Motography (Apr-Dec 1911)

April, 1911. MOTOGRAPHY 17 Stereoscopic Projection and ^Alabastra By A. J. Steelkammer STEREOSCOPIC projection, that ignis fatuus pursued spasmodically by inventors since projection and stereoscopy first were known, is again to the fore, encouraged by the broadened powers of modern science. It is the application of a stereoscopic image to a screen that so baffles most investigators. The principles of stereoscopy are not in themselves obscure, and attempts to adapt them to projection were related by La Nature in 1890 or earlier. The celebrated philosopher Bacon, -the founder of the experimental method, claimed that we see better with one eye than we do with two, because the attention is more concentrated and becomes profunder. "On looking in a mirror," says he, "we may observe that, if we shut one eye, the pupil of the other dilates." To this question: "But why, then, have we two eyes?" he responds : "In order that one may remain if the other gets injured." Despite the reasoning of the learned philosopher, we may be permitted to believe that the reason that we have two eyes is for seeing better and especially for perceiving the effects of perspective and the relief of objects. We have no intention of setting forth here the theory of binocular vision ; one simple experiment will permit any one to see that the real place of an object is poorly estimated with one eye. Seated before a desk, pen in hand, suddenly close one eye, and, at the same time, stretch out the arm in order to dip the pen in the inkstand ; you will fail nine times out of ten. It is not in one day that the effects of binocular vision have been established, for the ancients made many observations on the subject. It was in 1593 that the celebrated Italian physicist Porta was the first to give an accurate figure of two images seen by each eye separately, but he devised no apparatus that permitted of reconstituting the relief on looking at them. Those savants who, after him, occupied themselves with the question, treated it no further than from a theoretical point of view. It was not till 1838 that the English physicist Wheatstone constructed the first stereoscopic apparatus permitting of seeing the relief on examining simultaneously with each of the eyes two different images of an object, one having the perspective that the right eye perceives, and the Old Method of Sterecoscopic Projection with From a Wood Cut. other that which the left eye perceives simultaneously. This apparatus is described in almost all treatises on physics. We may merely recall the fact that it operated by reflection, that is to say, the two images were seen through the intermedium of two mirrors making an angle of 45 degrees. The instrument was very cumbersome and not very practical. Another English physicist, David Brewster, in 1844 devised the stereoscope that we all know ; but, what is a curious thing, he could not succeed in having it constructed in England, where it was not at first appreciated. It was not till 1850 that he brought it to Paris, where it was constructed by Mr. Soleil and his son-in-law Duboscq. Abbot Moigno and the two celebrated opticians succeeded, not without some difficulty, in having it examined by the savants ; but, at the great exposition of 1851, it was remarked by the Queen of England, and from this moment Messrs. Soleil and Duboscq succeeded with difficulty only in satisfying the numerous orders that came from all parts. As photography permitted of easily making identical images, but with different perspective, it contributed greatly to the dissemination of the apparatus. The stereoscope, such as we know it, presents the inconvenience of being incapable of use by more than one person at once. Several inventors have endeavored to render the stereoscopic images visible to several spectators at the same time. In 1858, Mr. Claudet conceived the idea of projecting the two stereoscopic images upon ground glass in superposing them. The relief was seen, it appears, but we cannot very well explain why; the idea, however, had no outcome, because the image, being quite small, could be observed only by but three or four persons at once. It was Mr. D'Almeida, a French physicist, who toward the same epoch solved the problem in a most admirable manner, and we cannot explain why his process (that required no special apparatus) fell into the desuetude from which Mr. Mob teni rescued it and obtained much success. The impression of the relief appears when each eye sees that one of the two images which presents the perspective which it would perceive if it saw the real object. If we take two transp a)r e n t stereoscopic images and Red and Green Glasses.