84 
ELEMENTARY CHEMICAL MICROSCOPY 
lens L in its mounting C. C slides within T, thus permitting 
regulation of the diameter of the illuminating beam of light 
projected 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. The 
prism P and the disk k are attached 
respectively to the axis of the milled 
wheels W and W'. These in turn 
are mounted upon metal plates with 
edges obliquely cut so as to fit into 
the dovetail d. These plates when 
inserted and pressed in place are 
held by the spring .y. They are thus 
secured in proper position but can 
be slid back and forth in the slot d. 
A mark S upon the plates and an¬ 
other t upon the adapter serve to 
indicate the proper position of P or ^ with respect to the optic 
axis of the microscope M. To remove the prism, the wheel 
W is pressed gently downwards and outwards, thus releasing 
the plate from the spring 5; W is then carefully raised until 
the plate is free from the slot d. It can then be removed by 
tipping up slightly and withdrawing from the opening. To insert 
the disk, turn W' until the groove i is horizontal, introduce k into- 
the opening and push down till the lower edge fits into d, then 
press W' forward as far as it will go. The groove S is then brought 
into coincidence with t. The reflecting disk k is fastened to a 
mounting by the spring fingers v. This device permits the rapid 
and easy removal of the disk for cleaning or for replacement 
when broken. The objective 0 is screwed into the lower open¬ 
ing of K; O in the illustration is an 8 millimeter apochromatic, 
for 200 millimeters tube length, uncorrected for cover-glasses. 
Just as in the simple prism or disk illuminators, the rays of 
light striking the reflecting surface are directed downwards 
through the objective upon the object m. 
Fig. 35. Leitz Vertical 
Illuminator. 
