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114 APPLIED SCIENCE 



image. When the image is quite distinct, the surface is called a 

 mirror. When the surface is rough the rays are not reflected 

 regularly, but at different angles (Fig. 63). This action is 

 called diffused reflection. Diffused reflection throws the 

 rays of light in all directions and assists, therefore, in illumi- 

 nation. 



113. Refracted Light. Light travels faster in a rare 

 than in a dense substance. Therefore when a ray passes 



from a rarer to a denser sub- 

 stance, it is bent on entering and 

 on leaving the denser substance, 

 and in both cases the refraction 

 or bending is toward its base 

 (Fig. 64). When light passes 



from the air through water 

 FIG. 64. Refraction of Light. 



or a prism, the rays are bent. 



This fact is taken advantage of by manufacturers and 

 others who are located in thickly settled communities, 

 where the streets are narrow and the buildings are high. 

 The upper panes of the windows are then made of a 

 peculiar combination of prisms and lenses. By means of 

 this device, the rays of sunlight in the street or yard are 

 deflected from their original direction and projected and 

 diffused into the stores, rooms, and basements. All forms of 

 prismatic glass reflect the rays of light downward. 



114. Composition of Illuminanjs. All practical illu- 

 minants are made of carbon brought to incandescence 

 (glowing). The types of illuminants fall into two classes: 

 first, particles heated by the combustion of their own carbon, 

 such as candles, lamps, and gas flames; second, particles of 



