318 



Mr. A. Stroll. 



[Apr. I, 



same must naturally be of limited dimensions ; and though viewed 

 through magnifying lenses, the images of the objects are presented 

 to the eye on a scale far below the size of their originals. 



It has therefore occurred to me, that if the magnified image of a 

 photograph projected on a screen by the optical lantern could be made 

 stereoscopic, a still greater resemblance to the original might be 

 obtained. 



With a view of producing such an effect, I have constructed the 

 apparatus I will now describe, which is, however, not intended to 

 enable a large number of persons to see the projected pictures at the 

 same time, as in the case of dissolving views, but is at present limited 

 to the use of two persons simultaneously. It could, however, be 

 easily constructed so as to be available for a greater number. 



The principle of the arrangement depends on the well-known 

 effects of the persistence of vision; revolving disks are employed for 

 alternately obscuring two pictures, projected on a screen in the same 

 place, and at the same time interfering with the view of the observer 

 in such a manner that only one picture is seen by the observers' right 

 eyes, and the other by the left eyes. 



Two optical lanterns are placed side by side, as for dissolving views. 

 Two transparencies, photographed in the same manner, as if intended 

 for an ordinary stereoscope, are placed one in each lantern, and pro- 

 jected on a screen in such a position that they overlap each other as 

 nearly as possible. The picture which is intended to be seen by the 

 right eye may be placed in the right hand lantern, and the other in 

 the left. 



Supported by suitable framework, and in the front of the two 

 lenses of the lanterns, is a revolving disk, portions of which are cut 

 away, so that during its revolutions it obscures the light of each 

 lantern alternately, or in other words, so that only one picture at a 

 time is thrown on the screen. A continuous change from one picture 

 to the other is thus obtained. 



In the same framework, and in convenient positions for the observers, 

 two pairs of eye-holes are provided, one pair on either side of the 

 apparatus. Behind each pair is also a rotating disk, and these disks 

 are connected by suitable wheel- work or driving bands with the one 

 previously mentioned, in such a way that the three disks rotate 

 together, and at the same rate. The two last-named disks are also so 

 cut that they will obstruct the view through the right and the left 

 eye-holes alternately. 



Finally the connexion between the three disks has to be so arranged 

 that the time of obscuring the view of the observers' right eyes or 

 left eyes shall coincide with the time when the light is shut off from 

 the right or left lens of the lanterns respectively. 



It is obvious that by this arrangement the left eyes can only see the 



