THE MICROSCOPE. 



at pleasure the object-piece from over the stage, to change or clean 

 the lenses. The arm, 9, can be fixed in its position by the pin, 

 whose milled head is 10. 



The instrument is focussed first by moving the body to and from 

 the stage by means of t^e pinion, 7, and rack, 5, the adjustment 

 being completed by a much slower motion imparted to the body 

 by the milled head, 11, which is connected with a screw and lever, 

 by one revolution of which the body is moved through the 

 300th part of an inch. An elastic play is allowed to the body, so 

 as to guard against injury by the accidental contact of the object- 

 piece with the slide. 



The usual rectangular motions are imparted to the stage, 12, 

 through the extent of an inch, by the milled heads, 13, which 

 act on pinions, by which the racks are driven which carry the 

 stage right and left, and backward and forward. The illumi- 

 nating mirror, 14, is supported in the usual way, so as to be placed 

 at any desired angle with the axis of the instrument. Below the 

 stage is fixed an arm, 15, capable of being moved up and down 

 by rack and pinion. This arm supports a tube, 16, intended to 

 receive apparatus to modify the light transmitted by 14 to the 

 object. Various apparatus for condensing and otherwise modify- 

 ing the illumination are provided, which fit into this tube, 16. 

 A motion of revolution round its axis is given to this tube by the 

 milled head, 17. By these means, the effect of oblique light can 

 be shown on all parts of the object. A condenser, 18, invented 

 by Mr. Gillet, of a peculiar construction, provided with a series 

 of diaphragms formed in a conical ring, is inserted beneath the 

 stage. 



Polarising apparatus, and other appendages, can also be attached 

 to the secondary stage. 



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