4 THE USE OF THE MICROSCOPE. 
attached to the stand below the stage. Above the stage the 
stand supports a vertical tube, in which the body of the micro- 
scope slides up and down. 
The body is a tube, in the upper end of which is placed a 
combination of lenses, known as the eyepzece, while to the lower 
end is screwed another combination of lenses—the objective. 
Each microscope is provided with a couple of eyepieces and 
a couple of objectives of different magnifying power. An 
objective magnifying only a small number of times is called a 
low power ; one maguifying many times (200 diameters or more) 
a high power. Similarly eyepieces are spoken of as high or low 
according to their magnifying power. 
In order that an object may be seen clearly the objective 
must be at a certain definite distance from the object, the 
distance varying with different objectives, and to a slight extent 
with different observers. The higher the power employed the 
closer must the objective be brought to the object. As the 
position of the object on the stage of the microscope is a fixed 
one this distance is regulated by moving the body of the 
microscope up and down in the tube in which it slides. 
This process of focussing is effected in two ways: (1) by 
simply sliding the body up and down by hand: this is known 
as the coarse adjustment ; it should always be performed with a 
slight screwing motion, and can only be used when low powers 
are being employed. 
(2) With high powers the distance between the objective 
and the object examined is so small that a more delicate 
method of adjustment is necessary. This jine adjustment is 
effected by a screw with a milled head placed at the top of the 
vertical pillar forming the stand. By turning the head from 
left to right, in the direction of the hands of a watch, the body 
of the microscope is lowered and the objective brought nearer 
to the object: by turning in the reverse direction the objective 
is raised. 
In using the microscope attend to the following rules :— 
1. Always examine an object first with the low power. Hav- 
ing adjusted the eyepiece and objective, direct the light up the 
tube of the microscope by means of the mirror, and then place 
the object on the stage. Twist down the body until the objec- 
tive is about a quarter of an inch from the object ; look down 
the microscope, and gradually twist the body up until the 
