THE TYPES OF OCULAR LENS. 27 



drop of oil of cedar must be placed on top of the condenser, 

 and the slide, which must be as thin as possible, placed on it. 

 The cover-glass used should also be very thin. Either a 4 

 m.m. or an oil immersion objective may be used. For this 

 form of illumination an intense light is needed, either direct 

 sunlight or some form of improved electric lamp being best. 



QUESTIONS. 



What is refraction ? 



Give the two laws of refraction. 



What is the type of the microscope lenses ? 



What is the focus of a lens? 



What is meant by spherical aberration ? How is this corrected ? 



What are doublets and triplets? 



What is meant by refrangibility ? How is this corrected in microscope 

 lenses ? 



How many kinds of microscope are there? 



What is a simple microscope ? 



How is the magnifying power of lenses expressed? 



What is meant by a compound microscope? 



Give the different parts of a compound microscope ? 



What is meant by direct light? 



What purpose does a diaphragm serve? 



What is a condenser ? 



What is meant by an iris diaphragm ? 



What is a nose-piece ? 



How are the lenses of an ordinary microscope called ? 



What is an objective? 



How many lenses or combinations of lenses does an ordinary objective 

 contain ? 



How is the magnifying power of objectives designated ? 



What is meant by the focal distance of an objective? The working dis- 

 tance ? 



What is the difference between the dry and immersion objectives? 



What is a homogeneous immersion objective? 



What is meant by a non-achromatic objective? 



What is meant by an achromatic objective? An aplanatic objective ? 



What is an apochromatic objective? 



What is meant by an adjustable objective? 



What is the angular aperture of an objective? 



What is meant by the actual point of an objective? 



What is the optical axis of a microscope ? 



What relation does the size of the lenses have to its angular aperture? 



What is the numerical aperture of an objective ? What is the ocular of a 

 microscope ? 



Of how many lenses does it consist ? 



What is the difference between the positive and the negative ocular. 



What is a compensating ocular? A projecting? 



How are oculars designated ? 



What is the field of a microscope ? 



