Motion Picture News (May-Jun 1923)

2692 Motion Picture News Smooth Movement of Pictures Explained Description of Qualities of Eye and Vision that Permit Phenomena By DONALD A. LAIRD University of Iowa * THE story of the development of the motion picture industry is a fascinating hit of history in financial organization and international trade competition. Why the movies move is as fascinating a morsel from the recent history of applied science and the progress of mechanics. The present excellence of clearness, freedom from the dicker, and the illusion of motion in the movie are due to the ingenious application and capitalization of certain facts primarily from the field of psychology. It will be necessary to review these interesting discoveries in order to establish a basis for an understanding of why these pictures, which are really intermittent, motionless and flat, nevertheless appear to be continuous in motion and to possess depth. Three Questions to Answer There are three questions for us to answer regarding tlie motion picture. First : Why is it that the pictures seem continuous when as a matter of fact the screen is in total darkness more than thirty times a second? Then the second question is : Why do we get the impression of motion from these pictures which in reality are absolutely motionless? And, third: Why do the pictures have the appearance of depth when in reality they extend only to the right and left, and up and down, and do not possess any objective third dimension or depth? It is to the eye that the motion picture makes its first appeal. And since it is through vision that the apparent motion is perceived it will be necessary for us to take up first of all some phases of the structure and function of the eye as a basis for our understanding of the movies. The human eye is a miniature camera, capable of a large variety adjustments. The eye is wonderfully responsive and automatically so, to the slightest change in light, color or position. But it is not without its defects and shortcomings even in so-called normal eyes. It is by the capitalization of some of these peculiarities, which almost amount to defects, that the movies are made possible. Just behind the pupil of the eye is a small crystal line lens that automatically adjusts • Reprint from cientific Monthly." itself to different distances and conditions of \ ision. The eye thus differs from all other cameras in being self-focusing. No light can enter the human eye except through the lens, since the remainder of the eye forms a light-proof box. The rays of light which pass through this lens into the eye are focused upon the inner surface of the eyeball. This is covered with a layer of highly specialized nervous substance which is acted upon by changes caused by the light. This specialized layer is called the retina and corresponds to the sensitive film or plate in the ordinary camera. In the camera the momentary exposure of light causes a chemical change on the sensitized surface of the film. But before the picture can be brought into view further chemical changes must be effected by the photographer in the processes of development and fixation. Not so with this marvelous human camera. Although vision is essentially momentary in character, due to the continual movement of the eye itself, exposure follows exposure and chemical change follows upon chemical change. There is not time to call in the photographer to develop and fix the pictures after each exposure. Indeed, there is no need. Nature has provided the human camera with a chemical substance sensitive to light which automatically renews itself. This material is called rhodopsin, or visual purple, from its appearance in freshly dissected eyes. This visual purple permeates the entire retinal structure and is probably the keystone to vision. Development and Fixation in Human Camera The development and fixation in the human camera takes place mainly outside the eye. This occurs principally in the brain, to which the eyes are connected by a direct nervous pathway. The retina of the eye is the outpost of the brain, but the nervous material in the retina is not affected directly by the rays of light focused upon it by the crystalline lens. There is an interesting bit of experimental evidence which demonstrates this beyond doubt. Retinas which have been washed free from all chemicals which might permeate the network of nervous fibres have been used for experimentation. It has been found that in order to stimulate this purely nervous structure of the eye directly the light must be so strong as practically to destroy these nervous elements. And still it is a matter for common observation that we can see, that is our retinas are stimulated by lights of weak intensity. The only explanation is the one already suggested. The light acts first upon some photochemical substance which bathes the retina, and the changed chemical composition which the light waves bring about stimulates the nervous parts of the retina. Just what this substance is remains an open question. There is some evidence to indicate that it is not the visual purple. For example, Kuhne found that through continued exposure to light the visual purple in a frog's eye was completely bleached. Still the frog reacted to light and changes in light in a practically normal manner after this thorough bleaching had taken place. Function of Visual Purple of Eye The visual purple is probably the chemical medium for the adaptation of the eye to light or dark illumination. In passing from the open air into the darkened motion picture theatre it takes some time for one's eyes to " get used to the dark." This is technically known as adaptation, and its chemical basis in the eye is the visual purple. This same substance may have a prominent part in the general vision, or another still undiscovered chemical substance may be the basis for vision. At any rate, vision is primarily photochemical. Without the intervention of some photo-chemical material the energy which we call light has no ordinary effect upon the eye. The light which is focused upon the retina by the lens alters the arrangement of the molecules in the photo-chemical material; the energy which we call light has no ordinary effect upon the eye. The light which is focused upon the retina by the lens alters the arrangement of the molecules in the photo-chemical substance. This changed chemical condition stimulates the nervous endings in the retina and these carry their impulses to the brair where they ar« developed (perceived) and fixed (remembered ) . This photo-chemical structure in the retina of the eye is not only the keystone in ordinary vision; it is through some of its properties that the motion picture is made possible. We will now turn our attention to those properties (Contitiued on page 269G) Front of recently completed Warner Brother's Studio in Los Angeles