224 ELEMENTARY SCIENCE 



Except for it, there would be stronger contrasts between 

 sunlight and shadow. Such contrasts are characteristic 

 of dry, clear air, as in Arizona or New Mexico. 



Transmission of Light. If the light which encounters 

 a substance simply continues on its way without modifica- 

 tion we say that it is transmitted, and we call the substance 

 through which it is transmitted transparent or translucent, 

 depending upon the extent to which light passes through 

 it; if it does not transmit light, we call it opaque. Smooth 

 glass is transparent, while a sheet of white paper is trans- 

 lucent. A substance may both permit transmission and 

 cause reflection. This you have noted in passing show- 

 windows which are in the shade; they reflect your image 

 while at the same time permitting you to see through 

 them. 



So we may sum up by saying that the various things 

 that happen to light are transmission, reflection, absorption, 

 diffusion, and refraction. You will find that, in consequence 

 of these various light phenomena, various effects are pro- 

 duced which are of great importance to all of us. 



QUESTIONS 



1. Why are black clothes warmer than white? 



2. Why are greenhouses warmer than the air outside? 



3. What is the difference between light and heat? 



4. How can light be changed to heat? 



5. How do the waves of light, heat, and sound compare in length 



and speed ? 



6. What is a rainbow? 



7. Explain how color is produced. 



8. Why does a stick look bent when partly immersed in water? 



9. What is the difference between transparent and translucent 



objects? 



