82 ELEMENTARY CHEMICAL MICROSCOPY 



standard thread for the attachment of the objective OO'. Lying 

 in the axis of the tube C is the reflecting prism P, the surface 

 R of which is silvered, and the outer end L ground convex, thus 

 serving the purpose of a plano-convex collecting lens. An iris 

 diaphragm whose diameter is adjustable by the knob K is fas- 

 tened eccentrically to C. The position of the center of the dia- 

 phragm with respect to the axis of C may be changed by loosening 

 the screw S, thus making it possible to alter the position 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 eliminating 

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

 all adjustments of the light rays must be made by displacing the 

 iris diaphragm and thus changing the position of the spot of 

 light upon the reflecting surface R. 



The Leitz Vertical Illuminator 1 is so constructed as to permit 

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

 above the objective, and is therefore applicable to all heights and 

 powers of objectives. 



The construction is shown in Fig. 37. To a cylindrical adap- 

 ter K a collimator tube T is attached which carries a condensing 

 lens L in its mounting C. C slides within T, thus permitting 

 regulation of the diameter of the illuminating beam of light pro- 

 jected upon the reflecting surface. One side of K is flattened 

 and through this surface is cut an opening into the interior of the 

 cell. The lower part of this opening is dovetailed as shown at d. 



1 E. Leitz, Wetzlar, Germany. 



