? Has the degree of sight is normal for vertical lines, but his astigmatism increased ? No; this for horizontal lines they are slightly does not often happen : but the effect of short-sighted. Upon the landscape- astigmatism has doubled, and this has painter this has hardly any disturbing happened in the following manner :influence. In painting distant views An eye which is normal as regards the sharp outlines are not requisite, but vision of vertical lines, but short-sighted rather undefined and blending tones of for horizontal lines, sees the objects eloncolour. His eye is sufficiently normal gated in a vertical direction. When the to see these. I was struck, however, time of life arrives that the normal eye by the fact that the foreground of his becomes far-sighted, but not yet the shortpictures, which generally represents sighted eye, this astigmatic eye will at water with gently-moving waves, was short distance see the vertical lines innot painted with the same truthfulness distinctly, but horizontal lines still disto nature as the middle and back-ground. tinctly; and therefore near objects will There I found short horizontal strokes be elongated in a horizontal direction. of the brush in different colours, which The portrait-painter, in whom a slight did not seem to belong to the water. I degree of astigmatism manifested itself therefore examined the picture with a at first only by the indistinctness of the glass, which, when added to my eye, horizontal lines, has now become farproduced the same degree of astigmatism sighted for vertical lines, and therefore as existed in the painter's eye, and the sees a distant person elongated in a whole picture appeared much more vertical direction; his picture, on the beautiful, the foreground being now as contrary, being at a short distance, is seen perfect as the middle and back-ground. by him enlarged in a horizontal direction, In consequence of this artiticially and is thus painted still more elongated produced astigmatism, I saw the hori- than the subject is seen : so the fault is zontal strokes of the brush indistinctly doubled. I shall be able to show this and so mixed together, that through them more clearly by experiments. the colour and transparency of the water The vertical and horizontal lines of were most exquisitely rendered.

this diagram (Fig. 1) are reflected with Upon the portrait-painter astigmatism equal distinctness upon the screen by had a very different influence. He the spherical apparatus. was held in high esteem in Paris, on Those among my audience who have account of his excellent grasp of cha 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.

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 illumi. nated red can be perceived as such, while a less intense red appears green. This moderate degree of colour-blindness does not always deter people from paint ing. 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.

It can of course only produce optical yellowish, and consequently he will delusions, never a real optical identity; paint it too blue. Does he not perceive that is to say, the image which is traced this himself? Does he not believe it in our eye by real objects is not identical if told of it? Were this the case, it with the image produced in our eye by would be easy for him to correct the the picture. This is best observed by fault, since an artist can paint in a changing the light. Whoever paints in yellower or bluer tone, as he chooses. London has but too frequent opportu- These are two questions which are nities of observing this. A little more easily answered by psychological exor less fog, the reflection of a cloud illu- perience. He does not perceive it minated by the sun, suffices to alter en- himself, because he does not remember tirely the colouring of the picture, while that he formerly saw in a different the colouring of natural objects is not way. Our remembrance with regard changed in the same manner.

to opinions, sensations, perceptions, &c. Let us now return to our experiment which have become gradually modified with the yellow glass, and we shall find in the course of years—not by any that it affects our eye very much in the external influence or sudden impression, same way as a yellow tint in the light, but by a gradual change in our own and therefore modifies natural objects in physical or mental individuality-is quite a different degree from pictures. almost nil. If we continue the experiment for a He does not believe it I would not considerable time, the difference becomes say because an artist rarely recognizes more and more essential. As I said what others tell him with regard to his before, the eye becomes dulled with works, but because with hini, as with regard to the yellow light, and thus sees everyone else, the impressions received nature again in its normal colouring through his own eye have a stronger The small quantity of blue light which power of conviction than anything else. is excluded by the yellow glass produces “Sehen geht vor Sagen” (Seeing is beno sensible difference, as the difference lieving), says the old adage. is equalized by a diminution of sensi We are almost always conscious of bility with regard to yellow. In the indistinct vision, be it in consequence picture, on the contrary, there is found of incorrect accommodation or insuffin many places only as much blue as is cient power of sight, especially if it perfectly absorbed by the yellow glass, is not congenital, but has gradually and this therefore can never be perceived appeared. But it is extremely difficult however long we continue the experi- and in many cases impossible to conment. Even for those parts of the pic- vince those of their defect who suffer ture which have been painted with the from incorrect vision as to form and most intense blue the painter could colour. They never become conscious produce, the quantity of blue excluded of it themselves, even if it is not by the yellow glass will make itself felt, congenital, and the most enlightened because its power is not so small with and intelligent among them remain regard to pigments as with regard to incredulous, or become even angry and the blue in nature.

offended, when told of it. Incorrect Imagine now that in the course of perception of form may, however, easily years one of the transparent media in be demonstrated. If in consequence the eye of a painter had gradually be- of astigmatism a square appears oblong come yellowish, and that this yellow to anyone, he can measure the sides had by degrees considerably increased in with a compass; or, what is more simple intensity, and you will easily understand still, he can turn it so that the horithe intluence it must exercise upon zontal lines are changed into vertical his work. He will see in nature ones, and vice versá, and his own sight almost everything correctly ; but in his will convince him of his error. It is picture everything will appear to him 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 à 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 Mulically. 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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