38 ANSWERS TO PRACTICAL QUESTIONS 



the second image will be brighter. Each image after that will 

 be weakened by the repeated reflection. 



27. Which can be heard at the greater distance, noise or 

 music f 



Other things being equal, music will penetrate much further 

 than noise. Boatmen call to each other, at a distance, in a 

 musical tone. A band is heard above the noise of the rabble. 

 It seems to be a wise arrangement of Providence that all harsh, 

 discordant noises should perish as soon as possible, and only 

 harmonious ones survive. 



28. Why are some bodies brilliant, and others dull? 



Some reflect the light better than others. A piece of stone 

 coal lying in the sun's rays will shine so brilliantly that one 

 will cease to see the coal at all, and will judge it to be a bright 

 metal. 



29. Why can a carpenter looking along the edge of a board 

 tell whether it is straight ? 



If the edge is straight, the light will be reflected uniformly 

 to his eye from the whole length. Any uneven places will 

 make dark and light spots. 



30. Why can we not see out of the window after we have 

 lighted the lamp in the evening f 



The glass reflects the light of the lamp back to our eyes, 

 and they adapt themselves to the increased amount. 



3 1 . Why does a ground-glass globe soften the light ? 

 It scatters the rays. 



32. Why can we not see through ground-glass or painted 

 windows ? 



They transmit the light irregularly to the eye, and not 

 uniformly, like a transparent body. 



33. Why does the moon's surface appear flat ? 



Because it is so distant that the eye cannot detect the dif- 

 ference between the distance of the centre and the circumfer 

 ence. 



