Mr, W. Hardie's Description of a New Pseudoscope. 443 



Ist. It exhibits the pseudoscopic image either reversed, or in 

 its true aspect, each of these appearances being instantaneously 

 changeable into the other at pleasure. This change is effected 

 by the alternate removal and replacement of the mirrors a, b 

 (Plate VI. fig. 1). When these are removed, the visual rays of 

 the tvro eyes are transposed ; and being twice reflected, the image 

 of course is not reversed. When they are replaced, the rays are 

 not transposed ; but being now thrice reflected, the image is 

 reversed. In both cases the pseudoscopic phsenomena are exhi- 

 bited, but not equally well in cases where the mode in which the 

 object is illuminated is unfavourable, namely, where a side-light 

 occasions corresponding shading. In objects thus illuminated, 

 the conversions of relief are more easily seen with the reversing 

 arrangement than with the other. This seems to arise from the 

 reversed position of the shading corresponding in some degree 

 with the converse form suggested by the instrument, while the 

 unaltered position of it in the other case so strongly contradicts the 

 suggested idea that the illusion is destroyed. A strong side-light, 

 however, except in the case of simple rounded forms, such as the 

 sphere, cylinder, &c., generally overpowers the effect even of the 

 reversing arrangement. 



2nd. By another arrangement of the mirrors, «, b being 

 removed, and c and d turned upon hinges into the position shown 

 in fig. 2, a number of new and very strange phsenomena are 

 displayed. The most striking among these may be generally 

 described as an apparent exaggeration of the depth of space. It 

 is exactly the reverse of the conversions produced by the original 

 pseudoscope. Every prominence seems heightened, every depres- 

 sion deepened, and the space which separates any two objects 

 placed one behind the other appears increased. As examples of 

 these effects I may instance the following : — A round ball seems 

 as if drawn out into an egg-shaped body with the end pointing 

 towards the observer. A piece of money presented with its face 

 towards the observer appears very considerably thicker than it 

 really is ; but when turned round so as to be viewed edgeways, 

 it resumes its natural thickness, and at the same time stretches 

 itself out into an oval medal with its length in the direction of 

 vision. A common wine-glass looked into perpendicularly seems 

 a very deep ale-glass, and an ordinary tumbler viewed in the 

 same manner assumes the appearance of one of those tall glasses 

 used for effervescing drinks. The open hand with the fingers 

 slightly separated appears, if viewed sideways, of a most unna- 

 tural breadth, the intervals between the fingers being correspond- 

 ingly magnified. The nose and projecting features of a person^s 

 face stand out with additional prominence; yet, strange to say, 



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