IN NATURAL PHILOSOPHY. 35 



OPTICS. 



224. i . Why is a secondary bow fainter than the primary / 

 The primary is produced by one reflection and two refrac- 

 tions; the secondary, by two reflections and two refractions. 

 The additional reflection weakens the ray. 



Why are the colors reversed? 



We can understand this by looking at Fig. 159. In one 

 bow we see that the rays enter the drops at the top, and are 

 refracted at the bottom to the eye ; in the other, that the rays 

 enter at the bottom, and are refracted at the top to the eye. 



2. Why can we not see around a house or through a bent tube f 

 The rays of light move in straight lines. 



3. What color would a painter use if he wished to represent 

 an opening into a dark cellar f 



Black. 



4.. Is black a color? 

 No ; it is the absence of color. 

 Is white f 



Yes ; it is the presence of all color i. e., it is the compound 

 effect produced on the brain by seven different impressions. 



5. By holding an object rearer a light, will it increase or 

 diminish the size of the shadow ? 



It will increase it, because more rays are intercepted. 

 7. Where do w? see a rainbow in the morning? 

 In the west. 



the age of persons by their voices. An architect, comparing the length o* 

 two lines separated from each other, if he estimate within the 30th part, we 

 deem very accurate ; but a musician would not be considered very precise 

 who only estimated within a quarter of a note. (128-*-30 = 4, nearly.) In a 

 large orchestra, the leader will distinguish each note of each instrument. We 

 recognize an old-time friend by the sound of his voice, when the other senses 

 utterly fail to recall him. The musician carries in his ear the idea of the 

 musical key and every tune in the scale, though he is constantly hearing a 

 multitude of sounds. A tune once learned will be remembered when the 

 words of the song are forgotten. Prof. Pepper tells us that he tuned a fork 

 which corresponded to 64,000 vibrations per second. The first harmonic ia 

 produced by one-half the whole cord, the second by one-third, fec. 



