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 screv/ S, thus making it possible to alter the posi¬ 
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 ^ 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. 35. To a cylindrical adapter 
K a collimator tube T is attached which carries a condensing 
^ E. Leitz, Wetzlar, Germany. 
