On Orfhoscopic and Fseudoscopic Effects. By Prof. E. Ahhe. 205 



displaced to the left hand (and the more distant planes to 

 the right hand) in opposition to the projection of the same 

 object for the left eye; pseudoscopic vision results from 

 projections of an inverse character. 



Stereoscopic effect in the binocular Microscope arises 

 from an opposite perspective character of images vrhich are 

 projected by incident pencils of different inclination at the 

 preparation — i.e. which are delineated by different parts of 

 the objective's clear aperture. 



These premises being conceded, the strict and direct way for 

 discussing the phenomenon of stereoscopic vision in the Micro- 

 scope must necessarily start from a consideration of the three- 

 dimensional image which is projected to the observer's eye by 

 the total Microscope. For in microscopic vision we do not see the 

 object itself, as in direct vision with the naked eye ; we see the 

 virtual image only, which is finally delineated by the ocular, and 

 is a solid image with a certain amount of depth when the object is 

 a solid object. This solid image — and not the microscopical object 

 — is placed in the binocular Microscope under circumstances similar 

 to those of common objects in ordinary binocular vision. Therefore 

 the perspective projections of this image ought to be compared 

 to the projections of solid objects in ordinary vision, in respect to 

 which the criteria of orthoscopic and pseudoscopic vision have been 

 defined. 



With this in view, let a, h, in Fig. 37, represent two different 

 planes of a solid object, to which a Microscope has been focussed, and 

 E, L two incident rays, or pencils, departing from the point o with 

 opposite obliquity and transmitted through opposite portions of 

 the objective's clear aperture. Neglecting all intermediate elements 

 of the optical system, and considering only the final virtual image 

 of the object which is delineated by the total Microscope within 

 the range of distinct vision, let a* and &* indicate those plane 

 images which are conjugate to the planes a and h of the object, and 

 r, I the final emergent pencils (crossing at the point o* conjugate 

 to o) which result from the incident pencils E, L, and are admitted 

 to the pupil of an observer's eye at E. 



The directions r, I now indicate the difference of perspective 

 which produces the effect of solidity in the image. Whenever this 

 image is depicted by one of the incident pencils only, the other 

 being shut off from the pupil, the consecutive layers a*, h* (and all 

 intermediate ones) are viewed either along the direction r, or along 

 the direction I. Point o* of the plane a* is now seen projected 

 either to point p* or to point q* of the plane h*, and opposite 

 parallactic displacement of consecutive planes is thus introduced 

 into these partial images. 



Ser. 2.— Vol. I. Q 



