INTRODUCTION TO PHYSIOLOGICAL OPTICS 403 



VIII 



INTRODUCTION TO PHYSIOLOGICAL 

 OPTICS 



ALL visible objects give out light, either of their 

 own making, like the sun, or that which comes 

 from some external source and falls upon their 

 surfaces. Rays that fall upon any surface may 

 disappear (absorption), or be thrown back from 

 the surface (reflection), or, if the body be trans- 

 parent, pass into it, in which case they are often 

 bent from their course (refraction). 



REFLECTION FROM PLANE MIRRORS 



Angles of Incidence and Reflection. Place in 

 front of the condenser in the lantern (Fi^. 63) 

 the diaphragm with 2 mm. aperture. Cover the 

 round window in the optical box with the plain 

 glass slide. Eemove the cork from the tin cylin- 

 der. Put a piece of lighted Japanese incense in 



