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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 artificially 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,
nevertheless, see them differently. Those (Fig. 3): if I add a cylindrical concave
glass, with its axis placed horizontally, FIGLI
the square becomes an oblong.
In order now to show you how it is possible that the same eye may see an
whose sight is normal will only observe a difference after I have added a cylindrical lens to this apparatus, and thus object at too great a distance elongated made it astigmatical (Fig. 2). Ordinary in a vertical direction, and, on the conFIGE
trary, one that is too near enlarged in a horizontal direction, I need only place this cylindrical glass before or behind the focus of the apparatus without turning the axis, and you will then see the square, first elongated in a vertical direction (Fig. 4), and then enlarged in a horizontal direction.
spectacle glasses are worked by a rotating movement on the surface of a sphere; cylindrical lenses are worked by moving the glass backwards and forwards upon a cylindrical surface. Such glasses produce an optical effect only in one direction. If instead of white lines I make the experiment with coloured lines, it will show the mixing of colours produced by astigmatism; and if I now turn the axis of the lens, you will observe the effect of different forms of astigmatism. I show you here a square
Lastly, I show you a portrait. Imagine to yourself that it represents the person whom the astigmatical painter is painting; then, by aid of the cylindrical glass you can form an idea how the painter sees this person.
If I alter the position of the glass,
the portrait assumes the form in which They do not arise from a deficient functhe painter sees bis own painting on tion of the nervous apparatus of the eye, the canvas.
This will explain to you but in consequence of a change in the why he paints the portrait still longer colour of the lens. than he sees the person.
The lens always gets rather yellow at With regard to an anomaly of sight, an advanced age, and with many people which seems almost foreign to the the intensity of the discoloration is subject of painting-I mean colour considerable. This, however, does not blindness—I will also say a few words essentially diminish the power of vision. here, as the subject seems to be re In order to get a distinct idea of the garded with particular interest in effect of this discoloration, it is best England.
to make experiments with yellow glasses What we call colour-blindness is a con of the corresponding shade. Only the genital defect of vision, which is charac- experiment must be continued for some terized by the absence of one of the three time, because at first everything looks primary sensations of colour. The pri- yellow to us. But the eye gets soon mary sensations of colour are red, green, accustomed to the colour, or rather it and violet, according to Thomas Young becomes dulled with regard to it, and and Helmholtz ; or red, green, and blue, then things appear again in their true according to Maxwell
. When, as may light and colour. This is at least the easily happen, to this defect is joined a case with all objects of a somewhat decided talent for painting, drawing bright and deep colour. A careful exalone ought to be attempted, because so amination, however, shows that a pale absolute a defect will soon assert itself. blue, or rather a certain small quantity But we meet with slighter degrees of of blue, cannot be perceived even after colour-blindness, where the perception a very prolonged experiment, and after of red is not entirely wanting, but only the eye has long got accustomed to the considerably diminished ; so that, for yellow colour, because the yellow glass instance, an intense or strongly illumi really excludes it. This must, of course, nated red can be perceived as such, while exercise a considerable influence when a less intense red appears green. This looking at pictures, on account of the moderate degree of colour-blindness great difference which necessarily exists does not always deter people from paint between real objects and their representaing. A proof of this I saw at the last tion in pictures. year's Exhibition, in a picture which re These differences are many and great, presented a cattle market. The roofs of as has been so thoroughly explained the surrounding houses were all painted by Helmholtz. Let us for a moment red on the sunny side, green in the waive the consideration of the difshadow; but—what particularly struck ference produced by transmitting an me—the oxen also were red in the object seen as a body on to a simple sun, green in the shadow. The slighter flat surface, and consider only the degrees of this anomaly, in the form of intensity of light and colour. The an insufficient perception of colours, intensity of light proceeding from the have probably been the real cause why sun and reflected by objects, is so infiseveral great artists, who have become nitely greater than the strongest light famous on account of the beauty of their reflected from a picture, that the prodrawing and the richness of their com portion expressed in numbers is far bepositions, have failed to attain an equal yond our comprehension. There is also degree of perfection in colouring. so great a difference between the colour
In opposition to these isolated cases, of light, or of an illuminated object, I have to draw your attention to other and the pigments employed in painting, cases which happen more frequently, that it appears wonderful that the and in advanced age, in consequence of art of painting can by the use of them a change in the perception of colours. 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 regarl to his before, the eye becomes dulled with works, but because with hinı, 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 insuffiin 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 influence it must exercise upon zontal lines are changed into vertical
his work. He will see in nature ones, and vice versa, 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. characteristic a tone of colour, that I Such glaring mistakes as those pro could easily point them out while passduced by colour-blindness can be easily ing through a picture gallery. As a recognized, but faults produced by striking example I will only mention a diminished sensation of small differ Mulrcady. It is generally stated that ences in the shades of colour can in his advanced age he painted too only be recognized as such by the fact purple. A careful examination shows that the majority of persons with that the peculiarity of the colours of normal vision declare them to be faults. of his later pictures is produced by an Such, for instance,
deviations addition of blue. Thus, for instance, produced by an incorrect percep the shadows on the flesh are painted in tion of pigments, which in painting pure ultramarine. Blue drapery he makes itself felt by a constantly
constantly painted most unnaturally blue. Red recurring plus or minus of a single of course became purple. If you
look colour in the whole picture.
at these pictures through a yellow glass, also show itself by small faults in the all these faults disappear : what forrendering of every colour. In discussing merly appeared unnatural and disthis subject with artists, they at once pleasing is at once corrected; the violet declare these anomalies to represent a colour of the face shows a natural red; school, a taste, a manner, which may be the blue shades become grey; the arbitrarily changed. They most un unnatural glaring blue of the drapery willingly concede that peculiarities of is softened. To make the correction sight have anything to do with it. It perfect, the glass must not be of a seems to me sometimes as if they bright gold colour, but rather of the considered it in a certain measure a colour of pale sherry. It must be degradation of their art that it should gradually darkened in accordance with be influenced by an organ of sense, and the advancing age of the painter, not depend entirely upon free choice, and will then correspond exactly with intelligence, imagination, and talent. the colour of his lens. The best
Thus, to return to the point from proof of the correctness of this statewhich we started, if a painter whose ment is, that the yellow glass not only lens becomes yellower begins to paint modifies the blue in Mulready's picin a bluer tone, it is said that he tures, but gives truthfulness to all the has changed his style. The painter other colours he employed. To make himself vehemently protests against the proof complete, it would be necesthis opinion ; he thinks that he still sary to show that by the aid of yellow paints in his old style, and that he has glass we saw Mulready's pictures as only imprɔved the tone of his colour. he saw them with the naked eye; and His earlier works appear to him too this can be proved. It happens that brown. To convince him of his error Mulready has painted the same subit would be necessary to remove his ject twice,—first in 1836, when he was lens suddenly. Then everything would fifty years of age and his lens was appear to him too blue, and his paint in a normal state, and again in 1857, ings far too blue. This is no hypo- when he was seventy-one, and the thesis, but a fact. Patients on whom yellow discoloration had considerably I have operated for cataract, very often advanced. The first picture was called spontaneously declared, immediately after when exhibited “Brother and Sister; the operation, that they saw everything or, Pinching the Ear;” the second was blue; in these cases I invariably found called “The Young Brother.” In both their crystalline lens to be of an intense pictures a girl, whose back only is visible, yellow colour. In pictures painted after is carrying a little child. the artists were considerably over sixty, peasant, in a blue smock-frock, stands the effect of the yellow lens can often be to the right and seizes the ear of the studied. To me their pictures have so child. The background is formed by a