5 
viewed with it may be seen distinctly, the light must be concentrated by 
means of the condenser, and be conserved by means of a liquid, e. g. oil of 
cedar, having the same index of refraction as glass. The oil fills the space 
between the object and the objective. In this way the loss of light is prevented 
as shown in Fig. 4. 
6. The ocular or eyepiece, J, into which one looks when using the micro¬ 
scope, forms an image of the image formed by the objective; hence the term» 
compound microscope. Oculars of varying powers of magnification can be 
used, thereby enabling one to obtain any desired magnification, the practical 
working limit being 1200 to 1500 diameters. 
7. The mirror, K, is used to reflect the light into the condenser. One side is 
plane or flat for use with daylight, and the other side is concave for use with 
artificial light. In either case parallel rays are reflected into the condenser. 
(See Figs. 2 and 3.) 
8. Place the microscope in a vertical position on the desk with the coarse 
adjustment next you and near enough that you can look into the ocular easily. 
9. Lower the tube with the coarse adjustment until the front lens of the 
objective is within 6 m. m. of the stage. See that the iris diaphragm below 
the condenser is open. 
10. Remove the ocular. Swing the low power objective into position. 
While looking into the tube, adjust the mirror so that an image of the electric 
bulb is seen in the center of the lighted area, which is known as the field. 
Replace the ocular. The field should be uniformly bright. If it is not, alter 
the position of the mirror until it is uniformly lighted. 
(a) Turn the mirror slightly to the right. What is the effect? 
Turn the mirror slightly forward. What is the effect? 
( b ) Close the diaphragm. What is the effect? 
(c) Lower the condenser slowly while looking into the ocular. 
What is the effect? 
11. Whenever starting to use the microscope, examine it to determine that 
the iris diaphragm is open, the condenser is up as high as it will go and the 
concave side of the mirror is up. Place the instrument near the edge of the 
desk facing directly in. Adjust the light as described in paragraph 10. Do 
not move the microscope for the purpose of obtaining even illumination of the 
field. Use the mirror for this purpose. 
12. Examine a permanent, mounted preparation of the leg and wing of the * 
common house fly. 
13. In focusing the microscope upon any object to be viewed, the proper 
objective and ocular being in place, the tube is moved down by the coarse 
adjustment, L. until the objective is near the object, but not touching it. 
Looking into the ocular, the motion is reversed. When the image begins to 
show, the movement must become slow. 
14. With the lowest power a good focus can usually be obtained with the 
coarse adjustment. However, with the high powers the fine adjustment, M, 
must be used in order that the tube may be moved slowly. The fine adjust¬ 
ment works on a fine thread so that a complete revolution of the screw moves 
the tube very little. Care should be taken not to turn the screw completely 
down until it is “jammed” tight or so far upward that it is off the thread. 
