COMPOUND MICROSCOPES 17 
microscope is lighted again. Immediately above the analyzer 
and attached to the mounting of the analyzer a lens of a com- 
paratively long focal length has been placed in order to over- 
come the difference in focus created by the introduction of the 
analyzer into the optical rays. 
The condensing system is mounted on a slider, and, further- 
more, can be raised and lowered along the optical centre by 
means of a rack-and-pinion adjustment. If lowered sufficiently, 
the condensing system can be thrown to the side to be removed. 
from the optical rays. The condenser consists of three lenses. 
The two upper lenses are separately mounted to an arm, which 
permits them to be tilted to one side in order to be removed 
from the optical rays. The complete condenser is used only 
in connection with high-power objectives. As far as low-power 
objectives are concerned, the lower condensing lens alone is 
made use of, and the latter is found mounted to the polarizer 
sleeve. Below the polarizer and above the lower condensing 
lens an iris diaphragm is found. 
The microscope table is graduated on its periphery, and, 
furthermore, carries a vernier for more exact reading. 
The polarization microscope is not furnished with an ob- 
jective nose-piece. Every objective, however, is supplied with 
an individual centring head, which permits the objective to be 
attached to an objective clutch-changer, situated at the lower end 
of the microscope-tube. The centring head permits the objectives 
to be perfectly centred and to remain centred even if another 
objective is introduced into the objective clutch-changer. 
At an angle of 45 degrees to the polarization plane of polarizer 
and analyzer, a slot has been provided, which serves for the 
introduction of compensators. 
Between analyzer and ocular, another slot is found which 
permits the Amici-Bertrand lens to be introduced into the 
optical axis. The slider for the Bertrand lens is supplied with 
two centring screws whereby this lens can be perfectly and 
easily centred. The Bertrand lens serves the purpose of 
observing the back focal plane of the microscope objective. In 
order to allow the Bertrand lens to be focused, the tube can be 
raised and lowered for this purpose. An iris diaphragm is 
mounted above the Bertrand lens. 
