110 



lines average 60,000 to the inch. With the above 

 eyepiece it is utterly impossible to see them, while 

 if it is replaced by a J inch or ^ inch eyepiece, they 

 can easily be distinguished. This is not owing to 

 any peculiar quality of the eyepiece, but merely to 

 the fact that by increasing the magnifying power, 

 the dimensions of the object have been increased 

 to such an extent that the lines have apparently 

 been separated and become visible to the eye. 



Beginners as a rule are apt to use too much 

 magnification or amplification, and often attempt 

 to view a large surface with an objective which 

 will show but a small part of it. It must not be 

 forgotten that the apparent field of view is de- 

 creased as higher powers are used and that a 

 low power will give a better impression of a large, 

 coarse object and its relative parts, because it 

 makes a larger surface visible. 



/;/ objectives of the same power, but of different 

 angular apertures, the magnifying power and field 

 will always be tJie same. 



The following table will probably be of assist- 

 ance to the beginner. After he has become better 

 acquainted with his instrument his judgment will 

 dictate to him what to do. 



A power of 25 diameters will show a surface of 

 about "4- inch diameter. 



u_ U 



A power of 50 diameters will show a surface of 

 about T V inch diameter. 



