On OrtJwscopic and Pseudoscojnc Effects. Bij Prof. E. Able. 207 



A glance at the diagram will at once show that a parallactic 

 displacement of the upper plane of the image to the left hand 

 must occur when this image is seen by means of the pencil r, 

 which is incHned to the right hand, and vice versa. The pencil *• 

 represents the right portion, and I the left portion of the total cone 

 of emergent rays, which would be transmitted to the eye, if the full 

 aperture of the objective were active. Considering now the 

 criterion of orthoscopic vision with the naked eye, which has been 

 indicated above, the conclusion must be : right-eye perspective of 

 the solid image is always obtained from the right-hand portion of 

 the emergent pencils, left-eye perspective from the left-hand portion ; 

 and it is quite immaterial, as regards this residt, which piortion of 

 the emergent rays is admitted hy the right or the left part of the 

 objective. 



Hitherto the perspective character of projections by pencils of 

 opposite inclination has been defined in respect to the three- 

 dimensional image which is seen like a real object with the naked 

 eye. For defining now the character of the same projections in 

 respect to the object, it is sufficient to take into account a general 

 proposition of geometrical optics, which shows : — The axial sequence 

 of the layers in an image is always conformable (and never the 

 opposite) to the sequence of the conjugate layers in the object, 

 whatever may be the composition of the optical system, provided 

 the layers in question be delineated in a continuous manner (or 

 what is an equivalent expression — at one and the same side of the 

 principal focus of the system). As this condition is always fulfilled 

 under the circumstances of microscopic vision, the final image of the 

 Microscope is always erect in respect to depth, whether it be erect 

 or inverted or semi-inverted in respect to the lateral dimensions. 

 Now the character of solid vision (orthoscopic or pseudoscopic) 



if the consecutive planes are very close together (and M = N). Denoting by 

 u and u* the obliquity of a given ray, or pencil, at the object and at the image, 

 we have, provided the system is aplaiuitk in respect to the conjugate points in 

 consideration, 



1. 



The terms of the left-hand side of this proportion are approximate expressions of 

 the relative parallactic displacement of the consecutive planes in the projection of 

 the solid object and of the solid image along the oblique ray in question. It is 

 thus seen that these displacements retain approximately the ratio of the amplifica- 

 tion, the loss of obliquity at the image being just balanced by the extra increase 

 of the axial distances there. 



Q 2 



