CHAPTER XIV 

 OPTICS OF PROJECTION 

 790. Apparatus and Material for Chapter XIV : 



See the optical apparatus in Chapters I to XL 



791. History of the optics of projection and references to 

 literature. See the appendix and the works of reference in Ch. I, 

 2 ; works on general physics, optics and astronomy. 



792. For the most successful use of projection apparatus it 

 is necessary to understand some of the simplest principles of 

 optics, and to keep in mind that in the projection of images two of 

 the fundamental phenomena of optics are constantly present. 

 These two phenomena are: (i) Reflection and (2) Refraction. 



793. Reflection. By this is meant the change in direction of 

 rays of light when they meet a surface. The change in direction 

 of a beam of light striking a surface depends upon the character of 

 that surface. The principle kinds of reflection are, regular reflec- 

 tion, irregular reflection, and semi-regular reflection. 



794. Regular reflection. If the surface is smooth, as in a 

 mirror, the incident and reflected ray will be in the same plane and 

 will make equal angles on opposite sides of the normal erected at 



FIG. 309. REGULAR REFLECTION AT A POLISHED SURFACE. 

 The angle of incidence i, is equal to the angle of reflection r; and the incident 

 and reflected ray are in a plane perpendicular to the reflecting surface. 



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