LIGHT AND SHADE.* We are able to distinguish objects owing to our ability to dis cern differences in brightness and in hue or differences in light, shade and color. If we did notpossess the gift of color-vision the magical drapery of color would disappear and the gray of dawn would persist throughout the day. The color-blind eye, which is otherwise normal, secs only the series of neutral grays from white and black. These the artist terms "values." Brief consideration is convincing that "Light and Shade" is an extensive subject of great importance to us because of its relation to vision, to the appearance of objects, to the imitation of objects and to everything, with the exception of hue, which appeals to human con sciousness through the doorway of vision. Al though color is useful and appealing to man, generally he is much less conscious of its exist ence than he is of form, or brightness distribu tion. It is the distribution and modulation of light and shade which model form, so that as an essential to vision the perception of color is much less important than the perception of "values" or brightnesses.
Objects are visible usually because they emit light either by transmission or by reflec tion but there must be a contrast either in brightness or in hue in order that they be dis tinguishable from their surroundings. Further more, objects are modelled by the distribution of light, shade and color upon their surfaces. In order to eliminate the necessity of including color in the present discussion the objects which may be considered will be assumed to have neutral surfaces, that is, white or gray. Even the surface characteristics of objects play an important part in their appearances. There are many kinds of surfaces from the regularly reflecting mirror to the diffusely reflecting sur face such as blotting paper, or powdered zinc oxide. A study of these surfaces and of their appearances under different kinds of lighting is of vast importance in relation to vision-and to the imitative arts.
For example, assume two gray spheres, iden tical in every respect except that one has a glossy surface and the other a dull one. If lighted by a small light-source at a considerable distance from them, they will appear identical when in the same position with respect to the light-source except for the brilliant high-light on the glossy sphere. This high-light
is an image of the light-source formed by the glossy convex surface. If the surface is optically convex the image will be seen to be reproduced in accurate minute detail. If the two spheres be illuminated outdoors under an overcast sky, the comparatively less brilliant high-light will extend over a large area and will be unnoticed. The minute high-light of the small light-source in general will not be at-a point on the sphere nearest the light-source or the observer but will be found to lie on an element of surface which is so oriented that the angle of incidence of the beam from the source is equal to the angle of reflection of the beam of light reaching the eye by regular re flection from the object. On changing his position the observer will note that the position of the high-light Changes so that this simple law of optics is always fulfilled.
The character of the lighting has much to do with the appearance of an object. If the dull sphere receives equal amounts of light frOm all directions it will not appear spherical but will appear to be a flat disc. No modulation of light and shade is present to model it. If the glossy sphere be placed at the centre of a diffusing glass globe which is uniformly illumi nated over its exterior, the sphere will appear: flat. However, under most conditions the brilliant high-lights will reveal its form under lighting conditions which would "flatten" the dull sphere.
Metallic moldings owe their appearance quite predominantly to these bright high-lights which are more or less perfect images of the light-sources. It is interesting to note the effect of the medium on the expression of sculptured objects. A Venus in white marble of dull sur face is most beautifully expressive of tht human body but the same figure in polished bronze is sometimes hideous with grotesque metallic high-lights. These effects are illus trated in Figs. 1 and 2, respectively. On the other hand, a bay horse may be well represented in polished bronze and the appearance of a sculpture of a swarthy-skinned Indian is quite congruous if done in semi-polished bronze. This does not mean that the artist may not dis play his skill in any medium but it brings forth the fact that the medium influences the final appeal of the sculpture to us through the appearance for which it is partly responsible.