IN POPULAR PHYSICS. 43 



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



light. 



11. Why can not an owl see distinctly in daylight ? 



Its eyes are adapted to faint light. That of bright sunshine 

 is therefore too dazzling. 



12. Why are we blinded tvhen 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 a dark 

 room, the conditions are reversed. 



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

 which ive receive, how does its distance from the sun com- 

 pare ivith ours ? 



As the intensity of light is inversely as the square of the 

 distance, the distance is ^,/100 = 10 times as great as ours. 



14. If ivhen I sit 6 feet from a candle I receive a cer- 

 tain amount of light, hoiv much ivill I diminish it if I sit 

 back 6 feet farther ? 



As my distance from the light is doubled, the brightness is 

 inversely as 2 2 , or only as great. 



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. 



16. W7iy does a towel turn darker when wet ? 



More of the light is transmitted, and less reflected. "We see 

 this illustrated in greasing a bit of paper. It becomes semi- 

 transparent because more light passes through it, but looks 

 darker itself because less light is reflected to the eye. 



17. Does color exist in the object or in the mind of the 

 observer ? 



