NACHET S STEREO-PSEUDOSCOPIC BINOCULAR. 35 



Microscope, the entire cone of rays passing uninterruptedly into 

 it ; and third, that the simplicity of its construction renders its 

 derangement almost impossible. * 



28. Stereoscopic Binocular Eye-piece. — An ordinary Microscope 

 may be converted into a Stereoscopic Binocular, by an arrangement of 

 prisms devised by Professor Smith, of Kenyon College, U.S. ; which 

 corresponds in principle with that originally adopted by MM. Nachet 

 (Fig. 17), but is made on a larger scale, and is inserted into the 

 upper part of the body instead of into the lower, so as to divide the 

 pencils of rays near the plane at which they would form the image 

 into two lateral halves, according as they have proceeded from the 

 opposite lateral halves of the Objective. These pencils are reflected 

 back to their own sides by the median Prism ; and each set, re- 

 ceived and reflected upwards by one of the lateral prisms, forms its 

 image in its own Eye-piece, the two images combining Stereo- 

 scopically, just as if the pencils which form them had been separated 

 at the lower end of the body. — This arrangement has the advan- 

 tage of being capable of use with high powers ; but as it involves 

 a decided loss of light and of definition, and as its construction is 

 both more costly and more liable to derangement than that of 

 Mr. Wenham, it is not likely to come into general acceptance. 



29. Nachefs Stereo-pseudoscopic Binocular. — An ingenious 

 modification of Mr. Wenham's arrangement has since been intro- 



Fig. 22. 



Arrangement of Prisms in Nachet's Stereo-pseudoscopic Binocular : 



1, for Stereoscopic ; 2, for Pseudoscopic effect. 



duced by MM. Nachet, which has the attribute altogether pecu- 

 liar to itself, of giving to the image either its true Stereoscopic 

 projection, or a Pseudoscopic ' conversion of relief,' at the will of 



* The Author cannot allow this opportunity to pass without express- 

 ing his sense of the liberality with which Mr. Wenham has freely pre- 

 sented to the Public this important invention, by which there can be no 

 doubt that he might have largely profited if he had chosen to retain the 

 exclusive right to it. 



D 2 



