VERTICAL ILLUMINATORS, METALLURGICAL MICROSCOPES 93 



of the radiant into the opening of the vertical illuminator I. 

 By loosening the winged nut w a sufficient lateral movement 

 of the screen E may be obtained to properly align the optic 

 axis of c with the center of the opening of the vertical illumi- 

 nator I. 



The compound microscope. Fig. 41, is attached to the central 

 stand and consists essentially of a stage St supported by four 

 pillars attached to the plate 

 P, which in turn is movable 

 by worm gear F and microm- 

 eter screw/. 



The adaptation of a worm 

 gear for raising and lowering 

 the stage ensures that the 

 focus when once adjusted on 

 a specimen will remain sharp 

 even with heavy loads upon 

 the stage, without the use of 

 a special set screw to lock 

 the focusing mechanism. 



The microscope proper 

 consists of the tube T to 

 which are attached the 

 ocular tube N for photog- 

 raphy and the observing 

 tube M. 



The objectives screw into 

 metal ring-adapters which 

 drop into the objective open- 

 ing of the vertical illumi- 

 nator I; objectives can, therefore, be very rapidly changed. The 

 illuminator I has an opening at o through which the illuminat- 

 ing rays projected by c enter, and are reflected by a disk of 

 plain glass or a half-disk mirror attached to the milled head d. 

 The rays from the illuminated object lying polished side down 

 upon the stage pass downward through the disk of the illumi- 

 nator (or through the unobstructed half when the mirror is 



FIG. 41. Bausch & Lomb Optical Co. 

 Metallurgical Microscope. 



