VERTICAL ILLUMINATORS, METALLURGICAL MICROSCOPES 83 



fastened eccentrically to C. The position of the center of the 

 diaphragm with respect to the axis of C may be changed by 

 loosening the screw S, thus making it possible to alter the posi- 



FIG. 34. Nachet Vertical Illuminator. 



tion of the point of incidence upon R of the illuminating rays 

 from the radiant, according to the power and mounting of the 

 objective employed. 



The light rays proceeding from the radiant pass through the 

 lens L, and striking the surface R, pass through the objective 

 which now acts as a condenser, throwing a tiny spot of intense 

 light upon the surface of a metal preparation M. The light rays 

 reflected from M reenter the objective to form the image seen 

 in the microscope. A noteworthy feature of this type of vertical 

 illuminator is the placing of the prism P in such a position as to 

 bring its lower surface as close to the upper lens combination of 

 the objective as it is possible to do. This greatly reduces the 

 danger of the formation of a hazy or cloudy image by elimi- 

 nating internal reflections. The position of the prism P is fixed, 

 hence all adjustments of the light rays must be made by dis- 

 placing the iris diaphragm and thus changing the position of 

 the spot of light upon the reflecting surface R. 



The Leitz Vertical Illuminator l is so constructed as to permit 

 the insertion of either a disk or a right-angled reflecting prism 

 above the objective, arid is therefore applicable to all heights 

 and powers of objectives. 



The construction is shown in Fig. 35. To a cylindrical adapter 

 K a collimator tube T is attached which carries a condensing 



1 E. Leitz, Wetzlar, Germany. 



