36 ANSWERS TO PRACTICAL 



8. Can any two spectators see the same rainbow ? 



They cannot, because no two persons can be at the right 

 angle to get the same color from a drop. 



9. Why, when the drops of water are falling through the 

 air, does the bow appear stationary ? 



Because the drops succeed each other so rapidly that they 

 keep a constant impression on the retina. 



10. Why can a cat see in the night? 



Because the pupils of its eyes are larger, and so admit more 

 light. 



Why cannot an owl see in daylight ? 



The pupils of its eyes are large enough to admit of cleai 

 vision in the night, but they cannot be contracted, and so in 

 daylight the owl becomes dazzled with the excess of light 

 received. 



12. Why are we blinded when we pass quickly from a dark 

 into a brilliantly lighted room ? 



The pupils of our eyes admit too much light, but they soon 

 contract to the proper dimensions, and we can then see dis- 

 tinctly. When we pass out from a lighted room into the dark 

 street, the conditions are reversed. 



* 13. If the light on a distant planet is only^ that which we 

 receive, how does its distance from the sun compare with ours ? 

 As the light is inversely as the square of the distance, the 

 distance is 1/100= 10 times greater than ours. 



14. If when I sit 6 feet from a candle I receive a certain 

 amount of light, how much will I diminish it if I sit back 6 

 feet further ? 



As my distance from the light is doubled, the light is in- 

 versely as 2 2 , or only \ as bright. 



15. Why do drops of rain, in falling, appear like liquid 

 threads ? 



The impression the drop makes on the retina remains until 

 the drop reaches the ground. 



'*>. Why does a to~~'d turn darker when ivetf 



