Introduction

Having thus demonstrated that the best artists have always tried to interpret nature, and express by their art an impression of nature as nearly as possible similar to that made on the retina of the human eye, it will be well to inquire on scientific grounds what the normal human eye really does see.

The Argument

Our contention is that a picture should be a translation of a scene as seen by the normal human eye. That the impression will vary with individuals, there is no doubt, for the artist will see subtleties never dreamed of by the commonplace or uneducated eye, and his aim will, of course, be to portray those subtleties in his picture, and hence one source of individuality in a work, another being in the way in which it is done. Our task now shall be to examine into the physical, physiological and psychological properties of sight, and to arrive at a conclusion, in so far as science allows us, as to how the normal eye does see things. The student will do well to read Chapter II (Lenses). of Book III. of Dr. Michael Foster's "Text Book of Physiology," as well as the matter on the eye in Ganot's Physics, before going any further in this chapter, for we do not wish to go over ground which has been occupied previously, our aim being to give a view from the artistic standpoint of the physical, physiological, and psychological properties of eyesight. We will, then, proceed to consider how well we see external nature, that is, within what limits, for we never see her exactly as she is, as we shall show.

Optic Nerves

To begin with, then, the retinal nerves are strictly reserved to respond to the vibrations of ether called light. If the student has ever had a blow on his eye, he has probably seen "stars," because every stimulus to this pair of nerves makes us see things, and not feel them. Now each sense has certain limits between which it can detect subtle vibrations, but beyond which all is blank. The more refined the organization of the person, the greater will be the number of vibrations he can distinguish. Thus 399,000,000,000 vibrations in a second produce in us the sensation of light, above this the vibrations appear as spectral colours until the number 831,000,000,000,000 is reached; to an increase in the number of vibrations above that number the optic nerve does not respond. Now the eye is an optical apparatus fixed between the brain and the ether, not that we may perceive light, for we could do that without the eye, but that we may distinguish objects. The glyptic and pictorial arts are founded entirely on the sense of sight as music is founded on the sense of hearing. In the pictorial arts, then, we must clearly distinguish between the physical, physiological, and psychological properties of sight.

Le Conte's division.

Le Conte divides the scientific, i.e. physical and physiological data, into: A. Light; B. Direction of Light; C. Intensity; D. Colour; and the psychological data into Binocular vision, size, solidity, and depth. Following up Le Conte's scheme, let us begin, then, to discuss briefly the scientific data, that is, considering the apparatus purely from the standpoint of physics and physiology.