December 31, 1891] 



NA TURE 



203 



the careless workmanship of an optician who offered him 

 for sale an instrument with similar defects, and that he 

 would emphatically refuse to take it." The eye being 

 the chief organ of artists, its defects are of great im- 

 portance in art and its history, and artists would do well 

 to inform themselves, not only on these defects in general, 

 but more particularly on those which they, in their own 

 persons, are subject to ; for, as Bessel remarked of 

 astronomical instruments, "an error once well ascertained 

 ceases to be an error." 



Our conception of the stars as stars, in the shape 

 adopted symbolically by decorative art, is caused by a 

 defect of the eye closely related to irradiation ; stars 

 being luminous spots in the sky without rays, as they 

 actually appear to a privileged few. Prof. Exner, 

 whose line of thought we shall repeatedly cross in the 

 course of these reflections, justly remarks that to this 

 imperfection the stars conferred by Sovereigns as marks 

 of distinction owe their origin, and star-fishes their name, 

 even since Pliny's time. The different varieties of halo, 

 however, are more probably free-born children of our 

 fancy — from the Byzantine massive golden disk, down to 

 the mild phosphorescence proceeding from holy heads 

 and in Correggio's " Night " from the entire child, which 

 illumines the scene with a light of its own. According 

 to Prof. Exner, glories of the latter description are 

 derived from the radiance which surrounds the shadow 

 of one's own head in the sunshine on a dewy meadow, 

 and which in fact has always been compared to halos 

 in religious pictures. This phenomenon even misled 

 Benvenuto Cellini into the pious delusion that it was a gift 

 granted him individually from above, and a reflection of his 

 visions, such as Moses brought down from Mount Sinai. ^ 



Certain otherwise quite inexplicable peculiarities which 

 disfigure the later works of the distinguished landscape- 

 painter Turner have also been traced to defects of the 

 eye by Dr. Richard Liebreich.- Clouded lenses or a high 

 degree of astigmatism might easily lead a painter to 

 distort or blur objects he was copying . from nature. 

 Donders's stenopeic spectacles or cylindrical spectacles, 

 as the case might be, would prove as useful to such an 

 artist as concave glasses to the shortsighted. 



The singularities of another English painter, Mulready, 

 are accounted for by Dr. Liebreich through discoloration 

 of the lens from old age. Another defect of the eye — 

 colour-blindness — ought to be mentioned here, which 

 in its milder forms is of frequent occurrence, and even 

 belongs to the normal condition of the eye on the borders 

 of the field of vision. It corresponds in the domain of 

 hearing to the want of musical ear. Colour-bhndness was 

 known long ago, but has been inquired into with re- 

 doubled zeal latterly, partly with regard to its general 

 connection with chromatics, partly on account of its 

 serious practical consequences in the case of sailors, 

 railway officials, and, as Dr. Liebreich adds, of painters. 

 Both colour-blindness and want of ear are inborn defects, 

 for which there is no remedy. A colour-blind artist is, 

 however, better off than a musician without an ear, if 

 such a one were imaginable, for, even if he neglected the 

 modelling stick and the chisel, he might still seek his 

 fortune in the designing of cartoons. 



It is difficult to determine the particular point where 

 optical knowledge ceases to be of use to artists. None 

 will repent having studied the laws of the movement of 

 the eyes, the difference between near and distant vision, 

 and the observations on the expression of the human eye 

 contained in John Miiller's early work on " Comparative 

 Physiology of Sight." Yet it must be admitted that a 

 painter may paint an eye exceedingly well without ever 

 having heard of Sanson's images, which cause the soft 

 lustre of a gentle eye as well as the fierce flash of an 



' "Vitadi Benvenuto Cellini, tcntta dalui medesimo,"libro primo, cxxvii. 

 ^ "Turner and Mulready : the Effect of ceriain Faults of Vision on Paint- 

 ing, &c.," Londiin, 1888. 



NO. 1157, VOL. 45] 



angry one ; as little as the blue sky of a landscape painter 

 will gain by his knowledge of the yellow brushes in every 

 great circle of the heavenly vault which passes through 

 the sun — a phenomenon which has remained unnoticed 

 for countless ages, but has grown familiar to physiologists 

 since Haidinger's discovery. 



One point, however, where physicists seem to me not 

 to have been sufficiently consulted, is the much-debated 

 question of polychrome in ancient statues and architecture, 

 and whether it should be adopted by modern art or not. 

 Physical experiments teach that very intense illumination 

 causes all colours to appear whitish ; in the spectrum of 

 the sun, seen immediately through the telescope, the 

 colours vanish almost entirely, nothing remaining except 

 a light yellow hue in the red end. As the colours grow 

 whitish the glaring contrasts are softened, they blend 

 more harmoniously. In the open air, therefore, our eye is 

 not shocked by the scarlet skirt of the contadina, which 

 recurs almost as invariably in Oswald Achenbach's 

 Campagna landscapes, as the white horse in Wouver- 

 manns's war scenes. The Greek statues and buildings 

 may have looked well enough with their glaring 

 decorations under the bright southern sky on the 

 Acropolis or in the Poikile ; in the dull light of our 

 northern home, above all in closed rooms, they are some- 

 what out of place. 



In another direction Wheatstone has added valuable 

 information to the knowledge of painters and designers 

 with his stereoscope. It demonstrates the fundamental 

 difference which distinguishes binocular vision of near 

 objects from monocular vision, as well as from binocular 

 vision of objects so far removed that the distance between 

 the eyes vanishes as compared with their distance. An 

 impression of solidity can only be obtained by each eye 

 getting a different view of an object, the two images being 

 fused into one, so as to appear solid. A painter can 

 therefore only express depth by shading and aerial per- 

 spective ; he will never be able to produce the impression 

 of actual solidity on his canvas. While Wheatstone's 

 pseudoscope exhibits the unheard-of spectacle of a con- 

 cave human face, Helmholtz's telestereoscope magnifies, 

 as it were, the space between the eyes, and resolves a far- 

 off range of woods or hills without aerial perspective into 

 its different distances. Finally, Halske's stereoscope with 

 movable pictures confirms old Dr. Robert Smith's 

 explanation of the much-debated circumstance that the 

 sun and moon on the horizon appear larger by almost a 

 fifth of their diameter than when seen in the zenith, and 

 reduces the problem to the other question : why the 

 vault of the sky appears to us flattened instead of 

 hemispherical. 



However, the almost contemporary invention of photo- 

 graphy was destined to be of vastly greater importance to 

 the fine arts. It had always been the dream of artists 

 as well as physicists to fix della Porta's charming pictures 

 — a dream the realization of which did not seem quite 

 impossible since the discovery of chloride of silver. One 

 must have witnessed Daguerre's invention, and Arago's 

 report of it in the Chamber of Deputies, to conceive 

 the universal enthusiasm with which it was welcomed. 

 Daguerre's method, being complicated and of restricted 

 application, was soon cast into the shade by the one still 

 essentially practised at the present day. However, it is 

 worth recording that, when the first specimens, imperfect 

 as they were, reached us from England, no one foresaw 

 the immense success in store for Talbotypes ; on the 

 contrary, the change from silver-coated plates to paper 

 impregnated with the silver salt was received with doubt, 

 and considered a retrogression. 



Thus photography entered on its marvellously vic- 

 torious career. With respect to art it promptly fulfilled 

 what Arago had promised in its name. It not only 

 facilitated the designing of architecture, interiors, and 

 landscapes, and rendered the camera clara unnecessary 



