45 



Binoculars. 



By E. M. Nelson, F.R.M.S. 



(Mead May 20th, 1S92.) 



There has been a great deal of unnecessary confasion caused 

 by Prof. Abbe's unwarranted attack on the late Dr. Carpenter's 

 views with regard to the stereoscopic binocular. 



Dr. Carpenter stated that orthostereoscopic effects can only be 

 seen in an inverting microscope,* when there is a "cross-over," 

 and that, if there is no " cross-over," the image will be pseudo- 

 stereoscopic ; but with an erect image,t if there is a " cross- 

 over," the image will be pseudostereoscopic, and with no 

 " cross-over," orthostereoscopic. 



Prof. Abbe takes exception to this statement of Dr. Car- 

 penter's ; he puts the above proposition in another form, saying 

 what is practically the very same thing, and of course arriving 

 at the same results ; but Abbe puts it in such a way that, while 

 he appears to say something very different to what Dr. Car- 

 penter says, in effect, however, he does not, and this I hope to 

 clearly demonstrate to you. 



Of the two theories, however, that of Dr. Carpenter's is the 

 more complete. In the first instance, we must divide the sub- 

 ject into two parts : — 



1. The "cross-over" orthostereoscopism and pseudostereo- 

 scopism. 



2. The origin of the dissimilar images. 



The essential point in orthostereoscopic vision with a micro- 

 scope is that " the ordinary view " of objects be maintained. 



* " Inverting microscope." It must be especially borne in mind that an 

 ordinary inverting microscope transposes the image as well as inverts it. 

 The inversion does not affect the question at all; it is the transposition which 

 may or may not accompany the inversion that is the all-important point. 

 I have adhered to the term " inverting microscope '' because the phrase 

 transposing microscope might lead one to suppose that it was not the 

 ordinary instrument that was meant. 



t So, too, in an erect image it is the non-transposition that is of import- 

 ance. 



