HOW DO I USE LIGHT? 



form of tiny balls, each of which is spinning very rapidly 

 in space. In this book we will agree with the theory that 

 light is a form of radiant energy and that it passes through 

 space by means of very rapid vibrations. Light travels at 

 the astonishing rate of over 186,000 miles a second. When 

 a candle is lighted, there are changes in the material of 

 which it is made, which produces light energy. This radi- 

 ates through space in all directions. Heat is also radiated 

 from hot bodies, and the disturbances in the aerial of a 

 broadcasting station send out electrical radiations. Evi- 

 dently, then, light, heat, and electricity may travel as 

 forms of radiant energy. It will be the purpose of this 

 unit to learn something about the ways in which light is 

 used in our everyday life. 



PROBLEM I. HOW DO I USE LIGHT? 



If you were ever up to see the sunrise, you know that as 

 daylight approaches, objects begin to change from hazy 

 gray outlines and become more and more distinct as light 

 falls on them, till, in the early sunlight, they appear in all 

 the colors of nature. We have just read that light is a 

 form of radiant energy. We know that light is frequently 

 associated with heat, and that plants in the garden get 

 heat energy as well as light energy from the sun. Recent 

 discoveries have shown that we, ourselves, are getting 

 good out of the light that a few years ago we had no idea 

 of. The ultra-violet ray in the sunlight aids us to keep 

 well and prevents certain diseases, while the hardness of 

 our bones and our freedom from certain diseases is due to 

 its effect. We know that light makes it possible to read, 

 to see things in their natural colors, as well as to take pic- 

 tures and make light signals. From times of earliest 

 civilization people used light for signaling. The Greeks 

 and Romans as well as our American Indians all had 

 elaborate light signals, just as we are warned today by our 



H. & W. SCI. I 10 



