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 Abbe 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 Abbe 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 hght 

 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. 



9. 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 



I . The mirror is a sub-stage attachment one surface of which 

 is plain and the other concave. The plain surface is used with 

 an Abbe condenser when the source of light is distant, while 

 the concave surface is used with instruments without an Abbe 

 condenser when the source of light is near at hand. 



