l°S.-nil Srim'] I^oyal Microsco'pical Society. 277 



The illumination of opaque objects is effected by any of the 

 well-known means for that purpose; but I prefer to use a side 

 reflector, because of the light and shade giving the best effect. 



For the illumination of transparent objects, an equilateral prism 

 has one of its sides worked into two facets at such an angle as to 

 throw the light from its internal reflecting surface in the direction of 

 the halves of the object-glass, when placed under the stage. 



The definition of an object with this angulated prism is far 

 superior to that given by an illuminating lens. For use by lamp- 

 light the incident surface of the prism is made convex, and the light 

 placed in the focus of its convexity becomes parallel before faUing 

 on the reflecting surface. The same effect may be produced by a 

 condenser before the lamp. 



These microscopes claim to give a truthfully stereoscopic view 

 of both opaque and transparent objects, by the employment of two 

 direct and equal pencils of light, having origin at the object, and 

 giving vision to each eye, under precisely similar conditions, and 

 whose images being equal in illumination and definition, can but 

 give a magnified presentment of an object in all its dimensions when 

 blended by two eyes. 



I believe that this Binocular Microscope will be found to give 

 us the power of making perfect Stereographs of the most minute 

 objects, and when these shall be viewed in the common stereoscope 

 a complete idea of form, proportion, and solidity, will be arrived at 

 by mere inspection : and I have thought that the apphcation of 

 this principle might lessen the fatigue of astronomical observations, 

 and increase the perception of detail, by the penetration of the gaze 

 of two eyes over that of one alone, 



I had the honour of exhibiting the Instruments, Models, Draw- 

 ings, &c., at the Soiree of the Koyal Society for this year, held 

 23rcl April, at BurHngton House, when many gentlemen expressed 

 high opinions of the value of the principle. Professor Tyndall de- 

 clared the depth of the transparent views to be " wonderfully beau- 

 tiful," and those of the opaque objects to be "perfectly stereo- 

 scopic." 



APPENDIX. 



Illustrations of Construction. 

 In order to show the very general interest taken in binocular vision 

 I here insert an extract from the ' British and Foreign Mechanic ' of 

 Feb. 5th, 1870. It will serve our pm-pose in other ways, as it is weU 

 illustrated, and was published unsolicited : — 



" Improvements in Binocular and Stereoscopic Microscopes. 

 " Our readers have many times forwarded queries to us relating to 

 the construction of the binocular microscope ; so we think it necessary 



