THE STEREOSCOPE AND VISUAL INTERPRETATION 1 85 



Stereoscopic views are made not entirely by the method above 

 described, but by photography. The stereographic camera has two 

 plates and two bull's eyes the interocular distance apart. Both plates 

 are exposed simultaneously. The picture taken by the right camera 

 is mounted on the right side of the stereographic card, and that by the 

 left on the left side. In this way we get all the advantage of details, 

 which by drawing would be impossible. We see as when looking at 

 the scene directly. There is an appearance of reality which cheats 

 the senses with its seeming truth. Through the stereoscope we do not 

 get a miniature image of the object observed, as is often supposed. The 

 six-inch lens of the stereoscope compensates entirely for the six-inch 

 lens of the camera by which the picture was made. The following 

 experiment was made by the author to ascertain this fact: A picture 

 was made of a scene (Madison Square Garden, New York) with the 

 regular stereographic camera. The left picture of the scene was mounted 

 and placed in the left side of the stereoscope. The lens on the right 

 side of the stereoscope was removed so that the right eye was free to 

 view the scene. 1 When the observer stood in the exact position where 

 the picture was taken and looked at the scene (i. e., looking through 

 the stereoscope with the left eye stimulated with the left stereograph, 

 and the right eye free) the two images exactly superposed and the 

 results were the same as when the two eyes were free. 



To show the disparity of the images seen by the two retinae, I give 

 below the stereograph of the girl stretching forward her hands. Notice 

 the position and size of the hands when just looking at the picture as a 

 photograph. The right hand of the left figure is almost in front of the 

 face, whereas in the other figure it is quite to the side. Where is it 

 when the two figures are superimposed ? Notice how much smaller 

 the hands seem when there is stereoscopic effect. By this time the 

 cause of all this will be understood. 



The second picture is one of President Roosevelt standing on a high 

 point. It seems almost level behind him toward the falls, but superpose the 

 two images ! You can now see thousands of feet down into the rugged 

 gorge of the Yosemite. It is indeed wonderful, and one is almost as 



1 That is, the real scene. 



