CHAPTER DC 

 OPTICS OF THE MICROSCOPE 



440. Apparatus and material for Chapter IX. 



1. Microscope with oculars and ob- 4. Homogeneous immersion tester, 

 jectives. 5. Ocular micrometer; stage mi- 



2. Convex and concave lenses. crometer. 



3. Apertometer. 6. Homogeneous immersion con- 



denser. 



441. Optical facts of prime importance for the microscope. 

 In considering the optics of the microscope six fundamental facts 

 concerning light must be kept constantly in mind, for all of 

 them are involved to a greater or less degree in every microscopic 

 observation: 



(1) Light is composed of radiation which for visual purposes con- 

 sists of waves from Ao.4ju to Xo.y/x in length. 



(2) Light in a uniform medium extends in straight lines. 



(3) Light may be reflected. 



(4) Light is refracted in passing from one medium to another of 

 different density. 



(5) Light may be dispersed or grouped into colored rays from the 

 fact that rays of different wave length are differently bent (fig. 145, 2). 



(6) Light may be diffracted. 



Stated in briefest terms light exhibits the properties of: 

 (i) Wave motion; (2) Rectilinear motion; (3) Reflection; (4) 

 Refraction; (5) Dispersion; (6) Diffraction. 



442. Wave motion. From a body like the sun, the electric 

 arc and other sources of energy, radiations are given off in waves. 

 The radiation which is visible, forms but a very small segment of the 

 total radiation. In fig. 151 the visible radiation is shown between 

 wave lengths Xo.4/x and Ao.y/z, measured in air or in a vacuum. 

 Shorter waves are called ultra-violet, and longer waves infra-red. 



270 



