4O ANSWERS TO PRACTICAL QUESTIONS 



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



43. Why does a bright light, in the night, seem so much 

 nearer than it is ? 



44. Why does a ray of light, passed through a small hole, 

 of any shape, in a card, make a round, bright spot? 



45. Why are these spots crescent-shaped during an eclipse ? 



46. What color predominates in artificial lights ? 

 Yellow. 



47. Why does yellow seem white, and blue green, when seen 

 by artificial light ? 



Because the white takes on, in the yellow rays, a yellow 

 hue, and the yellow added to the blue gives a green, hence 

 there is no white for comparison. So, also, dark blue be- 

 comes purple, and red has a tawny hue. Magnesium light 

 possesses all the colors of the spectrum, and hence all objects 

 .retain their natural appearance when illuminated by it. 



48. Why are we not sensible of darkness when we wink ? 

 Because the impression of the light is retained upon the 



retina during the brief interval of darkness. 



HEAT. 



258. i. Why will one 's hand, on a frosty morning, freeze 

 to a metallic door-knob sooner than to one of porcelain ? 



Because the metal is a better conductor of heat than the 

 porcelain, and hence conducts the heat from the hand faster. 



2. Why does a piece of bread toasting ctirl up on the side 

 toward the fire ? 



The water being expelled from the pores on that side causes 

 the bread to shrink. 



3. Why do double windows protect from the cold? 



The non-conducting air enclosed between the window-panes 

 keeps in the heat and keeps out the cold. 



4. Why do furnace-men wear flannel shirts in summer to 

 keep cool, and in winter to keep warm f 



