0 EN ee eS eee lle 
COMPOUND MICROSCOPES 9 
3. The stage is either stationary or movable, round or 
square, and is attached to the limb just above the hinge. The 
upper surface is made of a composition which is not easily 
attacked by moisture and reagents. The centre of the stage is 
perforated by a circular opening. 
4. The sub-stage is attached below the stage and is for the 
purpose of holding the iris diaphragm and Abbé condenser. 
The raising and lowering of the sub-stage are accomplished by 
a rack and pinion. 
5. The iris diaphragm, which is held in the sub-stage below 
the Abbé condenser, consists of a series of metal plates, so ar- 
ranged that the light entering the microscope may be cut off 
completely or its amount regulated by moving a control pin. 
6. The fine adjustment is located either at the side or at 
the top of the limb. It consists of a fine rack and pinion, and 
is used in focusing an object when the low-power objective is in 
position, or in finding and focusing the object when the high- 
power objective is in position. 
7. The coarse adjustment is a rack and pinion used in raising 
and lowering the body-tube and in finding the approximate 
focus when either the high- or low-power objective is in position. 
8. The body-tube is the path traveled by the rays of light 
entering the objectives and leaving by the eye-piece. To the 
lower part of the tube is attached the nose-piece, and resting 
in its upper part is the draw-tube, which holds the eye-piece. 
On the outer surface of the draw-tube there is a scale which 
indicates the distance it is drawn from the body-tube. 
g. The nose-piece may be simple, double, or triple, and it 
is protected from dust by a circular piece of metal. Double and 
triple nose-pieces may be revolved, and like the simple nose- 
piece they hold the objectives in position. 
THE OPTICAL PARTS 
1. The mirror is a sub-stage attachment one surface of which 
is plain and the other concave. The plain surface is used with 
an Abbé condenser when the source of light is distant, while 
the concave surface is used with instruments without an Abbé 
condenser when the source of light is near at hand. 
