48 



E. M. NELSON ON BINOCULARS. 



the various forms of binoculars. Thus let the marginal rays be 

 called mM and the central cC, the left hand portion being 

 in small letters, and the right hand in capitals ; the aperture of 

 the objective (say, the back lens) will be represented by mc CM. 

 When the image is inverted the letters will be inverted thus, rao 

 MC- By this means transposition, cross-over, and inversion 

 will be made clear. 



The following table shows how the rays leaving the objective 

 in the order mc C M emerge at the eye-spots. 



Table showing what portions of the objective image are visible at 

 the eye-spots of various binoculars. 



Left hand marginal ray at back of objective m 



Rigbt „ „ „ „ M 



Left hand central ,, „ c 



Right „ „ „ „ ...... C 



Position of rays at the back of objective mcCM 



When the letters are inverted the image is inverted, other- 

 wise the image is erect. 



Name of Binocular. 



Abbe 



Beck 



Cherubin d'Orleans 



Holmes 



Nachetl 



Nachetll 



Powell 



Stephenson 



Tolles 



Wenham 



Orthostereoscopio. 

 Left eye. i Right eye. 



lAlO 



mc 

 mc 



lAIO 

 lAlO 

 lAlO 



mo 

 mc 



lAlO 



otn 



CM 

 CM 



OttI 



Ota 

 oiu 



OIAI 

 CM 



om 



Pseudostereoscopic. 

 Left eye. Kight eye. 



lAlQora 



oiu 



OIU 



lAlO 



R 



lAlO ow 

 lAlO 



I/MO 

 lAlO 



The following example shows how by my table the effects 

 can be at once traced without the necessity of a diagram when 



