Steoscope is an instrument which, from two pictures taken at different angles, presents to our view objects at a short distance in the solid form. Common pictures have a flat, dead appearance; stereoscopic pictures stand out in life-like relief. The reason ol this is that, with the stereoscope, each of oui eyes obtains a somewhat different view of the object, and they find the true form of it ou of the two perpective views or pictures taken at different points. If, however, the distance from we view the pictures in the stereoscope is considerable, the eyes are too slow in their action to enable the observer to form a correct. idea of the distance and the form of the obj)3ct represented, unless some very favoring ciwumstances oflight and shade assist in doing aoi. Ranges of distant mountains generally appear to the n d eye like perpendicular walls attached to the firmament. In the stereoscope, it is possible to combine two perspective views of a landscape taken from two different points iently distant so as to give the ob- erver a correct idea of the real or true forms smbraced in the views. A stereoscopic pic-ure, therefore, conveys a more perfect repre-lentation of a landscape than an observation made with the naked eye. It is only by ;hanging positions, and thereby obtaining different perspective views of a landscape, and Dy comparing these views, that an observer is enabled to perfect his observations, and to obtain something like a correct idea of the forms of the objects embracing the scene. If the observer could take different views of a landscape at the same moment, the scene presented to his vision would be charming and ife-like. But this he cannot do, neither can t be done with the common stereoscope for distant objects ; but in Dingier's Polytechnic Journal, published at Augsburg, Germany, it is stated that this is accomplished by a simple instrument called the "tele-stereoscope," recently invented by M. Helmholz. It consists simply of a smooth board, four feet long, on each end of which a looking glass is fastened perpendicular to its plane, and making an angle of 45, with a line drawn longitudinally through the center of the board. In the middle of the board, two other smaller looking-glasses are fastened parallel to the first two, and so close together as to enable the observer to look at once with an eye into each. If it is desirable to magnify the object, an opera glass or spectacle lens may be inserted between the eye and the looking-glasses. By these means the right eye sees the landscape as it appears in the looking-glass at the right end of the board, while the left eye sees it as it appears on the looking-glass at the left end. The distance of the observer's eyes is increased by these means from about three inches (the common distance) to four feet, and he thereby obtains a view which as far surpasses stereoscopic photographs as an oil painting excels an engraving. The journal referred to also states that objects distant from one to two miles appear correct in the back ground, and nearer objects very perfect, particularly trees, the limbs and branches of which are distinctly separated, and the whole landscape stands out solid and beautiful.
This article was originally published with the title "The Tele-Stereoscope" in Scientific American 13, 19, 149 (January 1858)