255 THE MICROSCOPE AND ITS REVELATIONS. 



scale the solid form of the object from which they were taken. What is 

 needed, therefore, to give the true Stereoscopic power to the Microscope, 

 is a means of so bisecting the cone of rays transmitted by the objective, 

 that of its two lateral halves one shall be transmitted to the right and the 

 other to the left eye. If, however, the image thus formed by the right 

 half of the objective of a Compound Microscope were seen by the right 

 eye, and that formed by the left half were seen by the left eye, the result- 

 ant conception would be not stereoscopic but pseudoscopic; the projecting 

 parts being made to appear receding, and vice versa. The reason of this 

 is that as the Microscope itself reverses the picture ( 26), the rays pro- 

 ceeding 'through the right and the left hand halves of the objective must 

 be made to cross to the left and the right eyes respectively, in order to 

 correspond with the direct view of the object from the two sides; for if 

 this second reversal does not take place, the effect of the first reversal of 

 the images produced by the Microscope exactly corresponds with that 

 produced by the 'crossing ' of the pictures in the Stereoscope, or by that 

 reversal of the two perspective projections formed direct from the object, 

 which is effected by the Pseudoscope ( 31). It was from a want of due 

 appreciation of this principle (the truth of which can now be practically 

 demonstrated, 38), that the earlier attempts at producing a Stereosco- 

 pic Binocular Microscope tended rather to produe a ' pseudoscopic con- 

 version ' of the objects viewed by it, than to represent them in their true 

 relief 



Fro. 18. 



Arrangement of Prisms in Nachet's Stereoscopic 

 Binocular Microscope. 



Nachet's Stereoscopic Binoculf r. 



33. Nacliefs Stereoscopic Binocular. The first really satisfactory 

 solution of the problem was that worked out by MM. Nachet; whose 

 original Binocular was constructed on the method shown in F ; g. 17. 

 The cone of rays issuing from the back lens of the objective me3ts- 

 the flat surface of a prism (p) placed above it, who section is an equilit- 



