8 PRELIMINARY EXERCISES 



turn the milled wheel on top of the pillar to the right. 

 What happens to the objective ? Does it move quickly or 

 slowly ? The wheel on top of the pillar is called the fine 

 adjustment. Why ? 



D. TAKING OUT AND PUTTING IN THE EYEPIECE. Ele- 

 vate the tube so that the objective is an inch or more from 

 the stage. Grasp the tube with the left hand, and with the 

 other hand pull out the eyepiece by taking hold of the 

 milled ring at the top. Never put the ringers on the lenses, 

 but use an old, soft handkerchief for cleaning them. To 

 put the eyepiece in place, hold the tube as before, else the 

 objective may be forced against the stage and be broken. 



E. TAKING OFF AND PUTTING ON THE OBJECTIVE/ To 

 remove the objective, always elevate the tube. Grasp the 

 objective lightly at the milled ring on its lower end, with 

 the thumb and forefinger of the left hand, and with the 

 thumb and forefinger of the right hand unscrew the objec- 

 tive at the milled ring at its upper end. In this way the 

 objective will not be dropped and broken. To replace 

 the objective, reverse the operation. Practice this until 

 it can be done with ease and facility. 



F. LIGHTING THE OBJECT WITH THE MIRROR. Place the 

 wing of a house fly in a drop of water in the middle of the 

 glass slide. Carefully drop a thin cover glass on top of 

 the wing. Elevate the tube and place the object on the 

 stage. Then with the eye at the eyepiece and looking 

 through the tube, turn the mirror in different positions. 

 What happens ? What is the mirror for ? Examine the 

 mirror and note its surfaces. How do its two surfaces 

 differ ? What is the difference in effect when lighting the 



1 If microscopes with double nosepieces are used, this work is not- 

 necessary. 



