496 



APPENDIX. 



of a circle, by turning the milled head, c; thirdly, in the 

 addition of the apparatus for illumination placed beneath 



Fig. 269. 



the stage, all of which is fitted into the bar, b, and may be 

 moved up and down by a rack and pinion, which is obscured by 

 the part in which the dove-tailed slides move ; to this bar, b, 

 is fixed the tube, a a, into which the various condensers and 

 illuminators are adapted, and may be revolved by turning the 

 milled head, c ; by means of these two circular movements, the 

 efiect of oblique light may be shown upon all parts of an 

 object. The condenser of Mr. Gillett, before described in 



