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
