OBJECTIVES AND EYEPIECES. 



In taking up this subject we would say at the 

 outset that it is fraughi with difficulties, as almost 

 all of the features are based on scientific facts 

 which can be explained by mathematical formulae, 

 but as it is our purpose to give intelligible explan- 

 ations 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 studv the subject 

 further, to consult such books as contain more 

 explicit information. 



As has already been said, the compound micro- 

 scope is composed of two lenses, the upper one of 

 which magnifies the image which is formed by the 

 lower one. We know that the purpose is to give a 

 greater magnification than can be obtained with 

 the simple microscope. The defects of chromatic 

 and spherical aberration will however become more 

 pronounced than they would in the simple form, 

 to such an extent as to nullify the benefit which 



j 



might be derived from the magnifying power only. 

 In fact, magnifying power in itself is of very little 

 value without the attributes obtained from the 



