joumilS^ri^a ] Royal Microscopical Society. 275 



divided and reflected horizontally to the eyes through two equally 

 inclined eye-pieces. 



It was shown that, if the angulated surface was cut into the 

 lens, the image was pseudoscopical ; but that if the reflectors were 

 made by cutting off the lens, the right eye would receive the left 

 image, and vice versa, the result being a stereoscopic view. 



Now this contrivance, although optically qualified to give equal 

 binocular pictures, had certain disadvantages that prevented me 

 making further use of it, the greatest of these being, that the body- 

 tubes must be horizontal, while the objective is vertical, which is 

 rather unsightly and quite contrary to practice. 



The paper will be found at length in No. 9 of Journal of the 

 Quekett Club, and was noticed in the Monthly Journal of this 

 Society, No. III., March 1, 1869. 



The instrument I am now about to describe is on a difierent 

 principle to the foregoing, and is my latest invention ; my first view 

 through the first one completed, dating 19th May, 1869, and I 

 have since been employed in perfecting the mechanics of the 

 design. 



Suppose, for illustration, we had a complete and well-appointed 

 achromatic microscope, and we were to make a clean vertical section 

 through the centre of the optical parts and their supporting brass- 

 work. 



Now, although completely dissevered, we could see through it 

 just as well as before its division. But the division of the eye-piece 

 being near the eye would be visible, and therefore might be left un- 

 divided, as it is mainly with the object-glass that we have to deal. 



Now, being in possession of an imperceptibly bisected instru- 

 ment, if we consider each half as the radius of a circle tvhose centre 

 is the focus of the object-glass, we may, by separating the halves of 

 the body at the upper end to the distance between the eyes and adding 

 two eye-pieces, observe binocularly any object that ivas in focus when 

 closed as a single body. And here we get an opportunity of proving 

 the truth of the opinions of Harris, Goring, and Brewster, previously 

 quoted. 



The binocular vision here provided is strictly natural, both 

 eyes being used under exactly the same conditions as when ex- 

 amining an object unassisted at the distance of distinct natm-al 

 vision, for the two converging optic axes are directed to the same 

 object, and have the same assistance as to magnifying power and 

 illumination, and the rehef presented by an object of solidity must 

 be absolute for quantity and correctness. 



The indirectness of the path of the light forming the second image 

 in the Prism Binocular, before referred to, prevents the use of high 

 powers, because the errors become too sensible to be disregarded. 



But in the bisected arrangement, the highest power attainable 



T 2 



