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 S/ 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- 
Fig. 41. Bausch & Lomb Optical Co. 
Metallurgical Microscope. 
nator I; objectives can, therefore, be very rapidly changed. The 
illuminator I has an opening at 0 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 
