THE MICROSCOPE. oT 
2, The fine adjustment, by which the exact distance 
between the objective and the object is obtained. 
The coarse adjustment is made either by a rack and 
pinion movement, or by the body sliding in a tubular 
portion of the stand. The first is the easier for a beginner, 
but the second becomes quite as easy with a little practice, 
care being taken when sliding the body to twist it round at 
the same time. With low powers the instrument can be 
easily focussed with the coarse adjustment alone, but with 
high powers the fine adjustment is necessary to get clear 
definition. This is always accomplished by means of a 
screw working against a spring. 
The stand is generally furnished with a hinge, by which 
the body can be placed either in a perpendicular or in an 
oblique position. With short bodied microscopes it 1s 
convenient to have the body perpendicular when the instru- 
ment is being used only occasionally, or for short periods, 
such as when examining tissues. But when long-continued 
observations are necessary it is very advantageous to have 
the body of the instrument inclined. 
PracticaL Hints. For most kinds of zoological re- 
search a large and expensive microscope is quite unnecessary ; 
but the objectives should be good, of small aperture, and not 
combinations of lenses which are separated for the lower 
powers. The stand should be strong and steady on the 
table, the adjustments should work smoothly, and when the 
fine adjustment is being used there should be no apparent 
movement of the object. 
The eye-pieces often get dusty. This may be ascer- 
tained by turning round the eye-piece in the body of the 
microscope, when any dirt on it will be seen to turn round 
also. This dust is best removed by means of a dry camel- 
hair brush. The objectives, especially the higher powers,. 
