175 



Memoir on a New Form of Binocular Microscope. By 



Samuel Holmes. 



(Read by Mr. George, January 22nd, 18 69 J 



Some time previous to the introduction of the Binocular Microscope 

 by Mr. Wenham — I think in the year 1858 — I had been engaged 

 with the subject of a stereoscopic microscope myself and being 

 familiar with Mr. Wenham's former experiments, I came to the 

 conclusion that some use might be made of the property of total 

 reflexion from a glass second surface, instead of using any refracting 

 arrangement. 



I now pi'opose to describe to the meeting an incomplete experi- 

 ment on this basis, which I ceased to prosecute on the appearance 

 of Mr. Wenham's beautiful Prism Binocular. 



Now although this experiment of mine has been so long laid 

 aside — there was no Quekett Club in those days — I am still of 

 opinion that the scheme is worthy of further trial, and I have been 

 induced to bring the matter before the meeting by reading the 

 excellent remarks on the requirements of Binocular Vision in the 

 reported speech of Mr. Durham. 



In this microscope I propose to divide the light from the object 

 glass into two portions, and to direct one half into each eye through 

 the medium of two reflectors and two eye-pieces, so as to gain a 

 more perfect knowledge of the structure observed, while such 

 observation shall be less fatiguing, being conducted by two eyes 

 whose optical axes are equally inclined. The object glass consists 

 of an hemispherical plano-convex lens, the plane side of which is 

 either ground off or ground into, two facets, representing the angle 

 of stereoscopic vision. This lens is placed over the object with its 

 obtuse, or its re-entrant angle — according to which form is used — of 

 its face, at an angle of 45 '^ to the perpendicular, in which direction 

 the rays from the object reach it, to be divided and reflected 

 horizontally to the eyes through two converging eye-pieces. 



There is thus, first a plano-convex lens, to receive and amplify 

 the object; secondly two plane mirrors, for reflecting two distinct 

 and angular half-field views of the object stereoscopically, and lastly 

 a secondary plano-convex lens for still further increasing the ap- 



