94 



THE ART OF PROJECTING. 



TOTAL REFLECTION. 



This phenomenon is generally shown by properly 

 directing a beam of light into a vessel of water. 

 Perhaps the simplest way is to fill a glass beaker with 

 water, containing a little milk or a little magnesia 

 stirred into it for the purpose of enabling the eye to 

 trace the course of the light through it. Next placing 

 the beaker in a convenient place, with a bit of looking- 

 glass direct a small beam of light upwards through 

 the side of the vessel, so as to strike the under surface 

 of the water. By trial, the proper incident angle will 

 be found at which the light will not emerge from the 

 upper surface of the liquid, but will be totally reflected ; 

 the course of the beam will be easily traced through 

 the milky fluid. 



With suitable arrangements, very striking and beau- 

 tiful effects may be produced in a stream of water. 



Fig, 70. 



The high tanks made for showing the direction and 

 form of water jets are generally made with a glass 

 window opposite the orifice H, through which a beam 



