100 Wheatstone on the Binocular Microscope^ Sfc. 
its relief ; and the relative positions of every point, in depth 
as well as in length and breadth, can be correctly determined. 
The stereoscope affords a convincing proof that the two pro- 
jections of an object presented to the two eyes, suggest the real 
object far more effectively to the mind than a single projection to 
one eye does ; and those who have paid much attention to the ap- 
pearance of binocular pictures in the stereoscope, will not have 
failed to remark, that not only is double vision of importance 
to enable us more accurately to judge of the relief of bodies, 
but it also occasions us to perceive things which pass entirely 
unnoticed when monocular pictures alone are regarded. 
Fully impressed with these views, and convinced, from the 
reasons above stated, that a binocular microscope would possess 
great advantages over the present monocular instrument, I, 
shortly after the publication of my first memoir, called the 
attention both of Mr. Ross and Mr. Powell to this subject, 
and strongly recommended them to make an instrument to 
realize the anticipated effect ; their occupations, however, pre- 
vented either of these artists from taking the matter up. The 
year before last, previous to the publication of my second 
memoir, I again urged Mr. Ross, and subsequently Mr. Beck, 
to attempt its construction, and for a short time they interested 
themselves in the matter, but ultimately relinquished it for 
want of time, and in my opinion over-estimating the difficulties 
of the undertaking. 
It appears, however, from a communication in the ' Ame- 
rican Journal of Science ' of January, 1853, which has been 
reprinted in the last number of the ' Microscopical Journal,' that 
such an instrument has been actually constructed by Professor 
J. L. Riddell of New Orleans, and the results expected have 
been obtained. The method Mr. Riddell employs is similar 
to the one I recommended to Mr. Beck. After the rays from 
the object pass through the compound object-glass in the usual 
manner, he deflects them by means of a system of rectangular 
prisms into two directions parallel to the original, and suffi- 
ciently separated for the images to be seen by each eye. As 
in this arrangement there must be a considerable loss of light, 
I have proposed another which will not have this disadvantage, 
and which I will shortly submit to the Society. 
A binocular microscope is, however, by no means a novelty, 
and its invention dates nearly two centuries back. I have 
found, in the library of the Royal Society, a work entitled 
* La Vision parfaite, ou les Concours des deux Axes de la 
Vision, en un seul point de I'Objet, Par le P. Cherubin 
d'Orleans, Capucin.' This work was published at Paris in 
1677, and in it eight chapters and a plate are devoted to a 
