234 GENERAL SCIENCE 



green or yellow in daylight when it absorbs less of one of 

 these colors than it does of the other colors contained in 

 white light. So we see that color is really not a property 

 of bodies, but is the sensation that a body produces when 

 we view it in daylight. If viewed in light other than day- 

 light, objects will often produce different color sensations. 

 For example, a green ribbon will not appear green unless 

 viewed in light containing green rays. 



Sometimes a certain combination of colors will produce 

 white light even when part of the spectrum is lacking. 

 Two colors that will produce white light when mixed are 

 called complementary colors. Red and bluish green, 

 orange and light blue, light green and violet are such 

 combinations. . 



QUESTIONS 



1. Name six luminous bodies. 



2. Name six non-luminous bodies. 



3. Is the earth luminous or non-luminous? The moon? 

 What reasons have you for thinking so? 



4. How may we change a piece of iron from a non-luminous to 

 a luminous body? 



5. If the sun is 92,000,000 miles from 4;he earth, how long does 

 it take light to travel from the sun to the earth? 



6. The report of a gun is heard two seconds after the flash is 

 seen. How far away is the gun? 



7. A flash of lightning is seen five seconds before the thunder 

 is heard. How far away is the cloud? 



8. Name four transparent substances. Four translucent sub- 

 stances. Four opaque bodies. 



9. Gold is ordinarily opaque. May it be hammered thin 

 enough to be translucent? 



10. One book is held three feet and another book is held nine 

 feet away from the lamp. How many times as much light does the 

 first book receive as the second book? 



11. What are the positions of the sun, moon, and earth when we 

 have an eclipse of the sun ? An eclipse of the moon ? 



