46 ANSWERS TO PRACTICAL QUESTIONS 



35. Why can ^ve not see out of the windoiv after ive 

 have lighted the lamp in the evening ? 



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

 and they adapt themselves to the increased amount. 



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



It scatters the rays. 



37. Why can we not see through ground-glass 01* 

 painted windows ? 



They transmit the light irregularly to the eye, and not uni- 

 formly, like a transparent body. 



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



Because it is so distant that the eye can not detect the dif- 

 ference between the distance of the center and the circumfer- 

 ence. 



39. Why can ^ve see farther with a telescope than ivith 

 the naked eye ? 



Because it furnishes us more light with which to see a dis- 

 tant object. 



40. Why is not snow transparent, liJte ice ? 



Because it is discontinuous, and the rays of light are broken 

 by multitudinous reflections and refractions. 



4:1. Are there rays in the sunbeam which we can not 

 see? 



We can not see the heat or the chemical rays. 



42. Why, when we press the finger on one eyeball, do 

 we see objects double ? 



Because the rays from the same external object fall on parts 

 of the two retinas that do not correspond in position. 



43. Why does a distant light, in the night, seem like a 

 star ? 



Because its image on the retina is so small that deception 

 becomes easy. 



