GENERAL DIRECTIONS xi 



lenses for focusing light upon the stage. On the lower side of the condenser is an 

 iris diaphragm, made up of movable leaves; the size of the opening between the 

 leaves can be changed by means of a button located at the side of the diaphragm. 

 Turn the microscope upside down so that you can see the diaphragm and observe 

 the effect of sliding the button back and forth. The mirror has two surfaces, 

 plane and concave. When the condenser is in use, the plane surface of the mirror 

 is to be employed, as the concave mirror converges the light, and thus conflicts 

 with the action of the condenser. 



2. The lenses. Find on a shelf in the microscope box, two cylindrical metal 

 cases. Unscrew these and remove from them the objectives. These objectives 

 are marked 3 and 7 (German system) or 16 mm. and 4 mm. (American system). 

 Note that 3, or 16 mm., is shorter, has a larger lens, and is therefore of a lower 

 power of magnification than 7, or 4 mm. Screw the objectives into place in the 

 nosepiece, holding each with both hands while doing so to avoid possibility of 

 dropping. 



On another shelf in the miscroscope box will be found two eyepieces or oculars. 

 These are Nos i and 3, or 4X and 8X ; the first-named one is in each case the 

 lower power. Place the No. i or 4X eyepiece in the top of the tube. 



3. The adjustment screws. On the arm between the pillar and the tube is a 

 pair of vertical screws. These move the tube considerable distances at each 

 turn, and are therefore designated as the coarse adjustment. At the top of the 

 pillar is a horizontal screw, the fine adjustment, which moves the tube only a 

 very short distance at each turn. Turn each of the screws and note the effect 

 on the tube. When the fine adjustment is turned clockwise, the tube moves 

 down; when counter-clockwise, it moves up. 



4. To use the low power: 



a) Swing the low-power objective into place, and place the low-power eye- 

 piece in the top of the tube. 



b) While looking through the eyepiece, turn the mirror toward the light 

 until the field of the microscope becomes suddenly bright. 



c) Place the object to be examined, mounted on a glass slide, in the center 

 of the opening on the stage. . , 



d) Lower the tube by means of the coarse adjustment until the objective is 

 close to the slide. 



e) While looking into the eyepiece, slowly raise the tube by means of the 

 coarse adjustment until the object comes into view. The object is now said to 

 be in focus. Note the distance from the object at which the lower power comes 

 to focus. 



/) Adjust the light to the best advantage by means of the iris diaphragm. 

 This is a very important point. Students, as a rule, use too much light, which 

 drowns out the details of the object and is hard upon the eyes. Always adjust 

 the light for every object looked at. 



