FUNDAMENTAL CONSIDERATIONS 
9 
THE COMPOUND MICROSCOPE 
A. Its Construction: 
The principal parts of a compound microscope are: 
1. The base, generally horseshoe shaped, which rests on the table. 
2. The pillar, an upright bar, which is attached to the base below 
and supports the rest of the instrument. 
3. The stage, a horizontal shelf upon which is placed the prepara¬ 
tion or slide to be examined. The stage is perforated in the center 
for transmitting light reflected up by the mirror. On the stage are 
two clips for holding the glass slide. 
4. The mirror, situated below the stage, by which the light is 
reflected upward through the opening in the stage. 
5. The diaphragm, inserted in the opening of the stage or attached 
to its lower face, and used to regulate the amount of light reflected 
by the mirror. 
6. The body tube, a cylinder which holds the draw tube and lenses 
and moves up and down perpendicularly above the opening in the 
stage. The tube is raised or lowered either by sliding it back and 
forth with a twisting movement or by a rack and pinion mechanism. 
The latter is called the coarse adjustment. 
7. The jine adjustment, a micrometer screw back of the tube, 
which, on being turned, produces a very small motion of the entire 
framework which holds the body tube. 
8. The oculars or eyepieces which slip into the upper end of the 
draw tube . Each of these consist of two plano-convex lenses, the 
lower one being the larger and known as the jield lens because it 
increases the field of vision. The upper or smaller lens is called the 
eye lens. It magnifies the image formed by the objective. Midway 
between the field and eye lens is a perforated diaphragm, the object 
of which is to cut out edge rays from the image. 
According to the system adopted by the maker, oculars are desig¬ 
nated by numbers, as 1, 2, 3, 4, etc., or by figures which represent 
focal lengths. 
9. The objectives, which screw into the bottom of the body tube 
or nose piece. They consist of a system of two, three or four lenses, 
some of which are simple, others compounded of a convex crown 
lens and a concave flint lens. Objectives like oculars are usually 
