156 ANNUAL OF SCIENTIFIC DISCOVERY. 



ground giass placed before an ordinary stereoscope at the distance of the 

 focus of its semi-lenses, the slide being strongly lighted, and the eye seeing 

 no other light than that of the picture on the ground glass. The whole 

 being nothing more than a camera having had its lens cut in two parts, and 

 the two halves sufficiently separated to produce at the focus the coincidence 

 of the two opposite sides of the stereoscopic slide placed before the camera. 



The Stenomonoscope. At a subsequent meeting of the Royal Society, M. 

 Claudet presented a new optical instrument of his invention, called the Stc- 

 rcomonoscopc, by which, as its name implies, a single picture produces the 

 stereoscopic illusion. In the centre of a large black screen there is a space 

 filled with a square of ground glass, upon which, by some light managed 

 behind the screen, is thrown a magnified photographic image representing a 

 landscape, a portrait, or any other object. When w r e look naturally at that 

 picture, with the two eyes, without the help of any optical instrument, an 

 extraordinary phenomenon takes place : we see the picture in perfect relief, as 

 when, we look at two different pictures through a stereoscope. It is not nec- 

 essary to be at a fixed distance from the picture; it may be examined as 

 well at ten feet as at one foot, as an ordinary picture, Avithout the least 

 fatigue to the eyes. Although considerably enlarged by the instrument 

 itself, we may magnify the picture still more by using large convex lenses ; 

 and two or three persons at once can examine it with the greatest case, being 

 able, while looking, to exchange any remarks, or express the sensations sug- 

 gested by the picture, an advantage which is denied by the use of the 

 common stereoscope. By this remarkable discovery, M. Claudet has solved 

 a problem which has always been considered as an impossibility by scien- 

 tific men, for the stercomonoscope, by its very name, must sound like a 

 paradox to the ears of all those who are versed in the knowledge of the 

 principles of binocular vision, until they have had the opportunity of repeat- 

 ing the experiments by which the author has found a new fact which they 

 had not noticed or explained befoi'e. This new fact is, that the image on 

 the ground glass of the camera-obscura produces the illusion of relief. But 

 the phenomenon does not take place if the image is received on paper. 

 When the medium is ground glass, the rays refracted by the various points 

 of the lens upon that surface are only visible when they arc incident in a 

 line coinciding with the optic axes. So that the rays emerging from the 

 ground glass, and entering the right eye, are only those which have been 

 refracted obliquely in the same direction, by the left side of the object-glass ; 

 and those entering the left eye arc only those which are refracted by the 

 right side of the object-glass; consequently, both eyes have a different vie\v 

 and perspective of the object represented on the ground glass, and the single 

 image is, in point of fact, the result of two images, each only visible to one 

 eye, and invisible to the other. This is the main point of M. Claudet's dis- 

 covery, which cannot be fully understood Avithout reading the preceding 

 paper, and AA r ithout repeating the experiments described in that paper. The 

 stcreomonoscope is founded on the same principles ; it is nothing more than 

 a camera-obscura, before which are placed two images of a stereoscopic 

 slide, and by means of tAVO object-glasses, sufficiently separated, the two 

 images are refracted on the same space, at the focus of the camera-obscura 

 on the ground glass, where they coincide. By the same hnvs AVC have 

 alluded to before, the right picture is seen only by the left eye, and the left 

 picture by the right eye; so that, although only one picture appears repre- 

 sented on the ground glass, each eye sees on the same spot a different pie- 



