OBJECTIVES AND EYE-PIECES. 



Although considerable magnifying power may be 

 attained by the use of two single lenses arranged in 

 a compound form, there is no advantage in it, from 

 the fact that the faults in the lenses are correspond- 

 ingly magnified, and these are so considerable that 

 they destroy what it is the purpose of the microscope 

 to give a distinct image. 



Objectives, Classes. Objectives may be divided 

 into two classes, dry and immersion ; in the former no 

 intervening medium except air exists between the 

 cover and objective, while in the latter a fluid is used 

 to connect the upper surface of the cover to the front 

 surface of the objective. The use of immersion fluid 

 has several advantages, the first of which is that the 

 objective may be made to give better performance, as 

 will be explained later on ; the second is that more 

 light will be transmitted, as there is less loss of it by 

 refraction. 



It should be understood however that no advantage 

 will be gained by using immersion fluid with a dry 

 objective. It does not increase its effectiveness one 

 particle, on the contrary it detracts from its quality. 

 When it is stated that an immersion objective has a 



