THE STEREOSCOPE
An Old Favorite Comes Back in Modern Form
A MONG THE CHILDHOOD MEMORIES of many of us linger the wonders of stereoscopy in which two apparently similar photographs, mounted side by side, miraculously acquired three dimensions when looked at through the stereoscope. You may have wondered why the march of time had left this fascinating device behind. Had you been in Hanover during February and March of this year, you would have discovered not only that the old stereo is still going strong and now appearing in color, but also that many new methods have been evolved. For the spectator's benefit the special Dartmouth exhibition was arranged historically so that he could be nostalgic in the Victorian corner or extremely modern with vectographs and aerial photography.
There have been several new developments in the art of presenting stereoscopic pictures (some of them quite startling) so that it seems desirable to review these developments and especially to consider the possibilities of the applications of new techniques and materials.
We have TWO eyes the better to see with. Why two eyes?
In performing our daily chores, in getting about from one place to another, working, avoiding pain and seeking pleasure we continually make judgments concerning space, form, and relative distance. Hold your finger up at arm's length; if you look at it first with one eye and then the other, you will note that the finger appears to move sideways with respect to the object behind it, or that the objects appear to move sideways with respect to your finger. This shows that the two pictures in our eyes are slightly different, due to their difference in position. The differences in the two pictures are very slight, but through having grown up with them and made associations between appearance and tactual experience we learn to interpret the differences in terms of difference in distance away from us, shape, and form. Naturally the strongest impression of depth is closest to the observer.
While it is true that the pictures in the two eyes and their interpretation into one picture with depth is not the only source of clues on which to base judgments of space, form and difference in distance away, it is the most important one. With one eye alone an observant person can judge depth quite accurately from such clues as known size, shading and shadows, perspective, overlapping and relative motion. The latter is the most important monocular clue, which explains why a oneeyed man seems to have so little difficulty in getting around in traffic.
In about 1840 an Englishman named Elliott invented what was probably the first stereoscopic viewer, consisting of a box with two holes in one end and one hole in the other. The size of the holes and the shape of the box were such that one saw, on looking through it, a drawing for the right eye placed to the left and another drawing for the left eye placed to the right, the sight lines crossing over in the box and being framed by the hole in the box. Soon after this, Wheatstone invented a 'scope using mirrors, and Brewster invented one using prisms, and for a while these two distinguished gentlemen wrote back and forth in the London Philosophical Transactions calling each other names and arguing as to who had invented what and when, and which was the better stereoscopic viewer.
Thus some of the fundamentals of stereoscopic vision had been worked out before photography really got going, with the result that practically the second photograph ever taken was taken stereoscopically; and the developments in photography have been applied to stereoscopic work soon after their invention. The progress of the two have, with few exceptions, been parallel.
Since then some stereoscopists have worked out improvements in the design of the viewing devices, either simplifying them or reducing the distortions inherent in the early ones. Others have contributed entirely new techniques such as the analglyph which uses color to do the separating; or projection with polarized light, which, though invented about 1890, became practical much later when extended sheets of polarizing film were made; or the idea of showing the pictures alternately on the screen and viewing them through a shutter synchronized with that on the projector.
These systems, and some others, solved many of the problems that existed. But now comes the vectograph, which simultaneously solves most of the problems inherent in the presentation of three-dimensional pictures. This is probably the most significant contribution not only to the art of stereoscopy but also to the art of photography in the past twenty-five years. While -several new photographic and other tricks can be done with this distinctively American technique, it lends itself particularly well to stereoscopy. Some of the problems the vectograph is now competently solving are war secrets, but we can discuss others. Much of the available material is being used for camouflage detection, bomb damage evaluation and so on, all in connection with aerial photography. Some material is available for educational purposes in connection with war-training, in which we should be particularly interested.
In the Navy V-12 training program which is now being carried on at Dartmouth, the work that the trainees do is of a rather intensive sort; they are required to absorb, digest and be able to use a larger number of new concepts per hour than ever before, many of which are quite foreign to them, and for the grasping and use of which they may have little aptitude.
Picturing a solid object or realizing the spatial relations of objects from drawings is hard enough for a trained person, but when at the same time a trainee has to learn the language with which these "projections" are described and to visualize from them, he frequently becomes swamped. The use of some well-chosen stereoscopic drawings to supplement the regular two-dimensional ones has been demonstrated to be of considerable assistance in getting space-concepts across to the student who has trouble in visualizing from the regular drawings alone.
Thus, exciting possibilities are opened up for improving the teaching of those courses in which concepts involving threedimensional spatial relationships are important. Some work had already been done on this before the war; when this happened the knowledge thus gained and the new techniques were immediately applied to courses important in war-training. The drawings, and in some cases combinations of drawings and photographs, have been made for the propositions in solid geometry, some for those in spherical trigonometry, for navigation and celestial navigation, engineering drawing and descriptive geometry and also a few in physics, chemistry, medicine, engineering, and various other subjects. Other sets for more restricted use in more advanced training are undoubtedly being used; about these we may expect to learn more after the war.
Professor C. P. Lathrop and the writer arranged an exhibition in the Carpenter Art Galleries in February and March of this year to show some of the things we have been discussing above. Many stereographs which illustrated stages in the development of stereoscopy and American history were hung on the walls, and Holmes-type stereoviewers were adapted so that they could be used to view them. In one corner was a set of Victorian vintage arranged by George Schoenhut of The Dartmouth Players. Among the archives were found some stereo negatives taken about 1860-1870 (the time of the wetplate). Those which illustrated interesting aspects of Hanover and life in Hanover of that period were printed and, together with some more modern views of the town (some being in color), made a "Hanover Room."
Paul Sample, our well-known Artist-in-Residence, kindly made some drawings and paintings which showed the devices used by the artist to suggest three dimensions in two-dimensional pictures.
Also shown in the exhibition were some of the slides illustrating the applications of three-dimensional pictures to courses such as engineering drawing, descriptive geometry, etc. Of interest to the men of the V-12 map-reading course were vectographs made from aerial photographs, both vertical and oblique.
When the Commanding Officer of the Dartmouth V-12 Unit saw this exhibition, he wrote to the director of V-12 training in the First Naval District about it, especially recommending that men from the other V-12 programs see it. He also asked that a memorandum be prepared and sent to the appropriate persons in Washington.
When the war is over great advances will be made along the lines of three-dimensional pictures for all uses, including educational visual aids, as the techniques now largely or wholly devoted to the war effort become available for civilian uses.
VICTORIAN CORNER in Dartmouth's recent exhibition tracing the development of the stereoscope from its beginning up to modern use in education and in winning the war.
INSTRUCTOR IN PHYSICS
