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
