Mr. J. Elliot on two new Forms of the Stereoscope. 105 



possession two beautiful binocular photographic landscapes, by 

 Mr. Wilson of Aberdeen. They were not small pictures, such 

 as are usually made for the stereoscope, but were each some- 

 where about 12 or 13 inches long and 10 broad. Mr. Waterston 

 had been in the habit of uniting stereoscopic views by the eye 

 alone, without the use of an instrument. He tried the large 

 landscapes in the same way and succeeded in uniting them, but 

 with that picture which is usually the right-hand one placed on 

 the left, and the left-hand one on the right. Having tried to 

 unite the pictures in the same way, but without success, I im- 

 mediately undertook to produce an instrument by which the pui*- 

 pose might be effected, and found the attempt successful. In 

 fact 1 had thought of the same instrument before for uniting 

 small binocular pictures crosswise. That iustiaiment is simple 

 enough. It consists of a wooden frame, like a box open at one 

 end; the two sides (represented by AB and CD in fig. 1) fold 

 together with hinges at A and C, while the front or closed end, 

 A C, has two openings, E and E', at the distance of the two eyes 



from each other. At first these openings were hollow truncated 

 cones, with a small aperture at the narrower end (as in the figure), 

 and fixed to slides by means of which they could be adjusted to 

 the exact distance of the eyes. The object of having the aper- 

 tures so small, was to deprive each eye of its power of detecting 

 distance by means of its own focal adjustment; a power which, 

 it is well known, the eye possesses. I had another pair of slides, 

 however, made with large apertures, and found that they answered 

 nearly as well, and were much more easily used. 



The sides are folded in, so far that the right-hand side entirely 

 hides the right picture, 1", from the right eye, and the left-hand 

 side hides the left picture, P, from the left eye ; while they are 

 made of such a length us to leave each picture wholly seen, and 

 no more, by the alternate eye. The extremities, B and D, of the 

 sides are then distant about two inches from each other for ])ic- 

 tures of the size mentioned. The height of the aperture is also 

 at the same time contracted by a piece of cardboard, or by two 



