THE PHYSIOLOGICAL BASIS OF ESTHETICS 65 



No line and no form in the composition of the temple are exactly what they 

 appear to be: . . . No horizontal line is really horizontal, and no vertical line 

 really vertical, . . . every huge and massive feature is changed and almost 

 imperceptibly deflected from the appearance it bears. 8 



The free edges, namely, of the edifice instead of heing straight, as 

 in a modern architectural design, are all curved gently in the arcs of 

 large circles. The edges and vertical faces of the steps leading to the 

 portico thus have a gentle convexity outward. The surface of the 

 platform itself has the form of a very flat vault. The columns do not 

 stand exactly vertical, but slant inward and their outlines are curved 

 so that their actual thickness is greatest about one third the distance 

 from the base. So great is the radius of curvature that to the casual 

 glance there is no departure from straightness in the outlines. 



Such being the objective mechanical facts, let us see what relation 

 they may have to the visual physiology of the onlooker. 



The physiological conditions may be made clear by means of a 

 simple experiment. Let a cross formed of two strips of colored paper 

 which intersect at right angles be fastened against a neutral tinted wall 

 at the level of the eyes of the observer who stands at a distance of, say, 

 ten feet. The gaze is fixed intently for some seconds upon the center 

 of the cross. The image of the latter is thus impressed upon the retina, 

 so that when the glance is directed elsewhere upon the wall a " nega- 

 tive after-image " of the cross is projected with startling distinctness 

 upon the surface. When the eyes move so that the optic axes run along 

 either the horizontal or vertical lines extending from the center of the 

 cross the limbs of the latter maintain their true directions in the after- 

 image. But when the optic axes are directed obliquely upward or 

 downward, the cross seems to be inclined upon the wall, the vertical 

 limb leaning at a greater angle than the horizontal. When the orbital 

 movement is upward and to the right, the vertical part of the cross in- 

 clines to the right, it may be as much as fifteen degrees ; the horizontal 

 limb inclines downward to the right as much as five degrees. 9 When 

 the oblique movement of the optic axes is upward to the left the in- 

 clination of the cross is to the left. Oblique downward movements give 

 complementary results. The amount of angular inclination of the 

 after-image is proportional to the range of oblique movement. The 

 physiological explanation of this phenomenon is not here important; 

 the results are such as would occur if the eyeball in its oblique motions 

 rotated slightly like a wheel about its visual axis. 



As an observer stands before an architectural structure, his gaze 

 roving over its lines and surfaces, the extremely complex nerve-muscle 



8 "Greek Art and Modern Craftsmanship," Edinburgh Review, October, 

 1906, Vol. 204, p. 430. 



9 Le Conte, "Sight," p. 164. Internat. Scientific Series, 1881. 



VOL. LXXXI. — 5. 



