1. Petroleum oil looks bluish green when it is on the water. Why?

2. Smoke and fine particles that float in the air deflect the short waves of light more than the long ones. Why? Why is the sky blue? Why is the sun red after a forest fire?

3. Should colors that are to be worn in an artificial light be selected by sunlight or by the artificial light?

4. Why does a piece of red cloth appear black when seen by blue light and red by red light?

5. Why is it desirable to have school windows reach to the ceiling?

6. Why is it desirable to have the light for writing come over your left shoulder?

7. Tell the advantages of rough gray plaster.

8. Why does a diamond sparkle?

9. Upon what principles may imitation stones be made?

10. When is a substance black?

11. Is black a color?

12. Is white a color?

13. Why are white clothes worn in the summer?

14. Why is a room with light walls better to work in than one with dark walls, even when the same amount of light comes in the room?

15. Why do rivers appear shallower than they really are?

16. Explain why a reddish lamp-shade makes a room more cheerful at night.

17. Colored lights are often seen in fireworks. What causes them?


1. An electric light bulb makes considerable noise when it breaks. Why?

2. How may a rotten spot in a wooden beam be detected?

3. Why is it that persons often hold the hand behind the ear that they may hear?

4. Watch a circular saw starting through a board and notice that the pitch of the buzzing tone is high. Why?

5. Why does the pitch fall soon after the saw enters the board?

6. Tap a steam pipe with a hammer. Can the sound be heard on the floor above?

7. If you burn gunpowder in the air it does not make a noise. If the gunpowder explodes in the cannon it makes a loud noise. Why?

8. Explain how a speaking tube acts so as to make sounds louder.

9. How do we know that sound does not travel through a vacuum?