142 Miscellaneous Intelligence. 
pieces. The author’s aim in its construction was solely the riot 
ment of the impression by presenting an image to each eye, for he a 
sumes, according to the then prevalent error, that vision by the two or- 
gans conjoiotly is naturally aud necessarily unique, from the perfect 
conformity of all the homonymous parts of the two images of the ob- 
ject on the two retine. ‘The real advantage of such an instrument en- 
tirely escaped his attention; viz., that of presenting to the two eyes 
the two dissimilar microscopic images of an object, under precisely the 
same circumstances as the two unlike images of any usual object is 
presented to them when no instrument is employed, by which simulta- 
neous presentm oe the same accurate judgmentas to its real solid form 
and the relative distances of all its points, can be as readily determine 
ed in the former case as in the latter 
n the gaeras of a binocular microscope there is one thing es- 
pecially to be attended to—viz., that the images be both direct, for in 
The reason of these effects is fully explained in Sections 5, 10, 22, 23, 
of my Memoirs. The reversal of the images by re flection from mir- 
rors or reflecting prisms, will produce the same result as to the a 
oscopic and pseudoscopic appearances as their inversion by lens 
The binocular microscope constructed by the Pére d’ rléans was 
pseudoscopic, though be describes one which, had it been made, woul 
have been stereoscopic ; he was, however, quite unaware that there 
would be any difference of this kind between them. The pseudoscopic 
effects when inverted images are presented, and the natural appear- 
ances when erecting eye-pieces are employed, have not escaped the 
observation of Mr. Riddell, 
Besides actual inspection by means of the binocular microscope, 
there i . another way in which the advantages of binocular vision may 
nal, ma 
they were not accompanied by their ‘Stereoscopic complements. 
very simple modification of the usual microscope would fit it for pro- 
ed round on an iniagin is within itself, from But this 
method is inapplicable = the light be perfectly diffused and uniform 
o as to avoid all shadows, the presence of which would give rise to 
false stereoscopic a euarenunh In the former case, ahem the object 
remains stationary and the tube moves independently of the frame, the 
a of the light so as to sca re gle shadows might a an ad- 
van and judgme 
assist the visual j 
; 
t 
