92 



THE AMEHICAN MONTHLY 



[April, 



microscope is altered only by a triangular groove along the whole 

 length of the lateral margin, and by an enlargement of the cen- 

 tral aperture. Into this a heavy diaphragm may be slipped with 

 an opening of the usual size for the Abbe condenser. 



The apparatus for mechanical movement is essentially the ordi- 

 nary mechanical stage, but working directly by hand instead of 

 by rack and pinion, the especial advantage being the free long 

 movement thus permitted. It is in two parts. A rectangular 

 frame (a) showing front margin, and (^) as seen from behind, the 

 lateral bar of which is beveled to fit into the triangular groove in 

 the side of the stage plate, in which it slides forward and back- 

 ward ; and a thin plate {6 and /) longer than the preceding and a 

 little narrower, its beveled edges sliding laterally in a V-^h'iped 

 groove on the inner edges of the anterior anfl posterior bar of the 



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frame just mentioned. The projecting ends of this plate serve as 

 hand-rests in dissecting. Three small screws are set in it as stops 

 for the slide, and the knobs by which it is moved are bored in the 

 centre as sockets for the stage forceps. Its central opening is of 

 the same size as the larger opening in the stage-plate, and in this 

 rests loosely a circular piece of glass (c) with a central opening 

 {d), on which a dish may be set in examining small alcoholics. 

 This apparatus, when well fitted and smoothly ground, works 

 with a nicety and precision scarcely, if at all, inferior to that of 

 the geared movement. An ordinary slide in position is shown at e. 

 This stage was made October, 1890, to my order and from my 

 drawings, by the Mcintosh Optical Company of Chicago, from 

 whom I learn that it is now furnished with many of their own 

 instruments, being adapted to the round stage-plate of their micro- 

 scopes by placing under it a thin false stage-plate which bears 

 beneath a socket that slips into the central opening of the stage. 



