MANIPULATION OF THE MICROSCOPE. 33 
standard. Such changes in adjustment are necessary only 
in the case of delicate work. 
5. Care of the Eyes.—Much of the difficulty some- 
times experienced by beginners with the microscope may 
be avoided by attention to three points mentioned above 
—the cleanliness of the lenses, a clear but not excessive 
illumination of the field, and a proper manipulation of 
the fine adjustment. In no case should the observer 
strain his eyes in the attempt to study what he cannot 
11.3437 
+3125 AS 4062 
7 4875 15 4687 
Brown & Sharpe Mfg. Co. 
Providence, RI. 
Fic. 22.—MIcROMETER CALIPERS. 
see clearly. If the object is not distinct, there must be 
something wrong which should be remedied. 
The distance of the eye above the eyepiece should 
vary with the magnification. For each combination of 
lenses there is a certain eye-point at which a maximum 
number of rays is most closely concentrated, and above 
or below,’ the size of the field will be reduced, and colored 
shadows will appear. The higher the power the nearer 
the eye-point approaches to the eyepiece. 
It is best to accustom oneself to the use of both eyes 
alternately, and to acquire the habit of keeping open the 
eye which is not over the instrument. At first the atten- 
