APPENDIX. 497 



page 206, is represented byj^ as being fitted into the tube, a. 

 For the purpose of illumination by artificial light, Mr. Gillett 

 has contrived the apparatus represented in fig. 269 : the 

 mirror is, in this case, removed, and upon the stem, a, which 

 supports it, is fitted the bent bar, h c, having attached to it 

 another thin bar, for the support of a disc of enamel, e. In 

 the foot, f, is fixed the rod, ff g, upon which are two slides, 

 one a thin piece of mahogany, h, into which a small camphine 

 lamp, I, fits ; and the other, i, to which is attached a para- 

 bolic reflector, h, for condensing the light upon the disc, e, 

 the reflector having a hole at m, through which the rays 

 from the disc pass to the object. By this apparatus a light 

 is obtained similar to that produced by the reflection of the 

 sun from a white cloud. 



The method of adjusting and using the apparatus fitted into 

 the tube a, plate xi., is thus described by Mr. Ross : — 



The secondary stage, situated underneath the general stage, 

 which holds the objects, is for supporting all the various forms 

 of illumination, also polarizing apparatus and other auxiHaries, 

 which are employed underneath the object. This consists of 

 a cylindrical tube, a a, moveable in rectangular directions, and 

 affixed to a dove-tailed sliding bar, 5, which can be removed 

 for the convenience of easily applying the various apparatus ; 

 this bar fits into a second sliding bar, moveable by a rack and 

 pinion, parallel to the axis of the microscope. The rectangular 

 motions given to the cylindrical tube serve to adjust the appa- 

 ratus, which may be applied centrally or excentricaUy, while 

 the sliding bars regulate the distance of the apparatus from 

 the stage, and consequently from the compound body. 



When about to use the Gillett's illuminator in day-light, 

 the secondary stage and the slide to which it is attached are to 

 be withdrawn from the instrument, and the illuminating appa- 

 ratus applied in the cylindrical tube of the secondary stage ; 

 the slide is then to be replaced and pressed upwards against a 

 stop, then finally regulated by means of the rack and pinion 

 which moves the second slide, the upper surface of the illumi- 

 nating lens is to be adjusted so as to be level with the upper 

 surface of the object-stage. Having the compound body 

 vertical or conveniently inclined for use, turn the arm and 

 32 



