cured at a small pecuniary outlay ; but these do not 

 give a distinct image nor do they make structure visible, 

 which, be it remembered, it is the purpose of the micro- 

 scope to do. 



The normal eye can distinguish about 200 lines to 

 the inch and in a microscope such magnifying power 

 should be used as will apparently separate the structure 

 which it is sought to see at least to this extent. To 

 illustrate, take a 1-6 inch objective of 0.85 N. A. and a 

 2 inch eyepiece. An objective of this kind, properly 

 corrected, resolves the test-object Pleurosigma angula- 

 tum, in which the 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 3-4 inch or 1-2 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 

 and the spaces between the lines have been separated 

 sufficiently to become visible to the eye. 



Beginners as a rule are apt to use too much magni- 

 fication, 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 decreased 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. 



100 



