PROJECTION OF IMAGE, ETC., UPON THE SCREEN. 65 
VI. PROJECTION OF IMAGE, AND FOCUSING 
UPON THE SCREEN. 
WE will suppose that the beginner has a dark 
room fitted up as described in the last section, and 
is ready to commence work. Having selected an 
object and placed it upon the stage of the micro- 
scope, he stands up before the instrument and 
looks over the preparation carefully, for the pur- 
pose of finding the best field to photograph. When 
he has decided upon this, and has adjusted his 
cover-correction — if the objective is provided 
with correction for cover —and his achromatic 
condenser, —if he is using one,— to secure the 
best possible definition and illumination, he re- 
moves the eye-piece. He then introduces a little 
cylinder of black paper or cardboard (dead black) 
into the tube of the microscope, to prevent reflec- 
tion from the inner surface of the tube. The 
screen is next placed at such a distance as seems 
best, and the image is roughly focused upon it 
from the microscope, by means of the coarse 
adjustment. It will be remembered that the ob- 
jective is always moved forward for this pur- 
pose, and that the greater the distance of the 
screen, the nearer the objective must come to 
the object. 
The operator now steps to the screen and care- 
fully focuses the image upon the ground-glass by 
means of the fine adjustment. The room must 
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