THE MICROSCOPE. 
the same time, and through the same object-piece by two or more 
different observers. 
Such is the principle upon which the multocular microscope 
of M. Nachet is based. 
90. A double instrument of this description is shown in fig. 43, 
where A is the object-piece directed vertically downwards on the 
stage ; above it is a case, containing a triangular prism which is 
so formed that the light reflected from its left side shall pass 
along the axis of the right-hand tube, and that reflected from 
its right side along the axis of the left-hand tube. Observers 
looking into eye-glasses set in these tubes, would therefore both 
see the same object in precisely the same manner. 
It may perhaps be objected, that the focus which would suit the 
eye of one observer, would not suit the other; the difference,, 
however, between the focal adjustments of different eyes is always 
so inconsiderable, that it can be equalised by a small motion 
given to the tubes carrying the eye-pieces. 
Microscopes, as they are usually mounted, reverse the objects, 
the top appearing at the bottom, the right at the left, and vice 
versa . This being found inconvenient in instruments used for 
dissection, where the motion of the hand and the scalpel of the 
operator would be reversed, expedients are provided by which the 
image is redressed, and the object viewed in its natural position. 
This is accomplished in the microscope represented in fig. 43, by 
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