OBJECTIVES AND EYEPIECES. 



In taking up this subject we would say at the outset 

 that it is fraught with difficulties, as almost all of the 

 features are based on scientific facts which can be best 

 explained by mathematical formulae, but as it is our 

 purpose to give intelligible explanations to those who 

 may not be conversant with algebraic expressions, 

 many of the statements and descriptions will appear 

 rather dogmatic. We can but advise those who wish 

 to study the subject further, to consult such books as 

 contain more explicit information. 



For the purpose of simplicity the compound micro- 

 scope has up to this time been spoken of as being 

 composed of two lenses, the lower of which magnifies 

 the object and the upper magnifies the image formed 

 by the lower lens. While this expresses the principle, 

 as a matter of fact the microscope is never so con- 

 structed as the defects of chromatic and spherical aber- 

 rations would be more pronounced than in the simple 

 microscope, even to such an extent as to nullify the 

 benefit which might be derived from the increased 

 magnifying power alone. In fact, magnifying* power in 

 itself is of very little value without the attributes 



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