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. JSTachet 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 i& 

 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 

 86 



